Dissertations / Theses on the topic 'Antarctic benthos'

Introduction- First chapter introduces the Antarctic coastal marine environments, as part of the intriguing and challenging “puzzle” that scientific community is committed to resolve, represented by Antarctica and its changes. A brief glimpse on two of the main drivers influencing benthic communities dwelling in these areas, the sea-ice and the substrate, is given, with a special eye on the unresolved aspects of their influence on marine organisms and on the effect of their variations. Some of the major challenges of scientific researches in such extreme and fragile environment is highlighted together with an overview on ongoing and proposed strategies of the Scientific Committee on Antarctic Research (SCAR). Especially focusing on monitoring perspective, the essential requirement of the establishment of permanent sites and of specially protected areas is discussed. Later on, an overview on the study site and its inhabiting key species is presented. Recent advances in underwater technologies confer the opportunity to overcome previous technical limitations and to improve our capacity of investigation in similar areas. Between emerging techniques, non-destructive image-based ones are introduced in their theoretical aspects. Another pivotal aspect of monitoring is the strategy of sampling, one of the major issues on which relies the reliability of a monitoring project. Preliminary considerations on the relevance of choice of the best sampling design are described. Materials and Methods- Second chapter describes the methodologies used to collect, elaborate and analyse data obtained from images. Firstly, field operations are described, corresponding to well-established protocol of nondestructive image-based SCUBA-operated sampling on shallow rocky bottoms. A particular attention is provided to the use made of sampled materials during the in-silico procedures. This is a newness element of this project, providing one of the first examples of application of some emerging image-based techniques in Antarctica. The informative potential that archived and new SCUBA-operated videos are able to store up about epifaunal communities composition and structure has been exploited by applying photogrammetric reconstruction and measurements. Due to the dated format of older videos, a procedure of adaptation to new applications was needed. In order to better explain these steps, a brief and simply panoramic on some major features of, as defined, ‘historical’ videos is given. Thanks to the proposed in-silico procedures, it has been possible to describe three-dimensional features of seafloor and dwelling organisms, also from videos not specifically meant for this purpose. Later in the chapter, it is shown how spatial information about specimens distribution has been obtained thanks to a variety of GIS tools. Finally, it is supplied a summary of the statistical analyses used to the multiple aims of: i) exploring data, ii) describing macrobenthic populations and their spatial distribution, iii) deriving best sampling design for key species, iv) producing comparisons across years (thanks to two temporal repetitions) and sites. Results- Third chapter reports the main results deriving from the different ‘fields of study’ of the research, including: i) a first section, specifically focusing on the photogrammetric output, with a special eye on the issues related to the use of ‘historical’ materials, as the used video samples were defined; and ii) a second, more ecological, section, reporting the results from counting procedures and spatial statistical analyses. The taxonomical composition of the megabenthic community is described: extendedly, in form of list of taxa that was possible to distinguish and eventually recognize at the lower taxonomical level as possible; and synthetically, by the estimation of biodiversity indices. The small-scale spatial pattern analysis is, then, reported, highlighting the distribution and neighbour estimates of different taxa. Sampling strategy has different outcomes if applied to organisms with different distributions and, thus, when it is advisable to preventively study these spatial aspects. In our case, statistical analyses on sampling simulation suggest specific combinations of sample size and sampling scheme for the main keyspecies analysed. Finally, the results of the trial linear regression model between the distribution of the sea urchin Sterechinus neumayeri (Meissner, 1900) and of the encrusting algae Corallinales are reported, confirming the need of a major number of covariates in order to understand distributional pattern shaping factors. Discussion- The final outcomes of the study are reviewed, according to the original aims and with the major issues of the research. The interpretation of some of the results is particularly investigated. The future perspectives are also mentioned, in many of the possible fields of improvement. Conclusions- Due to the overall value of the proposed methodological approach and of the results of the study, they are presented as contibution to the definition of a standardized protocol of monitoring techniques for the Antarctic benthos, in the perspective of a shared international collaboration.

The aim of this study was to investigate spatial changes in the trophic and energy pathways of the benthic community in the shallow shelf waters of the sub-Antarctic Prince Edward Islands (PEI). A combination of stable isotope and fatty acid analyses were used to provide a time-integrated view of the assimilated feeding history of selected components of the PEI benthic community. This study forms part of the larger project entitled “Variability in the Southern Ocean ecosystems” and is a contribution to the South African National Antarctic Programme (SANAP). During austral autumn 2009, benthic specimens were collected from 10 stations (from depths of 70 to 295 m) in different regions around the PEI: inter-island shelf (upstream, between and downstream of the islands) and nearshore. Historical data were combined with new data collected during 2009 to assess the long-term trends in the feeding ecology of the benthos in the region of the islands. The stable isotope and fatty acid signatures of the benthic suspension- and deposit-feeding organisms generated during this study suggested that these two communities incorporated both phytoplankton and kelp in their diets. Stable isotope, and to a lesser extent fatty acid signatures, indicated that kelp contributed more to the diets of those organisms in close proximity to the kelp beds (nearshore stations) than those from the inter-island region. Overall, however, pelagic phytoplankton was the dominant food source in the diets of all organisms, even for those living near the kelp beds. Notable exceptions were the sponges and bryozoans, in which kelp and phytoplankton contributed similar proportions to their diets, most likely resulting from a size restricted feeding mode. There were, therefore, no distinct spatial differences in the importance of the various food sources. However, fatty acid compositional data indicated increased food quality between and within the lee of the islands compared to upstream. The organisms collected upstream of the PEI had substantially lower quantities of total fatty acids (TFAs) than organisms of the same species collected from nearshore, open shelf or downstream stations. The increased food quality between and within the lee of the islands was likely a result of the “island mass effect”, which reflects increased phytoplankton concentrations at the PEI. The fatty acid profiles of hyperbenthic shrimp Nauticaris marionis, a key species in the PEI ecosystem, revealed no distinct ontogenetic or spatial patterns. This result is in contrast to the stable isotope analyses, which detected both spatial and ontogenetic differences in the diet of the shrimp. Nearshore shrimp were more ₁₃C-enriched than those from the inter-island region, suggesting increased kelp entering the food web within these regions. In addition, the shrimps demonstrated enrichment in δ₁₃C and δ₁₅N signatures with an increase in size, resulting in a relatively distinct separation of size classes, thus reflecting niche separation through their diets. The fatty acid profiles revealed that the shrimp all contained large proportions of polyunsaturated fatty acids (PUFAs) and essential fatty acids (EFAs), indicating that the quality of food consumed was similar among size class and region despite the niche separation and variation in carbon sources utilised. In addition, diatom and dinoflagellate fatty acids (20:5ω3 and 22:6ω3, respectively) occurred in the highest proportions in N. marionis, highlighting the importance of phytoplankton (indirectly) in their diet. These results represent strong evidence that phytoplankton is an importance food source in the PEI ecosystem. The temporal investigation of isotope signatures in the benthos at the PEI indicated that N. marionis demonstrated an overall depletion in δ₁₃C signatures over the period of 1984 to 2009 (nearshore: -2.55 ‰, inter-island: -2.32 ‰). Overall, the benthic community showed similar depletions in δ13C signatures (from -1.96 to -4.70 ‰), suggesting that shifts have occurred in the carbon signatures at the base of the food web. The depletion in δ₁₃C signatures of the benthos at the PEI most likely reflects increased contributions of smaller slow growing phytoplankton cells (more depleted signatures than large fast growing cells) in the diets of these organisms over time. These diet shifts, in turn, suggest a decrease in productivity has occurred at the islands, likely due to a decreased frequency and intensity of the “island mass effect”. Decreased phytoplankton productivity at the PEI likely results from the southward shift in the average position of the sub-Antarctic Front (SAF), most likely in response to climate change, which in turn promotes flow-through conditions rather than retention at the PEI.

This Thesis covers two different topics in Antarctic marine benthic invertebrates. The two main goals are: 1) to improve the knowledge of the biodiversity of the shallow water benthic communities inside Deception Island (South Shetland Islands, Antarctica), and 2) to establish the chemical ecology of selected Antarctic organisms, by studying the antifouling and antimicrobial activity of their organic extracts. Deception Island is an active volcano on the southwestern end of the South Shetland Island chain. This island chain parallels the northeastern curvature of the Antarctic Peninsula, but is separated from the Antarctic continent by the narrow Bransfield Strait. Volcanic activity is believed to be the key environmental component that controls epibenthic and infaunal invertebrate populations in Port Foster. Compared to nearby islands, Deception Island is clearly defaunate at depth, and since the last eruption in 1970, has been considerably recolonized. However, many taxa are still very poorly represented and the colonizer species are mainly those with planktotrophic larvae. Interestingly, the soft-bottom benthos communities of the shallowest zone of Port Foster has been barely and poorly explored yet. A complete study of the benthic invertebrate shallow community at Deception Island was conducted, looking for a comprehensive view of this singular spot working at different trophic levels. Shallow-water sediment at Deception Island is inhabited mostly by opportunistic, motile species, living under the influence of serious and long-lasting disturbances, related more to high sedimentation rates within the bay and the absent of hard substrata, than with the ice-scouring or anchor-ice disturbances (mostly absent inside the caldera, but common elsewhere in Antarctica). The trophic relationship between the water and benthic community has been described in four stages; (i) particulate matter is suspended from the seafloor into the water column; (ii) nutrients stimulate bacterial and phytoplankton production, which stimulates zooplankton production; (iii) large suspended particles provide food for planktonic and benthic grazers; and (iv) organisms no consumed sink to the seafloor to be utilized by benthic community. These nutrients would be transmitted to bacterial communities, known to use this abundant material over the year in some sites of the island. This microbial biomass could then be transmitted to the meiofauna, trophic level showing also high densities in Port Foster. Furthermore, Port Foster receives much runoff during the austral summer, and may serve as a “nutrient trap”, thus influencing the meiofaunal organisms. All these, together with the microbial communities, could be behind the high macrofaunal densities observed here. Finally, all these trophic compartments would then be supporting the remarkable density of megafaunal organisms at Port Foster. Antarctic benthos is dominated by biological interactions, and it is expected that many marine invertebrates use chemicals as means of defense from predators, pathogens or preventing overgrowth. Natural products (also called secondary metabolites) are chemicals produced by organisms, which regulate the biology, co-existence, and co-evolution of the species without participating directly in their primary metabolism. The role of these natural products play in the Antarctic benthic communities is one of the main subjects of investigation in the present dissertation through an experimental contribution in the antimicrobial and antifouling field using chemical crude extracts from Antarctic benthic organisms. Marine secondary metabolites may play a role as deterrents against pathogenic microorganisms, fouling organisms, predators and/or competitors. Benthic marine organisms, under intense pressure for space, light and food, have developed a wide range of defensive mechanisms ranging from behavioral to physical and chemical strategies. Competition for space is a remarkable ecological force, comparable to predation that produce a strong selective pressure on benthic invertebrates. Some invertebrates, thus, possess antimicrobial compounds to reduce surface bacterial growth. The ubiquity of fouling organisms in the marine environment and the negative consequences of fouling are likely strong evolutionary pressures for marine organisms to develop defenses to protect their surface from fouling. In summary, marine invertebrates can survive in the highly competitive and hostile environments, mainly relying on their chemical defensive system by accumulating a series of defensive chemicals in their bodies or releasing the compounds to their surroundings.
Isla Decepción es un volcán activo en el extremo suroeste de la cadena de islas Shetland del Sur. Esta cadena de islas discurre paralela a la curvatura noreste de la Península Antártica, pero está separada del continente antártico por el estrecho de Bransfield. Se cree que la actividad volcánica es el componente ambiental clave que controla las poblaciones de invertebrados epibentónicos e infaunales en Puerto Foster. En comparación con las islas cercanas, Isla Decepción está claramente depauperada en profundidad, y desde la última erupción en 1970, sus fondos han sido recolonizados progresivamente. Sin embargo, muchos taxones están poco representados y las especies colonizadoras son principalmente aquellas que tienen larvas planctotróficas. Curiosamente, las comunidades bentónicas de fondos blandos de la zona más somera de Puerto Foster apenas han sido estudiadas. En un contexto en que la Península Antártica está experimentando una de las tasas más rápidas de cambio climático regional en la Tierra, Isla Decepción se presenta como una buena oportunidad de trabajar con escenarios previsibles para las comunidades bentónicas antárticas costeras. Se ha realizado un estudio completo de la comunidad bentónica de invertebrados en aguas poco profundas de Isla Decepción, en busca de una visión integrada de este paraje singular estudiando diferentes niveles tróficos. El bentos antártico está dominado por interacciones biológicas, y es previsible que muchos invertebrados marinos utilicen productos químicos como medio de defensa contra los depredadores, contra patógenos o para evitar el recubrimiento (antifouling). El papel que estos productos naturales desempeñan en las comunidades bentónicas antárticas es uno de los principales temas de investigación en la presente tesis a través de una contribución experimental en el campo de los antimicrobianos y del antifouling utilizando extractos crudos de organismos bentónicos antárticos. Los invertebrados marinos pueden sobrevivir en entornos altamente competitivos y hostiles, confiando principalmente en su sistema defensivo químico mediante la acumulación de una serie de sustancias químicas defensivas en sus cuerpos o liberando los compuestos a su entorno.

