Dissertations / Theses on the topic 'Seagrasses'

Seagrass meadows are highly productive, ecologically and economically valuable ecosystems. However, increased human activities along the coastal areas leading to processes such as eutrophication have resulted in the rapid loss and deterioration of seagrass ecosystems worldwide. This thesis focuses on the responses of seagrasses to increases in nutrients, subsequent increases in ephemeral algae, and changes in the physical-chemical properties of seawater induced by interaction with other marine biota. Both in situ and laboratory experiments conducted on the tropical seagrasses Cymodocea serrulata and Thalassia hemprichii revealed that increased concentrations of water column nutrients negatively affected seagrass photosynthesis by stimulating the growth of the epiphytic biomass on the seagrass leaves. Interaction between seagrasses and other marine organisms induced different responses in seagrass photosynthesis. Ulva intestinalis negatively affected the photosynthetic performance of the temperate seagrass Zostera marina both by reducing the light and by increasing the pH of the surrounding water. On the other hand, the coexistence of mussels Pinna muricata and seagrass Thalassia hemprichii enhanced the photosynthetic activity of the seagrass, but no effect on the mussels' calcification was recorded. This study demonstrates that seagrass productivity is affected by a multitude of indirect effects induced by nutrient over-enrichment, which act singly or in concert with each other. Understanding the responsive mechanisms involved is imperative to safeguard the ecosystem by providing knowledge and proposing measures to halt nutrient loading and to predict the future performance of seagrasses in response to increasing natural and human perturbations.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Papers 1, 3 and 4: Submitted. Paper 2: Manuscript.
Swedish Agency for Research Cooperation (Sida/SAREC) marine bilateral programme

Seagrass beds cover large intertidal and subtidal areas in coastal zones around the world and they are subjected to a wide variety of anthropogenic influences, such as nutrient enrichment due to sewage seepage. This study was undertaken to address specific questions focusing on whether near shore tropical seagrasses that receive a constant influx of groundwater nutrient inputs, would exhibit a higher productivity and to what extent epiphytic algae reflect the impacts of nutrient inputs. An additional aspect of study was to determine the prevalence of “acid zones” in tropical seagrasses. The productivity of the seagrasses Cymodocea rotundata, Thalassia hemprichii and Thalassodendron ciliatum was compared in two sites along the Kenyan coast; Nyali (a high nutrient site) and Vipingo (a low nutrient site). Of the three seagrasses T. hemprichii showed the most distinct differences with higher growth and biomass in the nutrient rich site whereas the growth of C. rotundata was similar in the two sites. A high epiphytic cover was found on the shoots of T. ciliatum found in the high nutrient site Nyali.

Morphological and genetic characterization of bacterial and cyanobacterial epiphytes showed specific associations of nitrogen fixing cyanobacteria on the seagrass C. rotundata in the low nutrient site (Vipingo). At this site, shoots of C. rotundata had a higher C:N ratio compared to shoots in the high nutrient site (Nyali) indicating that the association with nitrogen fixing cyanobacteria is a strategy, for this species, to meet its nutrient needs. Bacterial epiphytes belonging to the group Cytophaga-Flavobacteria-Bacteroides (CFB) were found on T. ciliatum and T. hemprichii from the two sites. CFB bacteria are characteristic of waste water, particularly from livestock farming areas, thereby confirming seepage of groundwater from surrounding catchment areas. These prokaryotic associations were specific for the different seagrasses and it appears that the establishment of epiphytic associations may not be a random encounter but a specific association that meets specific needs.

The seagrass T. ciliatum in the high nutrient site had an abundance of macroalgal epiphytes and the impact of the epiphytic coverage was assessed using Pulse Amplitude Modulated (PAM) fluorometry. The photosynthetic activity of seagrass parts that were covered by epiphytes was suppressed but the productivity of the whole shoot was not significantly reduced. In the nutrient rich site, epiphytes were found to contribute up to 45% of the total estimated gross productivity, during the SE monsoon season, while epiphytic contribution in the nutrient poor site, was 8%. Epiphytic abundance and contribution to productivity decreased during the NE monsoon. The photosynthetic activity of T. ciliatum shoots was similar in the two study sites with shoots in the nutrient rich site growing faster. T. ciliatum, in the low nutrient site, invested in the development of below ground root tissue which may indicate the development of a strategy to gain access to pore water nutrient pools.