The current thesis covers two important and poorly known aspects of Antarctic bryozoans: biodiversity and chemical ecology. The comparative analyses of diversity carried out here (Chapters 1 and 2) between Antarctica and the last separated fragments of Gondwana support the hypothesis of the sequential separation of Gondwana. We discuss that the high number of species from the Argentine Patagonian (AP) region shared with Antarctica found in our study question the real extent of Antarctic isolation for cheilostome bryozoans. The presence of shared common bryozoan species between these two regions may also be explained by the free migration of marine organisms in and out of the Polar Front, via the deep abyssal plains and the potential passive northwards transport of larvae (or perhaps even adults) to considerable distances, via the branch of the Antarctic Circumpolar Current (ACC) flowing northward along the continental shelf of Argentina, the Falkland/Malvinas Current. The role of the Scotia Arc and other dispersal pathways, like eddies of ACC, and human dispersal mechanisms, may increase the bryozoan connection found between the Antarctica and the AP region. Also, our studies (Chapters 1 and 2) are among the first characterizations of the bryozoan communities, mainly at the slope, from the AP region, and from the Southern Ocean (SO), specially the Weddell Sea. The bathymetric distribution from the AP region and the SO found in our studies fits well with the limits of the continental shelf, the slope and the deep sea. Interestingly, our research also shows an expansion in the known distribution of diverse bryozoan species from the AP region and the SO. Our results stress the importance of taxonomical studies in these scarcely explored regions, reporting a high number of new genera and species, and new records too. Among the new species found in our study, a bryozoan of the genus of Reteporella characterized by rare giant spherical avicularia is described in Chapter 3, leading us to discuss which are the potential roles of the avicularia. Since the studied bryozoan communities, below areas affected by local disturbances (iceberg scours and anchor ice), are mainly subject to biotic factors such as competence and predation, the evolution has favoured the development of chemical mechanisms in benthic organisms, which have also been investigated here (Chapters 4 and 5). Our studies are among the first reports on chemical ecology of Antarctic bryozoans. In order to study these chemical interactions, new adapted protocols were designed using sympatric and abundant predators. Our findings demonstrate the importance of diverse chemical ecology mechanisms against competence and predation in Antarctic bryozoans. Most bryozoan species tested here display cytotoxicity and/or repellent activity against the sea urchin Sterechinus neumayeri and the amphipod Cheirimedon femoratus, respectively (Chapter 4). In Chapter 5, our results demonstrate that bryozoans seem to be readily defended against at least one of the two abundant predators, Odontaster validus and C. femoratus. The intra- and interspecific variability in bioactivity suggest an adaptive response to diverse abiotic and biotic factors, presence of microorganisms and/or genetic variability. The general trend in our study indicates the presence of a combination of both chemical and physical defensive mechanisms in most bryozoan species, suggesting complementary traits. In general, these results lead to the conclusion that this phylum is very active with extended repellent activities.
Aquesta tesi cobreix dos aspectes importants i poc coneguts dels briozous antàrtics: la biodiversitat i l'ecologia química. L'anàlisi comparatiu de diversitat realitzat aquí (Capítol 1 i 2) entre l'Antàrtida i altres zones geogràficament properes recolzen la hipòtesi de la separació seqüencial de Gondwana. Es discuteix que l'elevat nombre d'espècies de la regió de la Patagònia argentina (PA) compartides amb l'Antàrtida qüestiona el grau real d'aïllament de l'Antàrtida en briozous queilostòmats. Els nostres estudis (Capítols 1 i 2) són també una de les primeres caracteritzacions de les comunitats de briozous, principalment del talús, de la regió de la PA, i de l' Oceà Austral, especialment el Mar de Weddell. Els nostres resultats remarquen la importància dels estudis taxonòmics en aquestes regions escassament explorades, incloent un gran nombre de nous gèneres i espècies, i noves cites. Entre les noves espècies trobades en el nostre estudi, es descriu un briozou del gènere Reteporella caracteritzat per una rara aviculària esfèrica i gegant, portant-nos a reconsiderar quines són les possibles funcions de l'aviculària (Capítol 3). Com les comunitats estudiades de briozous, per sota de les zones afectades per pertorbacions locals (erosió per icebergs), estan subjectes principalment a factors biòtics com la competència i la depredació, l'evolució ha afavorit el desenvolupament de mecanismes químics de protecció (Capítols 4 i 5). Els nostres estudis són dels primers en ecologia química de briozous antàrtics. Els nostres resultats demostren la importància de diversos mecanismes d'ecologia química contra la competència i la depredació en briozous antàrtics. La majoria de les espècies de briozous mostraven activitat citotòxica i/o repel•lent contra l'eriçó de mar Sterechinus neumayeri i l'amfípode Cheirimedon femoratus, respectivament (Capítol 4). En el capítol 5, totes les espècies de briozous estudiats mostraven activitat de repel•lència alimentària contra almenys un dels dos depredadors abundants considerats, l'estrella de mar Odontaster validus i l'amfípode Cheirimedon femoratus. La tendència general en el nostre estudi indica la possessió d'una combinació de mecanismes físics i químics en la majoria de les espècies, fet que suggereix estratègies complementàries.

Climate changes effects include ocean acidification and, possibly, the alteration of frequency and magnitude of climate events, such as El Niño. All environmental global changes are supposed to be a major threat to ecosystem, both terrestrial and marine. Despite the amazing bulk of literature on these last, few efforts have been devoted to polar regions, which are actually likely to be the most fragile environments on the Earth. In this work we want to elucidate the response, to environmental modifications, of three Antarctic benthic macroinvertebrates: the scallop Adamussium colbecki, the sea urchin Sterechinus neumayeri and the sea star Odontaster validus, inhabiting the littoral area of Terra Nova Bay (Ross Sea, Victoria Land). Using long term series, we investigated potential correlation between A. colbecki recruitment and environmental variables (sea ice cover duration and El Niño events), reporting that A. colbecki recruitment is not affected by these variables. We also performed a manipulative experiment in the Mario Zucchelli Station to understand the effects of three pH levels (8.16, 7.8 and 7.6) on the three species, investigating the response of hard tissues and of the reproductive system. Results show that S. neumayeri spines are affected by low pH only at nanoscale and only in hardness property, while the shell of A. colbecki is not altered at all. As far as reproductive system, we found a significant effect in the gonado-somatic index and on stage development of A. colbecki, in addition to some damages in the gonad tissue, although not statistically significant. S. neumayeri shows the same disrupt tissue all over ovary and testes, although differences from the control are not statistically significant. Conversely, O. validus does not show any effect of low pH exposure at all. Further investigations are necessary to understand the energy costs of maintenance of the polar organisms and its potential consequence on individual life history and, thus, populations dynamic.

Knowledge of the abundance, distribution patterns, and population ecology of antarctic benthic biodiversity have increased considerably during the last decades. Antarctic marine benthic biodiversity has been sampled primarily in areas close to research stations and mainly at shallow depths since more than 100 years using a range of sampling methods, including benthic sleds or trawls and grabs each of which targets a particular community or habitat. Recent technological advances and increased availability of remotely operated vehicles (ROVs), manned submersibles, and video equipped towed gears have significantly increased accessibility to mid and outer continental shelves, continental slopes, submarine canyons and seamounts, thus allowing the direct observation and quantitative study of megabenthic assemblages wthout any impact on the benthic community. Due to the high cost and logistics of these benthic sampling, particularly in Antarctica, studies are often limited to only one biological sampling method. Results of biodiversity studies are used for a range of purposes, including taxonomy, trophic ecology, growth rates, reproductive ecology, environmental impact assessments, and predictive modelling, all of which underpin appropriate marine resource management. However, the generality of marine biodiversity patterns identified among different sampling methods is unknown. This is one of the resons why more comparative studies are necessary to better understand the ecosystem patterns and processes in antactic regions in a context of climate change scenario. Major regions of the Antarctic shelf appear to be undergoing rapid climate change, such as warming on the Antarctic Peninsula in the past few decades. Such climate change will affect benthic ecosystems through changes in benthic-pelagic coupling. For these porpouse this tesis pretend to generally understand the distribution and the eocological paper that benthic organisms have on the benthic ecosystem of the antarctic continental shelf. This thesis includes for chapters In the first chapter we investigate ophiuroid assemblages in terms of the distribution and diversity patterns at three different environmental regimes and depths in the Antarctic Peninsula. In the second chapter we assessed the health status of Antarctic gorgonian assemblages in a pristine and remote area in the southernmost part of the Weddell Sea continental shelf. In the third chapter we compared the performance of two sampling gears by assessing quantitative data on the continental shelf of three oceanographically very distinct regions in Antarctic Peninsula. Finally in the fourth chapter we tried to understand the way in which a gorgonian population affects the diversity of the surrounding megafaunal species, by characterizing gorgonian assemblages dwelling on two very contrasting continental shelves.
El conocimiento de la abundancia, los patrones de distribución y la ecología de población de la biodiversidad bentónica antártica ha aumentado considerablemente durante las últimas décadas. La biodiversidad bentónica marina antártica se ha muestreado principalmente en áreas cercanas a las estaciones de investigación y principalmente a poca profundidad desde hace más de 100 años utilizando una variedad de métodos de muestreo, incluidos trineos o redes de arrastre bentónicos, cada uno de los cuales se dirige a una comunidad o hábitat en particular. Los recientes avances tecnológicos y una mayor disponibilidad de vehículos operados a distancia (ROV), sumergibles tripulados y aparatos de muestreo equipados con videocámara han aumentado significativamente la accesibilidad a las plataformas continentales, taludes continentales, cañones submarinos y montañas submarinas, lo que permite la observación directa y el estudio cuantitativo de comunidades megabentónicas sin ningún impacto en la comunidad misma. Debido al alto coste y la compleja logística de estos muestreos, particularmente en la Antártida, los estudios que se generan a menudo se limitan a un solo método de muestreo biológico. Los resultados de los estudios de biodiversidad se utilizan para una variedad de propósitos, que incluyen taxonomía, ecología trófica, tasas de crecimiento, ecología reproductiva, evaluaciones de impacto ambiental y modelos predictivos, todos los cuales sustentan la gestión adecuada de los recursos marinos. Sin embargo, se desconoce la generalidad de los patrones de biodiversidad marina que se pueden identificar entre los diferentes métodos de muestreo. Esta es una de las razones por las que se necesitan más estudios comparativos para comprender mejor los patrones y procesos de los ecosistemas en las regiones antárticas en un contexto de escenario de cambio climático. Las principales regiones de la plataforma antártica parecen estar experimentando un cambio climático rápido, como el calentamiento en la Península Antártica en las últimas décadas. Dicho cambio climático afectará a los ecosistemas bentónicos a través de cambios en el acoplamiento bento-pelágico. Para estos motivos esta tesis tiene como objetivo general comprender la distribución y el papel ecológico que tienen los organismos bentónicos sobre el ecosistema bentónico de la plataforma continental antártica. Esta tesis incluye cuatro capítulos En el primer capítulo se investigan las asociaciones de ofiuras en términos de patrones de distribución y diversidad en tres regímenes ambientales y profundidades diferentes en la Península Antártica. En el segundo capítulo se evalúa el estado de salud de las poplaciones de gorgonias antárticas en un área prístina y remota en la parte más meridional de la plataforma continental del mar de Weddell. En el tercer capítulo se compara el rendimiento de dos artes de muestreo mediante la evaluación de datos cuantitativos en la plataforma continental de tres regiones oceanográficamente muy distintas en la Península Antártica. Finalmente, en el cuarto capítulo se trata de entender la forma en que una población de gorgonias afecta la diversidad de las especies de megafauna asociadas, caracterizando conjuntamente dos poblaciones de gorgonias que habitan en dos plataformas continentales muy diferentes.

The temperature record from the Antarctic Peninsula (AP) shows a warming trend 3°C greater than that of the Antarctic continent (Vaughan, et al., 2003). The LARsen Ice Shelf System, Antarctica (LARISSA) project was developed as an interdisciplinary collaboration to understand the impacts of global climate change on the ice shelf systems of the Peninsula. The 2010 LARISSA cruise to the western AP margin collected the two marine sediment cores from the mouth of Barilari Bay used for this thesis, Jumbo Piston Core (JPC) 127 and Jumbo Kasten Core (JKC) 55. The 77 sediment samples collected at 10 cm intervals were sieved at 63 microns to retain foraminiferal tests, identified to the species level. The 35 most abundant foraminifera species were grouped into five assemblages with one outlier species through Hierarchical Cluster Analysis (HCA), predominantly grouped by calcareous and agglutinated foraminifera. The Principal Component Analysis (PCA) yielded two principal components, which accounted for 81.5% of the variability within the data, correlated to the species Fursenkoina spp. and Bulimina aculeata. The base of this core was found to be nearly 8000 calibrated years before present (cal. yr. BP) through radiocarbon dating of the foraminiferal tests. The PCA results were correlated with the magnetic susceptibility down core, producing a timeline of four distinct zones in the mid- to late Holocene at the outer Barilari Bay core site. The earliest zone indicated stable cold bay waters, followed by a drastic change with the incursion of warmer Circumpolar Deep Water (CDW) onto the continental shelf. The third zone of this study illustrated a period of fluctuation between the cold bay waters and the CDW, interrupted by the Little Ice Age when the ice shelf in Barilari Bay extended to the mouth of the bay. The most recent zone depicts the past 200 years of melting ice shelves and the resulting increase in primary productivity observed in the bays of the western AP, discernable from the diatom, foraminifera, and sedimentological record. This description of the benthic foraminiferal record in outer Barilari Bay increases the understanding of the timing of events in the mid- to late Holocene and will serve as a correlation to other paleoclimate proxies from the LARISSA project.

Il numero sempre più alto di studi condotti sui microbiomi ha evidenziato l’importanza che queste associazioni rivestono nello sviluppo, nella salute e nella fitness degli organismi con cui i microbiomi vivono associati. In ambienti estremi come l’Antartide, i microbiomi sembrano avere un’importanza cruciale nel creare interazioni fondamentali per l’adattamento dei loro ospiti. Gli obiettivi di questa tesi sono: i) studiare la biodiversità dei microbiomi associati a diversi invertebrati marini antartici, ii) esplorarne l’origine, confrontando i microbiomi associati agli organismi con le comunità batteriche che abitano nei sedimenti circostanti, e iii) verificare se i fattori ambientali svolgano un ruolo attivo nel modellare la loro composizione tassonomica. I risultati hanno mostrato che, nonostante i microbiomi associati ai policheti antartici (Leitoscoloplos geminus, Aphelocaeta palmeri, Aglaophamus trissophyllus) possano variare in modo significativo tra gli individui, è possibile individuare dei core, sia a livello intraspecifico sia interspecifico, che contribuiscono significativamente all'intera comunità batterica associata. I taxa batterici associati ai policheti sono completamente diversi da quelli presenti nei sedimenti circostanti, suggerendo una potenziale trasmissione verticale o diverse capacità adattative dei microbiomi ai due diversi “habitat”. Molteplici fattori (i.e., non solo fattori ambientali ma anche quelli biologici come lo stato fisiologico e le abitudini di alimentazione) influenzano, a diversi gradi, la composizione tassonomica dei microbiomi associati ai policheti antartici. Nella stella marina antartica Odontaster validus la posizione geografica è il principale fattore che spiega le differenze trovate nella composizione tassonomica dei microbiomi, sebbene siano state riscontrate alcune somiglianze tra individui raccolti in luoghi diversi, suggerendo la presenza di altri fattori in grado di selezionare comunità batteriche simili. La presenza esclusiva di batteri specifici associati a stelle marine che vivono in determinate aree suggerisce una potenziale trasmissione orizzontale dei microbiomi, probabilmente acquisiti attraverso diverse abitudini alimentari che le stelle marine hanno sviluppato nelle suddette aree. Questa tesi di dottorato fornisce nuove informazioni sui microbiomi antartici, evidenziando una forte variabilità della loro composizione e complessità delle relazioni con gli ospiti esaminati, potenzialmente dovute, oltre ai fattori ambientali, anche alle caratteristiche biologiche degli ospiti.
Growing studies on host-associated microbiomes are highlighting the important role of microbes in the development, health and fitness of their hosts. This might be particularly true in remote and extreme environments, such as the Antarctic ecosystem, where the host and its microbiome could evolve together establishing peculiar and close interactions. This study aims: i) to investigate the biodiversity of microbiomes of different Antarctic invertebrates, ii) to explore the potential sources of the host-associated microorganisms by comparing them with microbial communities inhabiting the surrounding sediments, and iii) to verify the role of environmental setting in shaping their taxonomic composition. Results revealed that microbiomes of Antarctic polychaetes (Leitoscoloplos geminus, Aphelocaeta palmeri, Aglaophamus trissophyllus) showing significant variability among individuals, but that both intra-specific and inter-specific core microbiomes contribute for a significant fraction to the whole microbial assemblage. Bacteria associated with polychaetes were completely different from those in the surrounding sediments, suggesting a potential vertical transmission or the presence of different adaptative/selective conditions of the two “habitats”. Multiple factors (i.e., not only environmental factors but also biological ones such as physiological state and feeding habits) can influence to different extent the taxonomic composition of microbiomes associated with Antarctic polychaetes. In the Antarctic sea star Odontaster validus, the geographic location was identified as the main factor influencing the taxonomic composition of microbiomes, but this was not a general rule. In fact, high similarities were found among microbiomes of individuals collected in different locations, suggesting the presence of other drivers able to select similar microbial communities. The presence of exclusive bacterial families in sea-star microbiomes suggests a potential horizontal transmission of bacterial taxa, probably acquired through different feeding habits that the sea star might have developed in the different basins. This PhD thesis provided new information on Antarctic microbiomes, highlighting a strong variability of their composition and complexity of the relationships with the investigated hosts, potentially due to, besides environmental settings, also to hosts’ biological features.

Microbial mats are important components of perennially ice-covered Antarctic lakes in the McMurdo Dry Valleys, where they often comprise the dominant biomass in this cold, shaded environment. These lakes represent some of the most extreme lacustrine environments on Earth, including a persistent ice-cover, stable, stratified water columns, with strong salinity related density gradients. In these low-disturbance environments, the microbial consortia develop macroscopic emergent structures such as pinnacles and ridges. Such structures are speculated to confer advantageous survival traits and have also been found in the Precambrian fossil record as “conophyton” stromatolites – arguably some of the earliest evidence of life – and it has been suggested that a better understanding of the growth dynamics of modern “conophyton” will inform our understanding of what was required for these early fossils to be produced. Despite decades of research, there are few studies of the structural basis of conophyton producing microbial mats in Antarctic lakes. To help address this gap, complex microbial mats along a transect established in Lake Fryxell, one of the McMurdo Dry Valley lakes, were examined; with the aim of documenting the distribution of different types of photosynthetic organisms and mat morphologies along environmental gradients such as light, conductivity, oxygen concentration and depth. Microbial mat samples were taken along the transect and analysed in New Zealand using confocal laser scanning microscopy, along with conventional pigment extraction techniques. Correlations between mat morphology, pigment content and lake properties were found. The appearance of bacteriochlorophylls, characteristic of green sulfur bacteria within and below the oxycline confirm a shift from aerobic to anaerobic metabolism that was consistent with mats taking on a prostrate appearance. The cyanobacterial pigment phycoerythrin was only found in the hyperoxic, relatively well lit region of the transect, and was associated with the mats forming a distinctive macroscale morphology with dense fields of cm-scale cuspate pinnacles. Between these, a hypoxic region was characterised by a relatively flat mat within which were many cm-scale pits. Structural investigations were focussed on two distinct morphologies, pinnacle and honeycomb mat. Nearly all photosynthetic organisms were located in the upper 2 mm of both pinnacle and honeycomb mats, mainly comprising diatoms and cyanobacteria. Pinnacle mats were dominated by a narrow cyanobacterium, probably a species of Leptolyngbya, which were mostly oriented vertically, which placed trichomes parallel to the direction of pinnacle extension. The honeycomb mat contained fewer narrow trichomes, rather the bulk of photosynthetic organisms were diatoms from the genera Muellaria, Navicula and Diadesmis, together with broad-trichome cyanobacteria that formed a thin skin on the surface of the mat, though absent from the pits. The type of emergent structure that is formed appears to be related to species composition, and this in turn appears to be related to the growth conditions. A model was developed to explain how species-specific growth mechanisms are involved in emergent structure formation for honeycomb and pinnacle mats.

The Southern Ocean has unique seasonal qualities due to the Antarctic Circumpolar Current (ACC) thermo-isolating the Antarctic continent. During summer months, surface primary productivity from algal blooms is very high. In the winter months, limited daylight hours (4 in winter) and formation of sea ice prevents sun light from reaching surface waters, therefore limiting productivity. The short seasons of productivity and long winters in Antarctica combined with seasonal changes in deep ocean temperatures, salinity, and fluxes of organic matter impact foraminiferal population dynamics. Fluctuations in surface primary productivity, as well as living foraminiferal assemblages have been documented around the Antarctica Peninsula, but the impact on benthic foraminiferal assemblages is poorly understood. This is a study of seasonal affects on benthic foraminiferal assemblages in the southern Bransfield-northern Gerlache Straits of the Southern Ocean. Surface sediment samples from 600 meters and 1200 meters water depth were collected during two seasonal cruises: early April to record the productivity of the end-of-summer bloom and late June to sample the less-productive winter period. Three hundred and sixty samples were collected from 7 sites and processed using standard techniques. To identify living foraminifera, samples were treated with Rose Bengal, and CellTracker Green on a select set of samples for comparison. Ninety total species were identified; seventy species from June and seventy-one from April, fifteen species of foraminifera unique to April, thirteen to June and two unique species in the CellTracker Green samples. The abundance of total living (stained tests) opportunistic benthic foraminiferal species from the 7 sampled sites show distinct temporal differences related to seasonality. An assemblage of deep water species was also found, as well as an assemblage of shallow water species. ANOVA and post hoc Tukey tests showed that the full cores must be analyzed to determine seasonal species assemblage changes. Cluster analysis and species abundances in CellTracker Green samples showed a marked difference from the Rose Bengal samples, consistent with literature that suggests the two methods differ. Fluctuating populations of foraminifera in fossil samples can be interpreted as changes in local or global climate. This study stands as a modern analog for fossil foraminiferal assemblages, and provides important information to help interpret paleoenvironmental conditions related to seasonality by defining seasonally and geographically distinct species assemblages.

La Antártida es una masa de tierra y hielo rodeada por un mar con una plataforma continental profunda, caracterizado por temperaturas bajas y bastante constantes. La estacionalidad de luz y la capa de hielo son los responsables del aumento de la producción primaria de fitoplancton en primavera-verano y del flujo vertical de materia orgánica particulada (MOP), compuesto por fitoplancton fresco, excrementos del zooplancton y detritus. Los suspensivoros, así como otros organismos sésiles y vágiles, adaptaron sus estrategias de alimentación a estos pulsos de MOP. Estos organismos componen una comunidad bentónica muy diversa, aun siendo su fuente de alimento similar. Las condiciones ambientales más constantes y la alta productividad en las temporadas de primavera y verano provocan diferentes morfologías, tipos de alimentación, almacenamiento de energía y estrategias reproductivas, expresadas en una gran diversidad presente en la comunidad macrobentónica. La relación de estos organismos bentónicos y la dinámica de los alimentos son muy complejos y en gran parte desconocidos, teniendo múltiples variantes. Junto a los ecosistemas de aguas profundas, los ecosistemas bentónicos polares de la Antártida y del Ártico son difíciles de muestrear y observar. Sin embargo, el estudio del acoplamiento bento-pelágico es necesario para entender cómo los ecosistemas de la Antártida van a tolerar la transformación en curso debido principalmente al rápido cambio climático detectado en algunas zonas. Es de vital importancia entender las relaciones tróficas, cuales son las fuentes de materia orgánica que contribuyen a la dieta y cómo los organismos bentónicos adquieren e invierten la energía en función de su nivel trófico. El principal objetivo de este trabajo ha sido estudiar las variaciones de la respuesta espacio-temporal del bentos, ocasionada debido a los cambios de la disponibilidad de la materia orgánica, examinando las características ambientales y sus efectos sobre las comunidades bentónicas en el mar de Weddell (lado este del Mar de Weddell - Austassen-Kapp Norvegia y Península Antártica - estrecho de Bransfield y Larsen A, B y C). Una combinación de marcadores tróficos (isótopos estables, ácidos grasos, y el balance bioquímico (proteína-carbohidrato-lípido)) se utilizó a tal fin. Estos marcadores integran señales tróficas, lo que permite una comparación espacial y temporal de la acumulación de materia orgánica y de almacenamiento de energía en suspensivoros bentónicos. La ecología trófica de dieciséis representativas especies de invertebrados bentónicos fue estudiada y produjo una mejor interpretación del acoplamiento bento-pelágico en este desconocido ambiente. Las siete especies de gorgonias (Primnoisis sp., Fannyella nodosa, Ainigmaptilon antarcticum, Notisis sp., Primnoella sp., Dasystenella sp. y Thouarella sp.) recolectadas en el otoño de 2000 en Austasen, mostraron casi los mismos valores de isótopos estables del fitodetritus presente en las llamadas “green carpets" (acumulaciones de fitoplancton provenientes de la parte superficial de la columna de agua) y del microzooplancton. La dieta está por tanto basada en material sedimentado y re-suspendido, apoyando en parte la hipótesis de que algunos suspensivoros afrontan con éxito el invierno antártico, gracias a esta fuente de alimentos de larga duración. El balance bioquímico indicó un almacenamiento de energía diferente dependiendo de la especie y, posiblemente, de su estrategia reproductora. Para entender el papel de la estacionalidad en las comunidades bentónicas, se estudió la ecología trófica del alcionario Anthomastus bathyproctus a finales del otoño de 2000 y finales del verano de 2011 en la Península Antártica. La presa principal (el tunicado Salpa thompsoni) también se estudió en ambas épocas del año para entender su papel en el balance de energía y la contribución a la dieta del suspensivoro pasivo. Las principales presas del alcionario eran diferentes cuando se compararon ambas temporadas. Aunque no se detectó estacionalidad en los marcadores tróficos de S. thompsoni, A. bathyproctus mostró una dieta predominantemente carnívora a finales de verano en comparación con finales de otoño, más basada en el omnivorismo. Los valores de los lípidos en S. thompsoni fueron más de tres veces mayores en otoño respecto al verano, mientras que los de A. bathyproctus eran prácticamente los mismos. Se sugiere que este cnidario tiene una estrategia trófica ligada a la llegada a pulsos (intermitente) de alimentos, detectándose un claro patrón trófico estacional. La última pregunta propuesta en la presente Tesis es el efecto potencial del cambio climático en la ecología trófica de varios organismos bentónicos (detritívoros y alimentadores de suspensión) en el área de Larsen, un sitio recién abierto al ciclo estacional de la productividad primaria en la Península Antártica, debido al colapso de la barrera de hielo permanente. El estudio de nueve organismos bentónicos (Ophiura carinifera, Ophioperla koehleri, Ophionotus victoriae, Pyura bouvetensis, Cnemidocarpa verrucosa, Primnoisis sp., Protelpidia murrayi, Bathyplotes fuscivinculum y Molpadia musculus), mostró un gradiente en el origen de los alimentos potencialmente disponibles. Cuando comparamos la zona de Larsen (donde recientemente ocurrió la desintegración de la capa de hielo) y la Península Antártica (que nunca tuvo la plataforma de hielo) en verano de 2011, el material sedimentado tiene diferentes valores relacionados con la caída más o menos reciente de la producción primaria (y su abundancia). El material sedimentado es potencialmente parte de la dieta, pero no se encontró una relación directa cuando se analizaron los isótopos estables o los ácidos grasos del sedimento y de los organismos que se alimentan directa o indirectamente de él. Los organismos muestran una dieta omnívora y algunos de ellos incluso una típica dieta carnívora, basada en material reciclado en las zonas Larsen estudiadas, lo que indica que el sistema está en un claro proceso de sucesión y transformación. Dependiendo de la estrategia alimentaria, hubo considerables diferencias en la capacidad de almacenar reservas en forma de lípidos, siendo las especies vágiles las que acumulan menos reservas (lípidos). Se deduce gracias al presente estudio que estas herramientas pueden ser muy útiles para entender cómo la sucesión de las diferentes etapas de una zona transformada por el cambio en la cubierta de hielo afectará a la ecología trófica de los organismos epibentónicos. Todos los resultados han contribuido a una mejor comprensión de la ecología trófica de la comunidad bentónica, y sus estrategias para sobrevivir en un panorama de cambio climático que modifica rápidamente las comunidades, especialmente en las zonas más afectadas, como la Península Antártica.
Antarctica is a frozen continent surrounded by the sea with a deep continental platform characterized by constantly low temperatures. The seasonality of light and ice cover is responsible for the increase of the primary production of phytoplankton in spring-summer and the vertical flux of particulate organic matter (POM), composed by living fresh phytoplankton, faecal pellets and detritus. Suspension feeders and other sessile and vagile organisms have adapted their feeding strategies to these POM pulses. These organisms compose a highly diverse benthic community, regardless their original food source is either similar or not. The rather constant environmental conditions and the high productivity in the spring and summer seasons allow different morphological, feeding, energy storage and reproductive strategies, expressed in a highly diverse macrobenthic assemblages. The relationship of these benthic organisms and food dynamics is very complex and largely unknown, having multiple variants. Together with the deep-sea ecosystems, Antarctic and Arctic polar benthic ecosystems are difficult to reach, but the study of benthic-pelagic coupling is necessary to understand how Antarctic ecosystems will tolerate the ongoing transformation due mainly to the rapid climate change detected in some areas. It is vital to understand the trophic relationships, what are the sources of organic matter to the diet of the benthos and how the organisms acquire and invest the energy as a function of their trophic level. The main objective of this work was studying the variations of the spatial-temporal response of benthos to the availability of organic matter changes, examining the environmental characteristics and their effects on the benthic communities in the Weddell Sea (Eastern Weddell Sea - Austassen-Kapp Norvegia and Antarctic Peninsula - the Bransfield Strait and Larsen A, B and C). In order to hypostatize this study, a combination of trophic markers was used, such as: stable isotopes, fatty acids, and biochemical balance (protein-carbohydrate-lipid). These markers integrate trophic signals, allowing a spatial and temporal comparison of organic matter accumulation and energy storage in benthic suspension feeders. The trophic ecology of sixteen representative species of benthic invertebrates was studied and producing a better interpretation of benthic-pelagic coupling of the still poorly known ecosystem. The seven species of gorgonians (Primnoisis sp, Fannyella nodosa, Ainigmaptilon antarcticum, Notisis sp., Primnoella sp., Dasystenella sp. and Thouarella sp.) collected in the autumn of 2000 in Austasen, showed almost the same values of stable isotopes derived from the phytodetritus in the so called "green carpets" and the microzooplankton. The diet seemed to be based on sunk and re-suspended material, supporting the hypothesis that some suspension feeders deal successfully with the Antarctic winter thanks to this long-lasting food source. The biochemical balance indicated a different energy storage depending on the species and possibly its reproductive traits. To understand the role of seasonality in benthic communities, the trophic ecology of the Alcyonarian Anthomastus bathyproctus in the late autumn 2000 and late summer 2011 in the Antarctic Peninsula was investigated. The main prey (the tunicate Salpa thompsoni) was considered in both seasons to understand its role in the energy budget and preferences of this passive suspension feeder. The main preys of the Alcyonarian were different when both seasons were compared. Although no seasonality was detected for S. thompsoni trophic markers, A. bathyproctus showed a predominantly carnivorous diet in late summer compared to late autumn, in which the signals belonged to a more omnivorous diet. The lipid values in S. thompsoni were more than three times higher in autumn than in summer, whilst those of A. bathyproctus were practically the same. A food pulse trophic strategy is suggested for this cnidarian, detecting a trophic seasonal pattern. The last question proposed in the present Thesis is the potential effect of climate change in the trophic ecology of several benthic organisms (detritivores and suspension feeders) in the Larsen area, a recently opened to the considered normal cycle of the primary productivity in the Antarctic Peninsula due to the permanent ice shelf collapse. The study of nine benthic organisms (Ophiura carinifera, Ophioperla koehleri, Ophionotus victoriae, Pyura bouvetensis, Cnemidocarpa verrucosa, Primnoisis sp., Protelpidia murrayi, Bathyplotes fuscivinculum and Molpadia musculus), showed a gradient of food sources comparing the area of Larsen (where recent disintegration of the ice cover occur) and the Antarctic Peninsula (which never had ice shelf) in summer of 2011. The sedimented material was potentially part of the diet, but not a direct relationship between the sediment and the organisms on stable isotopes or fatty acids markers was found. The organisms show an omnivore diet and some of them even present a typical carnivorous diet, based on non-fresh or reworked material in the Larsen areas studied, indicating that the system is in a clear successional process. On the other hand, depending on the feeding and life style strategy, there were considerable differences in the ability to store reserves in the lipids form, being the vagile species those that apparently accumulate less energy storage reserves (lipids). The present study indicates that these tools may be very useful to understand how the different succession stages of a transformed area due to the change in ice cover will affect the trophic ecology of the epibenthic organisms in the White Continent. All the results contributed to a better understanding of the trophic ecology of the benthic community and their strategies to survive in a climate change panorama that has been rapidly and significantly changing those communities in the last decades, especially in the most affected areas like the Antarctic Peninsula.

The present work focuses on different aspects related to the Antarctic seaweed. As the main primary producers of the coastal areas of Antarctica, this group of organisms play a key role in shaping the biological communities and the ecological dynamics of Antarctic shores. However, compared to other groups of Antarctic organisms or the seaweed communities of other regions of the world, Antarctic macroalgae remain less studied. This is especially true in several areas of knowledge as their actual biodiversity, their evolutionary history and patterns, some aspects of their ecology or the total extent of their relations with other Antarctic organisms and their environment. Aiming to address the lack of knowledge of these areas, we aimed to extend it by focusing our work in several key aspects of Antarctic seaweed biology. As so, we tried to respond several specific questions regarding the topics above mentioned. In this context, we studied biodiversity of seaweed communities that are present in the South Shetland Islands. For that, we tried to identify the composition and influencing factors of the seaweed assemblages present in Deception Island. We also studied how seaweed biodiversity affects Antarctic epiphytic diatoms richness, studying the composition of them, both from Deception and Livingston islands. Moreover, we tried to expand the data with evolutionary relevance by analysing the nuclear DNA content and ploidy levels (C values), as well as the nuclear developmental patterning of some common Antarctic seaweed species with no previous data for those characters. This was achieved by using a fluorimetry technique that sets a reference for comparison for future studies on those parameters. Additionally, we condensed the latest knowledge on the chemical ecology of seaweeds and other organisms from Antarctica, and tried to expand it by investigating the potential antimicrobial activity of these seaweeds. For this, we tested their natural extracts against several Antarctic microorganisms and identified several species that were active chemically. Also, we tested the same extracts for antimicrobial action against several microorganisms that are common human pathogenic surrogates and identified potential human interest in these seaweeds on the search for new sources of antibiotics. Finally, we reported our findings on the role seaweed have in the context of climate change in the Antarctic region. Those findings include the identification of non-native kelp rafts that arrived to the maritime Antarctica, and presented several passenger species that have potential invasiveness in the Antarctic. Regarding that, we classified and explored the possible roles that the rafts themselves and the species travelling with them may play in futures scenarios of climate change in Antarctica.

Ice disturbance is frequently cited as having a major role in structuring benthic communities in shallow polar waters, and yet comprehensive field studies on the direct effects of ice disturbance are rare. This thesis aimed to describe the role of ice disturbance in determining benthic community structure at sites around Rothera Point, Adelaide Island (67° 34.5' S, 68° 07.0' W). The work comprised of two main components; a range of observational studies to describe the general effects of ice disturbance, and an experimental quantification of the disturbance pressure, which was then used to make novel links between disturbance and community structure. A photographic survey using depth transects (0-35 in depth) at three sites showed that benthic assemblages changed continuously along a bathymetric gradient. Assemblages were most patchy at shallow depths and the relative abundance of sessile forms increased with depth, which suggested that disturbance intensity was greatest in the shallows. The immediate effects of iceberg impacts were also investigated. Communities within newly formed iceberg scours were sampled and compared with those in undisturbed areas; scoured assemblages were 95% lower in mean macrofaunal abundance and 75.9% lower in species richness. The recovery of three scour assemblages was monitored for -30 months following the disturbance event. Scoured assemblagesb ecame increasingly similar to undisturbed assemblages over time and marked spatial variability was observed in both scoured and unscoured zones. Experimental markers were designed to detect iceberg impacts and were deployed as 24 grids at four depth increments and two study sites. Markers were surveyed regularly for two years to quantify the frequency of iceberg impacts, which varied significantly with depth, site, season and year. The intensity of disturbance was greatest in the shallows (0-5 m depth) and significantly reduced at 25 m depth. Variation between site and season could be largely explained by the duration of winter fast ice. Extensive sampling at each of the disturbance grids showed that disturbance intensity has a significant and wide-ranging influence on macrobenthic community structure.

This thesis describes the first regularly resurveyed study of marine benthic colonisation processes at a location within the Antarctic Circle (660 30' S). Invertebrate assemblages on hard substrata were studied at 8 m and 20 m depths at three locations near Rothera Point, Adelaide Island (670 34' S, 68° 07' W). Assemblages on natural substrata were surveyed photographically and by sampling of cryptic sessile fauna. Recruitment to upper and lower surfaces of artificial substrata was monitored at monthly intervals through 1.5 yr and subsequent survival and growth of sessile assemblages was monitored photographically over 3 yr. Planktonic larvae of benthic invertebrates were surveyed at monthly intervals through 1.5 yr. Recruitment took place throughout the year but was strongly seasonal in most taxa. Many sessile taxa recruited during winter; apparently in direct contrast to a general pattern of summer recruitment in temperate latitudes. All vagile taxa, by contrast, recruited in summer, regardless of developmental type or time of spawning. Rates of assemblage development, and maximum growth rates of individual species, were slow compared with temperate latitudes but a biotic and biotic disturbances caused realised growth rates to be highly variable at scales of m - km. Ice impacts affected substrata at 8 m but the establishment of assemblages at both depths was controlled principally by postsettlement mortality from biotic disturbances, particularly grazing by the urchinSterechinus neumayeri. Larvae were present in all months but most taxa showed strong seasonality of occurrence. Diversity of larval types was comparable with data from other Antarctic and temperate studies but abundances were higher than in a similar study at Signy Island (60043' S, 45° 36' W). The range of larval types, durations, and times of spawning argues against any strong selective pressures acting on developmental mode itself. Rather, the timing of settlement appears to be the characteristic of the life cycle that is most strongly selected for. It is suggested that differences between sessile and mobile taxa in the timing of settlement may be caused by the seasonal availability of food types for juvenile stages.

This study used Jumbo Piston Core 126, collected from the Nathaniel B. Palmer during cruise NBP10-01, to investigate environmental variability in Barilari Bay, western Antarctic Peninsula as part of the LARsen Ice Shelf System, Antarctica (LARISSA) project. A total of 107 samples were collected every 20cm from a 21.42m sediment core. Benthic foraminiferal data from Jumbo Piston Core 126 was analyzed using Principal Component (PC), Canonical Correspondence Analysis (CCA), and cluster analyses to assist in the Holocene oceanographic and climatic interpretation of Barilari Bay. The first three principal components explain 79.5% of the variance in the foraminiferal abundance data. PC1 comprises 49.6% of the variance and represents the Bulimina aculeata assemblage. PC2 and PC3 explain 16.3% and 13.6% of the variance and characterize the Fursenkoina fusiformis and Pseudobolivina antarctica assemblages, respectively. F. fusiformis assemblage represents the presence of a less saline water mass associated with ice shelf decay. The agglutinated P. antarctica assemblage is indicative of Hyper Saline Shelf Water (HSSW). TheB. aculeata assemblage is associated with Upper Circumpolar Deep Water (UCDW) (Ishman and Domack, 1994) Sediments from ~1100-950 calibrated years Before Present (cal. yr BP) are characterized by theB. aculeata assemblage, indicating the presence of UCDW. At ~950 cal. yr BP the UCDW receded coincident with glacial conditions observed during what is interpreted as the Little Ice Age. The ~950-350 cal. yr BP interval represents glacial conditions interpreted from the high PC scores of the P. antarctica assemblage and low foraminiferal abundances due to HSSW and a high sedimentation rate from glacial runoff. Intermittent pulses of UCDW are observed in the 950-350 cal. yr BP interval, expressed by the PC peaks in the B. aculeata assemblage. Between ~300 and 100 cal. yr BP the middle of the fjord was dominated by the F. fusiformis assemblage, suggesting ice shelf decay and open marine conditions. At ~50 cal. yr BP UCDW progressed back into Barilari Bay and is currently the dominant water mass.

Esta tesis cubre diferentes aspectos de los invertebrados marinos bentónicos de la Antártida. Se trata de una tesis multidisciplinar presentada en formato artículos en la que se hacen las siguientes aportaciones: (i) por un lado se hace una revisión de los productos naturales de origen animal y vegetal descritos hasta Mayo de 2007 en las aguas de la Antártida. En dicha revisión se hace especial énfasis en el papel que juegan los productos naturales en el contexto de su ecosistema; (ii) se aportan también datos sobre experimentos de repelencia alimentaria en los que se utilizaron extractos lipofílicos de invertebrados bentónicos de 2 zonas muy poco estudiadas (este del Mar de Weddell e Isla de Bouvet). En dichos experimentos, que se llevaron a cabo utilizando depredadores simpátricos, se ha demostrado que algo más de la mitad de los invertebrados testados poseen defensas químicas que los defienden frente a posibles depredadores. En algunos de estos casos las defensas químicas parecen localizarse en las partes más expuestas/vulnerables de los organismos testados; (iii) uno de los artículos de esta tesis confirma el potencial antitumoral que tienen los invertebrados marinos bentónicos antárticos y sub-antárticos. Se trata del estudio antitumoral más grande que jamás se haya hecho en este área con resultados muy prometedores para phyla como Chordata, Porifera y Cnidaria, entre otros; (iv) por último se describen un total de 4 nuevas especies de anélidos poliquetos de las aguas someras de la Antártida. Dichos organismos pertenecientes a las familias Cirratulidae (1 especie del género Cirratulus), Dorvilleidae (2 especies del género Ophryotrocha) y Siboglinidae (1 especie del género Osedax), fueron descritos a partir de huesos de ballena colocados experimentalmente en las aguas de Isla Decepción (Islas Shetland del Sur). Estos hallazgos confirman la importancia que los huesos de ballena pueden tener en el contexto de las aguas de poca profundidad de la Antártida.
The Thesis entitled “Antarctic marine benthic invertebrates: chemical ecology, bioactivity and biodiversity" covers different aspects related to Antarctic marine benthic invertebrates. This is a multidisciplinar thesis comprising several scientific papers making the following contributions: (i) on the one hand it revises the described Antarctic marine natural products derived from animals and algae up to May 2007. In this revision, special emphasis is given to the role that these natural products play in their ecosystem; (ii) this thesis also provides data from feeding repellent experiments using lipophilic extracts from benthic invertebrates from two poorly known areas (eastern Weddell Sea and Bouvet Island). These experiments, carried out using sympatric predators, showed that more than half of the invertebrates tested possess chemical defenses against possible predators. In some of the cases, these defenses seem to be located in the most exposed/vulnerable parts of the organisms; (iii) one of the papers included in this thesis confirms that marine benthic invertebrates from Antarctic and sub-Antarctic waters have an interesting antitumoral potential. This work is the largest carried out in the area with very promising results for phyla such as Chordata, Porifera, and Cnidaria, among others; (iv) finally, this thesis comprises the description of 4 new species of annelid polychaetes from the Antarctic waters. These organisms belong to the families Cirratulidae (1 species from the genus Cirratulus), Dorvilleidae (2 species from the genus Ophryotrocha) and Siboglinidae (1 species from the genus Osedax), which were described from whale bones experimentally deployed in Deception Island (South Shetland Islands). These findings confirm the importance that whale bones may have in the Antarctic shallow-waters context.

Univ., Diss.--Bremen, 2003.
Color version at: http://elib.suub.uni-bremen.de/publications/dissertations/E-Diss552_Teix2003.pdf. Enth. 3 Originalpublikationen. Parallel als elektronische Ressource im Fernzugriff verfügbar.

Benthic organisms inhabiting the shallow waters of the Southern Ocean are considered excellent models to study evolutionary processes, population connectivity patterns, and adaptation. They have evolved in an extreme environment, with expanding and retreating periods following glacial cycles, in an alternation pattern. Repeated rounds of population fragmentation in glacial refugia during glacial cycles followed by expansions and secondary contacts during interglacials were the main evolutionary force that brought Antarctic shallow-water ecosystems to their current state. In my PhD dissertation I have investigated in detail these singular evolutionary histories left in the genomes of our target species. Besides the past geological events, currently, threats from global warming arrive to the isolated southernmost continent. Indeed, coastal waters off West Antarctica are some of the most affected oceanic regions of the planet by global warming, with rather pessimistic projections for the near future. Considering this and the increasing local threats to which shallow-water ecosystems are exposed, it is fundamental to develop a well-connected network of Marine Protected Areas (MPAs) throughout the Southern Ocean. Despite genetic connectivity is not usually considered in MPA planning, population genetic studies can provide extremely valuable information to design connected MPA networks. In my dissertation I have also disentangled gene-flow patterns of Antarctic shallow-water benthic invertebrates, aiming to help to improve the current status of Southern Ocean MPAs. In order to achieve my goals, I combined information coming from ‘traditional’ genetic markers, single nucleotide polymorphisms (SNPs) derived from restriction-site associated DNA sequencing (ddRADseq), transcriptomes, and draft-level genomes. A wide range of species presenting different reproductive modes was selected in order to test whether this factor plays a role on connectivity and evolutionary patterns in the explained scenario of glacial alternations: the brooding congeneric nemerteans Antarctonemertes valida, A. riesgoae, and A. unilineata; the demosponges Dendrilla antarctica and Mycale acerata, which present lecithotrophic larvae; and the annelids Pterocirrus giribeti (new species described in the Chapter 1 of my PhD dissertation) and Neanthes kerguelensis, that presumably presents planktotrophic larvae. Our results regarding the evolutionary history of our target species revealed different glacial-refugium strategies independent of their reproductive mode, and generalised signals of bottleneck events. Moreover, blurred species boundaries were detected for the Antarctonemertes lineages, with a central role of glacial cycles in their introgressive evolutionary history. Additionally, we identified adaptive genes for particular glacial-refugium strategies and for the rise of prezygotic barriers during speciation and reinforcement events. Our connectivity results confirmed that genetic connectivity in the Southern Ocean is not determined by a priori dispersal abilities resulting from different reproductive strategies. We revealed an overall high gene flow along the Western Antarctic Peninsula (WAP), which is particularly exceptional for sponges and brooding species. Interestingly, loci under divergent selection were identified for D. antarctica despite admixture, broadly differentiating between the populations of Northern and Southern WAP. We suggest that ongoing natural selection is governed by differences in sea-ice extent and duration, exhibiting the vulnerability of the WAP benthic ecosystems due to the decline in the sea ice predicted for the near future. Finally, we demonstrated that long-distance connectivity did not surpass the regional WAP scale, supporting the implementation of an MPA covering the WAP and the coastal waters off the South Orkneys. Overall, the studies presented in my PhD dissertation represent a step forward in understanding global forces and processes affecting the evolutionary history of Antarctic marine organisms. We illustrated the adaptability of shallow-water benthic invertebrates to the natural changes of the Southern Ocean, while manifesting their vulnerability to future global warming. Remarkably, we highlight the importance of using population genetic data of various benthic invertebrate species to implement MPA networks in one of the most threatened areas of the planet by global warming. The results of my thesis will be fundamental to address the suitability and effectiveness of an MPA network comprising the already implemented MPA at South Georgia and South Sandwich Islands and the proposed MPA covering the WAP and the South Orkney Islands, essential for the survival of Antarctic marine ecosystems.

The Cape Horn Biosphere Reserve, within the remote Sub-Antarctic ecoregion is a reservoir of expressions of biological and cultural diversity. Although it is considered one of 24 wilderness areas remaining in the world, it is not free from local and global threats, such as invasive species, and climate change. Field biologists and philosophers associated to the Sub-Antarctic Biocultural Conservation Program and the Omora Ethnobotanical Park, have worked to describe the region’s biocultural diversity, linking ecological and philosophical research into education, ecotourism, and conservation, through a methodology called field environmental philosophy (FEP), which integrates ecological sciences and environmental ethics through a 4-step cycle consisting of: 1) interdisciplinary research; 2) composition of metaphors; 3) design of field activities with an ecological and ethical orientation; and 4) implementation of in situ conservation areas. In this context, the purposes of this dissertation were to: 1) provide a comprehensive review of publications regarding the conservation status of aquatic and terrestrial insects at a global scale and with an emphasis in southern South America; 2) study the distribution of benthic macroinvertebrates through the sharp altitudinal gradient of the Róbalo River watershed; 3) describe the life histories of Gigantodax sp (Simuliidae: Diptera) and Meridialaris chiloeense (Leptophlebiidae: Ephemeroptera) in the Róbalo River and to assess the potential effects of climate change on their phenology; and 4) to apply FEP methodology in order to better understand and communicate the intrinsic and instrumental values of freshwater invertebrates in the Cape Horn Biosphere Reserve.

The inhabitants of marine benthos must combat the ecological pressure caused by predation, competition and fouling through a series of mechanisms, one of which is chemical defense. This type of protection is particularly extended among sessile and/or sluggish organisms, such as sponges, soft corals or ascidians. The strategies to prevent predation are related to bad taste rather than to toxicity. Moreover, they must be considered along with nutritional quality, since the more nutritious the prey, higher quantities or more potent repellents are needed to gain protection. The production of defensive secondary metabolites is energetically expensive. For this reason, the Optimal Defense Theory (ODT) predicts that defenses must be allocated in the most valuable or more exposed structures or body-regions. In Antarctic communities, the main predators are asteroids, and defensive agents are hence expected to accumulate in superficial layers of potential prey. But dense populations of amphipods, which associate opportunistically with biosubtrata, obtaining both refuge and direct or indirect sources of nutrition, are also very influencing on these bottoms. It has been reported that chemical defenses are very common in Antarctic organisms, in accordance with our results. However, the research effort has not been the same for all the groups, and there are still many aspects to learn on the chemical ecology, like the identification of the implicated products, their mode of functioning or their localization and origin. This PhD has focused on three relevant groups of the Antarctic benthos, quite understudied: hexactinellid sponges, soft corals and colonial ascidians. Two influencing sympatric predators were selected, the sea star Odontaster validus, which is a known model predator, and for the first time, the amphipod Cheirimedon femoratus, used to perform feeding experiments for the detection of repellent chemical defenses. We designed a new protocol which provided numerous methodological profits, as well as a remarkable discriminatory potential for unpalatable activities. In a survey with 31 species of Antarctic organisms, a larger incidence of unpalatable activities was recorded towards C. femoratus than against the asteroid, especially in algae and sponges, in which amphipods may particularly influence defenses distribution for representing potential host-preys. Some organisms instead, seemed to exploit alternative defensive strategies. The ecological success of the three studied groups is probably related to the presence of chemical defenses. In hexactinellid sponges these are weak, yet compensated with a low energetic content, and derive from primary metabolites, such as steroid derivates. Some glucosphingolipids instead, could have a chemotaxonomical value as chemical markers in rossellid sponges. In soft corals, chemical protection is obtained from products originating from both, primary (wax esters) and secondary metabolism (sesquiterpenoids), which seem to cooperate in an additive way, and are likely exuded within the coral mucus in living specimens. The use of primary metabolites for defense represents an effective energy saving strategy. In colonial ascidians, defensive secondary metabolites of terpenoid and alkaloid nature with potent bioactivities predominate, and in some species these are accumulated in internal tissues. Presumably, this distribution is related to the production of chemically defended lavae. Some bioactive secondary metabolites isolated from various sources, like the meridianins, may suggest a broad evolutionary retention, or a symbiotic origin. Regarding bacterial antifouling, ascidians exhibited poor activity, while some soft corals did display inhibition. With this work we provide the identification, localization, and possible origin of several defensive agents in three relevant groups of Antarctic benthic invertebrates.
Los habitantes del bentos antártico combaten la depredación, la competencia y el recubrimiento desarrollando mecanismos como la defensa química. Ésta estrategia está particularmente extendida entre organismos sésiles y organismos de cuerpo blando. Las defensas repelentes contra depredadores han de considerarse junto con la calidad nutricional, pues las dietas muy energéticas enmascaran la repelencia. La producción de metabolitos secundarios defensivos es costosa. Por ello, la Teoría de Defensa Optimizada (ODT) prevé que han de localizarse en las regiones corporales más valiosas o expuestas. En las comunidades antárticas los principales depredadores son las estrellas de mar y se postula la concentración de defensas en áreas superficiales en las presas. Pero también influyen las poblaciones de anfípodos asociados a los biosustratos, obteniendo en ellos refugio y fuente de alimentación. Esta tesis se centra en las defensas químicas de tres grupos relevantes del bentos antártico relativamente poco estudiados: esponjas hexactinélidas, corales blandos y ascidias coloniales. Se seleccionaron dos depredadores simpátricos, la estrella Odontaster validus y, por primera vez, fue utilizado el anfípodo Cheirimedon femoratus. Diseñamos un nuevo protocolo con numerosas ventajas metodológicas además de un gran potencial discriminatorio, y observamos que en 31 especies hubo mayor repelencia hacia el anfípodo que hacia la estrella, sobretodo en algas y esponjas, que podrían representar potenciales huéspedes-presa. A partir de aquí estudiamos muestras de los tres grupos seleccionados. En hexactinélidas, las defensas químicas son más débiles y derivadas del metabolismo primario, pero compensadas con un bajo valor nutricional. Algunos glucoesfingolípidos, podrían tener valor quimiotaxonómico como marcadores de la familia Rossellidae. En corales blandos existen metabolitos de defensa primarios y secundarios operando sinérgicamente, y probablemente forman parte del mucus superficial. En ascidias coloniales, los metabolitos defensivos son secundarios y muy potentes; además, en algunas especies éstos tienden a acumularse en tejidos internos, presumiblemente para producir larvas protegidas químicamente. Las ascidias mostraron poca actividad antibacteriana, pero algunos corales exhibieron respuestas inhibitorias. Esta Tesis proporciona la estructura, distribución y posible origen de los metabolitos responsables de las actividades defensivas en tres grupos relevantes de invertebrados antárticos.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ
Nos últimos anos observa-se um aumento crescente das atividades humanas, tanto científicas quanto turísticas, no ambiente antártico, sendo motivo de preocupação considerando-se que a Antártica é um ambiente de lenta recuperação. Ainda são escassos os estudos sobre o estabelecimento de relações entre a presença de contaminantes e seus efeitos na biota antártica. A contaminação pode ocorrer por processos antrópicos ou naturais e os efeitos destes impactos podem ser detectados e monitorados através da análise das alterações nas comunidades bentônicas. Estas comunidades podem ser consideradas boas indicadoras de impactos ambientais, já que possuem uma relação direta com a origem dos contaminantes acumulados nos sedimentos. Este trabalho avaliou os níveis de metais-traço encontrados no sedimento e em duas espécies circumpolares da megafauna bentônica antártica, a estrela-domar Odontaster validus e o molusco bivalve Laternula elliptica, com a finalidade de determinar se as mesmas podem ser utilizadas como indicadoras de impacto ambiental. Durante o verão austral de 2005/2006 foram realizadas coletas através de diferentes procedimentos, entre 15 e 40m de profundidade, em cinco estações dentro da Área Antártica Especialmente Gerenciada da Baía do Almirantado, Ilha Rei George: 1) Estação Antártica Comandante Ferraz; 2) Botany Point; 3) Punta Ullman; 4) Punta Plaza e 5) Refúgio II. Os seguintes metais foram quantificados tanto para o sedimento quanto para os organismos: Al, V, Cr, Mn, Fe, Ni, Cu, Cd, Ba, Pb e Zn. A concentração de metais variou entre os diferentes compartimentos corpóreos analisados. Para a espécie O. validus, as maiores concentrações de metais-traço (Mn, Ni, Cd, Ba, Pb) e do macronutriente Al, foram encontradas na parede do corpo. Cu, Cr, V e Zn apresentaram maior concentração no estômago, enquanto o macronutriente Fe concentrou-se preferencialmente nos cecos pilóricos. Para a espécie L. elliptica, as maiores concentrações de metais-traço (Mn, V, Ba, Cu) e dos macronutrientes Fe e Al, foram encontradas no sifão. Cd, Ni, Pb e Zn apresentaram maior concentração no rim enquanto o Cr foi mais concentrado no compartimento restos. A concentração de elementostraço nos compartimentos corpóreos de O. validus e L. elliptica não foi influenciada pelo tamanho do organismo (peso total do indivíduo).
Once the Antarctic environment has low recovery rates, the recent growth in the touristic and scientific activities is a serious issue for the scientific community. Few studies have tried to establish the links between the presence of contaminants and the antarctic biota. The contamination may be related to human or natural processes, and be monitored trough the benthic communities. These communities have a direct relation with the contaminants sources in the sediment. The present work analyzed the trace-metals levels found in the sediment and two circumpolar benthic megafauna species in Antarctica, the starfish Odontaster validus and the Antarctic clam Laternula elliptica. The objective was to establish if these species can be used as environmental indicators. Five stations was occupied during the austral summer of 2005/2006, between 15 and 40m deep, in the Antarctic Special Management Area of Admiralty Bay, George King Island: 1) Comandante Ferraz Antarctic Base; 2) Botany Point; 3) Punta Ullman; 4) Punta Plaza and 5) Refúgio II. Analyzes were conducted to quantify the presence of Al, V, Cr, Mn, Fe, Ni, Cu, Cd, Ba, Pb and Zn, both in the sediment and organisms. The metals concentrations vary in the different body compartments. Larger concentrations of (Mn, Ni, Cd, Ba, Pb) trace metals and Al macronutrient were found in the body walls of O. validus. Cu, Cr, V and Zn showed larger concentrations in the stomach and the Fe macronutrient in the caeca pyloric. For L. elliptica, larger trace metals (Mn, V, Ba, Cu) and macronutrients (Fe and Al) concentrations were found in the sifon, while Cd, Ni, Pb and Zn showed larger concentrations in the kidney. Cr presented larger concentrations in the remains compartment. The concentrations of trace elements in both O. validus and L. elliptica were not influenced by the body size (total individual weight).

Altitudinal gradients in Sub-Antarctic freshwater systems present unique opportunities to study the effect of distinct environmental gradients on benthic macroinvertebrate community composition and dispersal. This study investigates patterns in biodiversity, dispersal and population genetic structure of benthic macroinvertebrate fauna across an altitudinal gradient between two watersheds on Navarino Island in southern Chile. Patterns in diversity, density, evenness and functional feeding groups were not significantly different across the altitudinal gradient in both the Windhond and Róbalo Rivers. Taxa richness in both rivers generally increased from the headwaters of the river to the mouth, and functional feeding group patterns were consistent with the predictions of the River Continuum Concept. Population genetic structure and gene flow was investigated by sampling the mitochondrial cytochrome oxidase I gene in two invertebrate species with different dispersal strategies. Hyalella simplex (Amphipoda) is an obligate aquatic species, and Meridialaris chiloeense (Ephemeroptera) is an aquatic larvae and a terrestrial winged adult. Contrasting patterns of population genetic structure were observed. Results for Hyalella simplex indicate significant differentiation in genetic structure in the Amphipod populations between watersheds and lower genetic diversity in the Róbalo River samples, which may be a result of instream dispersal barriers. Meridialaris chiloeense exhibited weak population structure but higher genetic diversity, which suggests this species is able to disperse widely as a winged adult.

A Plataforma Oeste da Península Antártica (POPA) é uma região onde a produtividade primária na superfície do oceano apresenta padrões altamente sazonais e considerável variabilidade interanual. A dinâmica do gelo marinho é o principal fator condicionante da produtividade e, por consequência, dos fluxos de matéria orgânica da superfície para o leito marinho. A matéria orgânica particulada depositada, chamada de fitodetrito, forma densas camadas de alimento lábil disponível para os organismos bênticos. Essa relação estreita entre os processos da coluna de água e aqueles que ocorrem no bentos é chamada de acoplamento bento-pelágico. Com o objetivo de avaliar as respostas da macrofauna bêntica aos fluxos e deposição de alimento, foi realizada uma série temporal sazonal de amostragens (novembro/1999 a março/2001) na POPA em três estações de coleta perpendiculares à costa. Cerca de 25.000 indivíduos pertencentes a 22 táxons foram coletados em 15 amostras de box corer (0,25 m2 cada). Mesmo com alguma variação ao largo da plataforma (de 10.886 ind.m-2 (estação A) a 2.326 ind.m-2 (B)), atribuída a diferenças na topografia, a macrofauna apresentou pouca variabilidade em termos de composição e abundância ao longo do período estudado. Além disso, diferenças na composição e abundância entre estratos sedimentares também foram notáveis, sendo que 90% dos indivíduos foram encontrados entre 0 e 5 cm. Dentre as 185 espécies identificadas, Aurospio foodbancsia (Polychaeta, Spionidae), uma espécie típica de regiões de plataforma na Antártica, mas muito próxima da espécie de mar profundo A. dibranchiata, foi a espécie dominante em todos os períodos e estações (2.087 ind.m-2). Além de Polychaeta, outros grupos abundantes na POPA foram Bivalvia, Tanaidacea e Oligochaeta. Picos de abundância foram observados para algumas espécies, provavelmente associados a eventos sazonais de recrutamento, porém nem sempre associados à chegada do alimento ao fundo marinho da região. Os grupo funcionais de Polychaeta também não variaram ao longo do período estudado, o que indicou que animais depositívoros de superfície e subsuperfície se alimentam ao longo de todo o ano, aproveitando o alimento que permanece lábil e disponível, mesmo no inverno, quando o fluxo de matéria orgânica para o bentos é mínimo. Os resultados encontrados neste trabalho confirmam os resultados já encontrados dentro do projeto FOODBANCS, que a macrofauna da POPA age como um filtro, respondendo menos às flutuações sazonais.
The West Antarctic Peninsula shelf (WAP shelf) experiences a high seasonal and interannual variability in surface primary production. Sea ice dynamics is the principal factor controlling productivity and, therefore, the downward particulate organic matter (POM) fluxes. The deposited POM, also called phytodetritus, forms dense layers of available labile food for benthic organisms. This straight relationship between water column and benthic processes is called benthic-pelagic coupling. A seasonal time-series study was conducted between November 1999 through March 2001 in tree sites on WAP shelf, to determine this relationship, specially the benthic macrofauna (> 300 µm) response to the POM flux and its posterior deposition. From a total of 15 box-corer samples (0.25 m2 each), approximately 25,000 macrofaunal individuals were collected, belonging to 22 taxa. Even with some variation along the shelf, ranging from 10,886 ind.m-2 (site A) to 2,326 ind.m-2 (B), the abundance and composition of macrofauna showed only modest seasonal changes. Differences in these parameters were clear between the inner and outer shelves, probably owing to the topography, which was composed of a basin in the innermost region and a flat region, in the offshore area. Differences in abundance and composition between sediment layers were also notable, with 90% of all individuals belonging to the 0-5 cm layer. Among the 185 identified species, Aurospio foodbancsia (Polychaeta, Spionidae), a typical species of Antarctic shelf regions and closely related to the deep-sea species A. dibranchiata, was dominant in all seasons and sites (2,087 ind.m-2). Besides polychaetes, bivalves, tanaids and oligochaetes were also abundant in WAP shelf. Peaks in abundance were observed for some species and this is believed to be related to seasonal recruitment, however not always associated with the availability of food. Polychaete functional groups did not vary along seasons, indicating that surface and subsurface deposit feeders were subsisting on the labile POM along the year, even during the winter, when POM flux to the benthos is extremely low. The results are similar to those obtained in other FOODBANCS works, and indicate that the WAP shelf macrofauna act as a low-pass filter, muting the seasonal water column processes.

Large aggregations of sylasterid corals have been identified throughout the offshore waters of the Antarctic, Sub-Antarctic and South America. These biodiverse regions are interspersed by deep trenches, channels, sedimentary plains and isolated rocky habitat, which may facilitate or inhibit dispersal over evolutionary and ecological time scales. Deep-sea sampling has increased exponentially, across these benthic habitats, due to collaborative projects such as the Census of Antarctic Marine Life (CAML). Consequently, it is now possible to attempt to combine genetic and taxonomic expertise, explore evolutionary relationships and assess this data in relation to environmental change – both past and future. The biogeographic distribution of stylasterid corals is representative of population isolation, based on the discovery of dissimilar species aggregations throughout sampled regions. To further investigate this biogeographic pattern, I sampled all 33 of the known stylasterid species documented from the Antarctic, Sub-Antarctic, South West Atlantic and Patagonian fiord regions across depths (~10 m - > 2000 m), geographic spatial scales (~10 km – 10, 000 km), and habitat types (shelf, slope, seamount and fiords). Genetic relationships were investigated using DNA sequence data from multiple gene regions including: The mitochondrial ribosomal subunit (16S), cytochrome c oxidase subunit 1 (CO1), and the nuclear Internal Transcribed Spacer (ITS). This data was assigned to four research components to determine 1) the biogeographic distribution of Antarctic and Sub-Antarctic stylasterids (n = 33 species, 14 genera). 2) Phylogenetic relationships based on morphology and genetics (n = 12 species, 8 genera). 3) Phylogenetic relationships incorporating the fossil record, to assess the evolutionary history of stylasterid populations in the Drake Passage (n = 7 species, 6 genera), and lastly, 4) genetic and demographic connectivity between populations to inform conservation management regimes (n = 7 species, 4 genera). Morphological taxonomy combined with mitochondrial DNA sequence data produced a well aligned phylogenetic cladogram. The genetic variability seen in stylasterid 16S and CO1 sequences was comparatively higher than other coral and hydrozoan studies, offering potential for these gene regions in DNA barcoding. This has practical implications including the discovery of new species, cataloguing of Antarctic biodiversity and identification of specimens that are impossible to determine by taxonomic means. However, phylogenetic and taxonomic alignment was only achieved through the incorporation of systematic expertise in species identification, and inter-species relationships remain unresolved when compared to the nuclear ITS gene region. Therefore, the incorporation of more gene regions for study, and the use of molecular taxonomy as a complementary tool, rather than a replacement for traditional systematics is recommended for future studies. When the mitochondrial phylogeny was calibrated with the fossil record, phylogenetic topology represented an evolutionary scenario in which stylasterid ancestors’ speciated in the Drake Passage during the Eocene/Oligocene transition boundary from calcite to aragonite sea conditions (~ 34 MYA). The phylogeny also suggests that skeletal bi-mineralogy may have played a central role in the speciation process. The presence of calcite in some genera and literature on the utility of either calcite or aragonite through oceanic time suggest a successional progression toward aragonite mineralogy in response to modern oceanic conditions (Oligocene => modern). Further research in this area may lead to the identification of acclimation states in stylasterid corals, and information on their ability to buffer impending ocean acidification, as the chemical state of the Southern Ocean shifts towards calcite sea conditions in the near future. When investigating genetic population connectivity in the Sub-Antarctic, and across the Polar Front into South America, estimates demonstrate limited to no gene-flow across spatial scales of 300 - > 1000 km. Large scale comparisons were clearly subdivided, and genetic subdivision was evident both among populations either side of, and north of the Polar Front based on CO1 data. However, disparate gene-flow estimates derieved from 16S signify that populations were connected through evolutionary linkages, and connectivity south of the Polar Front may be amplified by the presence of the Antarctic Circumpolar Current (ACC). For fine scale comparision, local estimates of connectivity (~ 200 km) between two Errina spp. fiord populations in Patagonia, Chile, showed no evidence of genetic subdivision (FST = 0, p = 0.6). Similarly, Errina spp in East Antarctica also showed no evidence of genetic subdivision (ITS-1 FST = 0.03 P = 0.165 and ITS-2 FST = 0.002, P = 0.27). However, despite a lack of genetic differentiation in ITS Errina population comparisons, haplotype networks typify a pattern of adaptive radiation from a common ancestor, and upon comparing nucleotide polymorphism in CO1 (π =0.012 – 0.11), 16S (π =0 – 0.05), ITS-1 (π 0 - 0.002) and ITS-2 (π 0.02 – 0.03) it was determined that relative variability in 16S and ITS represented historic connections, whilst CO1 being more variable, may also be more recent. Taken together, results suggest that a multitude of factors influence stylasterid coral populations, and temporal variation is particularly important in the context of this study. It is recommended that researchers focus on contemporary measures of connectivity, preserve specimens with genetic research in mind (> 90% ethanol preservation at the time of collection), and incorporate more loci to test connectivity across multiple spatial scales and species. The potential use of CO1 or 16S as barcoding genes will help in this process. However, until funding towards more deep-sea Antarctic sampling and molecular information emerges, the data presented in this thesis has ascribed a measure of localised geographic segregation, historic isolation and a limited capacity to recover following benthic disturbance. Substantiating that stylasterid corals congregate in diminutive and isolated populations. Therefore, to preempt anthropogenic damage to coral ecosystems, patterns of geographic isolation need to be incorporated into the design of Antarctic Marine Protected Areas (MPAs) - to preserve essential habitat, buffer climate change, mitigate the effects of ocean acidification, and combat localised impacts such as destructive fisheries which pose a direct threat to coral populations, and their associated taxa.

With increasing anthropogenic threats to the marine environment, it has become a priority to improve our understanding and conservation of marine fauna. In Antarctic waters, a rich and diverse benthic fauna thrives. However, the relative isolation of these organisms and their adaptation to the unique Antarctic environment potentially heightens their vulnerability to environmental change. Thorough research on the genetic and ecological structure of Antarctic benthic invertebrate populations is lacking, particularly for some of the most dominant taxa, such as the Amphipoda. This study investigated genetic structure, diversity and population ecology in some common Antarctic benthic amphipod species, to build a more rigorous understanding of the Antarctic benthos that will aid in future management planning. Genetic structure was explored over a circum-Antarctic scale in the widespread amphipod species Eusirus perdentatus and Eusirus giganteus from the continental shelf, using DNA sequences of two mitochondrial regions (COI and CytB) and one nuclear region (ITS2). Phylogenies and haplotype networks provided strong evidence that E. perdentatus harbours two previously undetected cryptic species, and E. giganteus harbours at least three, highlighting our current misunderstanding of Antarctic benthic diversity. There were clear differences in the distribution, genetic diversity and connectivity of populations within each cryptic species, and it is proposed that this reflects different modes of post-glacial recolonisation of the continental shelf. Within one cryptic species, high genetic population differentiation (FST > 0.47, p < 0.01) suggested a potential allopatric speciation process at play. Genetic connectivity was explored over large (1000km) to very fine (100m) distances in the ubiquitous nearshore amphipod Orchomenella franklini, using seven highly polymorphic microsatellite markers. Genetic diversity differed significantly among populations, potentially reflecting local environmental conditions including anthropogenic pollution. Hierarchical AMOVA revealed marked genetic subdivision (FST = 0.16, p < 0.001) across the largest geographical scale and evolutionary isolation of these populations was inferred. Furthermore, three loci showed signs of selection across this scale, providing evidence of locally adapted populations. Gene flow was also restricted at smaller scales, indicating a stepping-stone mode of dispersal consistent with the brooded development of amphipods. The ecology of O. franklini was investigated through length measurements, sex and reproductive status of > 6000 individuals, spatial and temporal patterns in abundance, and corresponding relationships with environmental data. The life history of O. franklini revealed several traits that exemplify adaptation to the polar environment, including delayed reproduction, longevity (> 2 years), and seasonal breeding linked to the summer phytoplankton bloom. There was preliminary evidence of inter-annual and spatial fluctuations in reproductive timing, potentially reflecting local sea-ice conditions. O. franklini was found to reach astounding densities (> 65,000/m2) and abundance was highly heterogeneous in space and time. The distribution of O. franklini was related to various sediment properties although the relationship differed with geographic region, highlighting a close association to the local environment as well as broader Antarctic conditions. This study has provided significant insight into the dynamics of Antarctic benthic amphipod populations over a range of scales. Together the results emphasise a considerable degree of heterogeneity largely overlooked in Antarctic benthic organisms (from the taxonomy of entire species down to local-scale intraspecific population dynamics), and thereby support predictions of their vulnerability to anthropogenicinduced change. Results also shed light on speciation processes in Antarctic waters, and will ultimately help inform future planning decisions regarding spatial management of the Antarctic benthic ecosystem.

The global imperative to sustainably manage deep-sea bottom fisheries and mitigate impacts to benthic habitats is constrained by the limited existing biological data available to inform decisionmaking. Physical surrogacy, where benthic biodiversity is characterised based on its relationship with environmental parameters, was explored as a means of extrapolating the distribution and biomass of benthic species from sample sites to seascapes of the deep-sea. The evaluation of surrogates focused on those benthic species considered most susceptible to disturbance from bottom fishing gears including sponges and corals (termed ‘vulnerable taxa’) and data from the sub-Antarctic Heard and McDonalds Islands (HIMI) region. HIMI hosts an established bottom fishery with protection for biodiversity afforded through a large marine protected area (MPA). However whether the MPA meets CAR principles (comprehensive, adequate and representative) in the context of vulnerable taxa remains largely unknown due to a limited understanding of the HIMI benthic habitats. To readdress the paucity of basic information and provide empirical data with which to develop predictive models, quantitative benthic samples were collected from 104 stations in depths of 200 to 1000 meters and analysed to document benthic biodiversity and community structure across HIMI. Data from HIMI were then used to develop surrogacy methods that were applied to other regions in the deep sea. A total of 312 taxa were recorded in the deep-sea at HIMI. Diversity was dominated by sessile suspension-feeders, including numerous undescribed and possibly endemic taxa, and was similar to other sub-Antarctic islands but lower than rich areas on the continental shelves of Antarctica and Australia. Analyses of assemblage structure using taxa biomass records and the clustering method 'Partitioning Around Medoids' revealed a clear zonation between HIMI’s eastern and western banks, the central plateau, south-facing slopes and waters deeper than 500 m, which was driven mostly by changes in seafloor current speed, temperature and the concentration of particulate organic carbon. Disturbance from bottom fishing was not identified as an important proxy for biodiversity despite extensive trawling for more than 10 years, and instead suggests a strong link between benthos and environmental parameters, highlighting the vulnerability of these communities to changing environmental conditions. Similarly, the restricted distributions of many taxa and levels of endemicity in some groups highlight the uniqueness and vulnerability of the HIMI benthic habitat and importance for conservation. Nonetheless, it was acknowledged that the study failed to sample the most heavily trawled areas at HIMI and that further taxonomic scrutiny (e.g. bryozoans are largely unsorted at this stage) might impact the study conclusions. From empirical data at HIMI, ten vulnerable taxa were selected for which there were sufficient observations for model training (n >50). Four modelling approaches were contrasted to determine an appropriate method to model and predict vulnerable taxa across HIMI using physical surrogates: generalized linear models (GLM), generalized additive models (GAM), boosted regression trees (BRT) and random forests (RF). For each method, two sequential models were constructed; one to predict the occurrence probability of each vulnerable taxa (termed ‘occurrence model’) and one to predict the biomass of that vulnerable taxa given their presence in an area (termed ‘biomass model’). To contrast model performance, data were split into training and test datasets (cross-validation) and predictions evaluated using a series of performance indices relating to accuracy, calibration and bias between observed and predicted values. RF was identified as the preferred method to further explore and predict vulnerable taxa across HIMI due to consistent good performance (i.e. good accuracy, good calibration and low bias between observed and predicted values) and hence predictions were made using this approach. The predictions of occurrence and biomass of vulnerable taxa across the HIMI seascape indicated a higher frequency and biomass in shallow depths (<500 m), and on complex seascape features (e.g. HIMI's banks and craggy slopes), compared with the deeper areas of the plateau. Analysis of predictions using the conservation planning software Zonation highlighted HIMI's banks and numerous areas across the central plateau and continental slope as priority areas for conservation, many of which are currently protected by the MPA. To test the broader applicability of the RF framework, models of vulnerable taxa were subsequently constructed for the continental shelf of East Antarctica (30°E – 150°E) where the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is considering the adoption of a Representative System of MPAs (RSMPA). Like HIMI, the benthos here are poorly described and marine conservation planning may benefit from model estimates to assist decision making. Benthic samples from the region and collocated environmental variables (including sea ice properties) were used to parameterise RF models for eight vulnerable taxa that were classified using the same principles as for HIMI. Both the occurrence and biomass models returned high accuracy according to the indices used, suggesting a high level of confidence in predictions across East Antarctica, and highlighting the transferability of the RF framework to other seascapes. Model estimates revealed a number of hotspots, namely the Prydz Bay region, but also Gunnerus Ridge, west of both Enderby Land and Casey Station and patches between Adelie Land and George V Land, the majority of which are encompassed within the proposed RSMPA. Importantly the model estimates presented in this study suggest that CAR principles have been achieved for vulnerable benthos in the HIMI and (proposed) East Antarctic MPAs. In developing these MPAs, the distribution and hence representativeness of protection for benthic habitats and their biota within the MPA was inferred largely from physical variables as the empirical data required to characterise these habitats were sparse or not available at the time. My predictive modeling results that do incorporate empirical data and have produced similar recommendations for biodiversity conservation at HIMI and in East Antarctica suggest that the use of physical surrogates were an adequate tool for marine planning in the absence of biological data in these systems. More broadly, the results suggest that management or mitigation measures for benthos based on physical parameters may provide adequate precautionary management in other marine ecosystems where the empirical data necessary to evaluate the benthic habitat are lacking. The accuracy of predictions and transferability of the RF framework means that methods developed here might be readily applied to other seascapes where decision-making may benefit from predictions. Sample size, model extent and data resolution were all potential sources of uncertainty which would best be addressed through targeted field sampling and surveys. However given the immediacy of the issue of managing bottom fishing to prevent significant adverse interactions with vulnerable ecosystems, and the practical difficulties associated with obtaining empirical data, surrogate-based management is the only practical means to make reasoned decisions about high seas resource management and for the establishment of a CAR system of MPAs throughout the Southern Ocean.

Sediment runoff accelerated by human activities is known to be a major threat to nearshore marine communities worldwide, however impacts of sedimentation in Antarctica are largely unknown. Each summer at Australia's Casey Station, meltwater entrains sediment from crushed rock roadways causing visible surface plumes in Brown Bay. Observations during previous studies indicated a paucity of reef species in Brown Bay compared to other bays in the Windmill Islands. Differences were attributed to two possible factors: 1) elevated sedimentation rates resulting from human activities, and 2) lower benthic irradiance caused by thicker snow cover overlying sea ice. This thesis examines the potential impacts of sedimentation and benthic irradiance on shallow rocky reef assemblages in Antarctica using both manipulative in situ and aquarium experiments. Digital video transects quantitatively confirmed that reefs in Brown Bay supported a significantly lower cover of biota, fewer total species and individuals, and fewer sponge species compared to nearby 'control' bays. Recruitment to artificial substrata in Brown Bay and 'control' bays was numerically dominated by spirorbid polychaetes and encrusting bryozoan species after 13 and 37 months. Recruitment varied significantly between bays, although overall fewer species and fewer bryozoan species recruited at Brown Bay. More taxa recruited when sedimentation was experimentally inhibited in Brown Bay (using Plexiglas shields), indicating sediment loads were hindering recruitment. Aquarium experiments showed a 0.5 mm thick sediment layer prevented zoospore settlement and early post-settlement growth of the brown alga, Himantothallus grandifolius, and smothering of attached zoospores by a thin layer of sediment caused reduced germ tube growth. Translocated individuals of red alga, Palmaria decipiens, in Brown Bay and 'control bays' had thalli lengths 80 - 99% shorter after 12 and 36 months compared to lengths at initial deployment. Reduced thallus growth was apparent even when sedimentation was artificially reduced, indicating that factors other than sedimentation influence the growth of adult P.decipiens. A clear effect of irradiance levels on thallus growth of this species in the absence of sedimentation was subsequently identified in aquarium experiments, and results correlated with the field observations. Anthropogenically increased sedimentation rates in Antarctica were shown to influence recruitment success of sessile reef taxa (flora and fauna), while benthic irradiance was identified as a strong determinant of macroalgal distribution. Sound environmental management of runoff accelerated by human activities in Antarctica is considered critical for reducing impacts on marine environments, particularly in light of climate change predictions for polar environments.

Mode of access: World Wide Web.
Thesis (Ph. D.)--University of Hawaii at Manoa, 2005.
Includes bibliographical references.
Electronic reproduction.
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x, 202 leaves, bound ill. (some col.) 29 cm

Biodiversity is nature’s most valuable resource. The Southern Ocean contains significant levels of marine biodiversity as a result of its isolated history and a combination of exceptional environmental conditions. However, little is known about the spatial and temporal distribution of biodiversity on the Antarctic continental shelf, hindering informed marine spatial planning, policy development underpinning regulation of human activity, and predicting the response of Antarctic marine ecosystems to environmental change. In this thesis, I provide detailed insight into the spatial and temporal distribution of Antarctic benthic macrofaunal and demersal fish biodiversity. Using data from the George V shelf region in East Antarctica, I address some of the main issues currently hindering understanding of the functioning of the Antarctic ecosystem and the distribution of biodiversity at the seafloor. The focus is on spatial biodiversity prediction with particular consideration given to previously unavailable environmental factors that are integral in determining where species are able to live, and the poor relationships often found between species distributions and other environmental factors. Food is a fundamental requirement of life, influencing the distribution of all animal species, and for species living at the seafloor below the photosynthesis zone, this food derives from surface primary production. In Chapter 2, I present an interdisciplinary approach for modelling the redistribution of food-particles from the ocean-surface to the seafloor, combining satellite-data with an ocean-model, particle tracking, and diatom abundances from sediment grabs for validation. I show that different aspects of the estimated seafloor food-availability link directly to the abundance and richness of key Antarctic seafloor macrofauna observed from camera still-images. I then combine observations from the seafloor, bathymetry, and food-availability estimates to produce a (validated) predictive map of the distribution of important habitat-forming suspension feeders on the George V shelf (Chapter 3). Using a similar approach, in this chapter I also predict strong responses in the abundance of suspension feeders to changes at the ocean surface caused by a major glacier calving event in 2010. Biodiversity has many different attributes. Aside from the abundance of habitat-forming fauna, which is an important proxy for biodiversity, the spatial distribution of single species is also important in determining community structure. However, many species are rare which is why researchers have historically grouped species together based on taxonomic or functional similarity before modelling. Joint-species distribution models can aggregate species based on similarity in their responses to environmental factors, allowing prediction of the spatial distribution of multiple species, including rare species, with higher confidence than other more commonly used statistical methods, and with fewer assumptions regarding associations between grouped species. I use joint-species distribution models for mapping the distribution of diversity and community structure in benthic macro-invertebrates (Chapter 4) and demersal fish (Chapter 5). In chapter 4, I also analyse species-level data of benthic macro-invertebrates that are a-priori aggregated into higher level taxonomic and functional groups of species, and show that aggregating species into higher level groupings leads to increased modeluncertainty (Chapter 4). Comparing patterns in the spatial distribution of demersal fish and benthic invertebrates, I then show that communities of benthic species can be described along four broad habitat types characterised mainly by depth and slope of the seafloor, namely shallow-flat, shallow-steep, deep-flat, and deepsteep environments, with food-availability additionally influencing these habitat distinctions (Chapter 5). In this chapter I conceptualise knowledge about community structure and interactions among functional groups and key environmental drivers in the Antarctic benthic ecosystem in a qualitative network topology, test how differences in the environmental setting affect ecological structure, and validate the dynamic network model results with the mapped distributions of fish and macroinvertebrates, revealing insight into ecosystem functioning. This work shows that the large scale spatial, temporal and structural distribution of Antarctic benthic biodiversity is mainly influenced by depth and slope of the seafloor and by the availability of surface-derived food, which links the seafloor strongly to environmental processes at the ocean-surface. Inclusion of the food-availability models results in more accurate mapping of the spatial and temporal distribution of Antarctic marine biodiversity. The high confidence in the spatial predictions of benthic biota means that the representativeness of future Marine Protected Areas can be better assessed and possible changes in the benthic ecosystem due to environmental or human pressures can be better detected and understood. Future predicted increases in primary production will likely result in higher abundances of benthic suspension feeders and alter community composition, but patterns are variable, even within regions. The advances presented in this thesis can form the basis for future work to map the distribution of Antarctic benthic biodiversity on a circumpolar scale, identify habitats and species assemblages critical for conservation, quantify the total biomass of Antarctic benthic communities, estimate the contribution of Antarctic benthic communities to the sequestration of atmospheric carbon, and estimate how these communities will change in the future based on climate projections. In Chapter 6, I review and discuss how technological and collaborative advances, including those outlined in this thesis, allow us to predict marine biodiversity unlike ever before. The spatial and temporal scales at which predictions are now possible, and the confidence in the predictions themselves, help us to better assess management and policy decisions from local to global scales. These recent developments also allow exploring new ways to predict biodiversity in the future, for the mutual benefit of marine ecosystems and humanity.

This project examined the effects of ecological factors and anthropogenic contaminants on benthic diatom communities near Casey Station, in the Windmill Islands, Antarctica. Preliminary sampling indicated significant compositional differences occurred between diatom communities in bays immediately adjacent to Casey Station and those more distant. Subsequently, a more detailed appraisal of spatial variability in benthic diatom communities was undertaken. Significant differences in community composition were demonstrated for all scales examined, however, increased distances between samples typically corresponded to increased dissimilarity. The influence of environmental factors on spatial variability was assessed using direct gradient ordination techniques. Grainsize, particularly the mud content, accounted for the majority of variation in diatom abundances explained by the measured environmental variables. Differences in light availability, water depth and grain-size explained 60% of the variation in community composition observed between locations. The remaining 40% of the variation in diatom community composition remains unexplained; potential causes include freshwater input, and chemical contamination. A preliminary analysis of temporal variability in benthic diatom communities from the Windmill Islands is presented. Seasonal, short-term (l00's of years) and long term (1000's of years) changes in community composition were examined at several locations. Temporal variability of the diatom communities within Brown Bay was also assessed, in conjunction with metal and Pb210 data. Within one core, a shift in community composition was detected subsequent to the onset of chemical contamination. Some changes in species abundance exceeded the natural variability observed in control cores, and thus were attributable to chemical contamination. Relationships between diatom abundances and concentrations of different metals within Brown Bay were examined using direct gradient analyses. Approximately 50% of the variation in the diatom community composition was related to metal concentrations. Further clarification of the interactions between metals, sediment grain-size and diatom community composition would be required prior to the development of predictive models. Direct gradient analyses also demonstrated a weak correlation between diatom community composition and hydrocarbon distribution. Manipulative field experiments were used to demonstrate that the composition of diatom communities can be influenc.ed by both metal and hydrocarbon contaminants at concentrations comparable to levels produced by station activities. This supports the conclusion that anthropogenic contaminants are responsible for some compositional differences observed in diatom communities, both within Brown Bay and between Brown Bay and reference locations.

"May 2005"
Bibliography: leaves 209-224.
x, 211 leaves : ill. ([1] col.), map ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Environmental Biology, 2005

"May 2005"
Bibliography: leaves 209-224.
x, 211 leaves : ill. ([1] col.), map ; 30 cm.
Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Environmental Biology, 2005