Carbon uptake strategies of eight tropical seagrasses were re-evaluated to determine how common the “acid zone” mechanism is among tropical seagrasses. Six of the eight species studied showed photosynthetic inorganic carbon (Ci) acquisition based on carbonic anhydrase catalysed HCO₃^- to CO₂ conversions within an acidified diffusion boundary layer (“acid zone”). Cymodocea serrulata appeared to maintain its carbon uptake by extracellular carbonic anhydrase catalysed CO₂ formation from HCO₃^- without the need for acidic zones, whereas, Halophila ovalis appeared to have a system in which H⁺ extrusion may be followed by HCO₃^--H⁺ co-transport into the cells. These findings indicate that competition for carbon, between the host seagrass species and epiphytes, could determine seagrass-epiphyte associations.

[cat] [cat]Introducció L’ herbivorisme és un procés ecològic clau que regula la composició i l’estructura de les comunitats de plantes i determina la transferència d'energia de productors primaris a la resta de la cadena tròfica. Les plantes han desenvolupat diversos mecanismes de defensa per evitar o resistir l’herbivorisme. Entre ells destaquen les estratègies tolerància, que disminueixen l'efecte de l’herbivorisme en la vitalitat de la planta (ex. acumulació de reserves en teixits subterranis) i les estratègies de resistència, l’objectiu de les quals evitar el consum (ex. augment del contingut en fibra). Aquestes estratègies es basen en característiques morfològiques (ex. duresa) i químiques (ex. defenses químiques) de les plantes i poden expressar-se de forma contínua (constitutives) o en resposta al dany per herbívors (induïdes). L’herbivorisme en el medi marí pot ser major que en sistemes terrestres i pot tenir conseqüències especialment importants quan afecta a espècies formadores d’habitat Les fanerògames marines són espècies fundadores dominants en zones costaneres i que ens proporcionen múltiples i importants serveis ecosistèmics. Com a conseqüència de la seva rellevància ecològica i socioeconòmica, aprofundir en el coneixement de les interaccions planta-herbívor en aquests ecosistemes és crucial, ja que existeixen cada vegada més exemples que indiquen que canvis en les poblacions d'herbívors han suposat importants pertorbacions en aquests ecosistemes. El propòsit principal d'aquesta tesi és entendre com canvis en factors ambientals determinen la variació de les estratègies de defensa i la palatabilitat de la planta, i per tant el comportament dels herbívors. Contingut de la investigació La disponibilitat de nutrients destaca pels seus efectes sobre les característiques químiques i morfològiques de les plantes ja que augmenta el valor nutritiu i disminueix el contingut en fibres de les fulles tant en experiments de fertilització com en regions amb major disponibilitat de nutrients, la qual cosa les pot fer més vulnerables al consum per herbívors. La simulació del dany per herbívors afecta a les estratègies de defensa de les plantes de forma diferent en les dues espècies estudiades. Mentre que en Posidonia oceanica s'indueix la producció de compostos de resistència, en Zostera marina no hi ha inducció, disminuint a més la seva resistència i tolerància. Això es tradueix en què els herbívors prefereixen les fulles més nutritives repetidament retallades de Z. marina i les fulles sense retallar amb menys fibres i més nutrients de P. oceanica. Els canvis ambientals relacionats amb el canvi global analitzats en aquesta tesi (augment del CO2 i de la temperatura), tenen importants efectes en les plàntules de P. oceanica. L'augment del CO2 dissolt augmenta l'activitat fotosintètica de la planta i amb això les reserves de carbohidrats de les llavors. Tot i que l'augment de CO2 disminueix la qualitat nutricional de les fulles, van ser aquestes les preferides pels herbívors, possiblement a causa de l'augment de sacarosa o per altres característiques no analitzades en les plàntules. Contràriament als efectes observats amb l'augment de CO2, l'increment de la temperatura produeix efectes clarament negatius; augmentant la mortalitat, la respiració i l’ús de les reserves de la llavor en aquestes plàntules. A més disminueix el contingut en fibres de les fulles, reduint -se la resistència enfront de l’herbivorisme i augmentant per tant la preferència per herbívors. Aquests resultats mostren els potencials efectes additius que l’herbivorisme pot suposar en els impactes dels canvis ambientals en les poblacions de plantes marines. Conclusió La recerca presentada en aquesta tesi contribueix a entendre els mecanismes que influeixen en els canvis de les estratègies de defensa enfront de l’herbivorisme. Principalment, en com aquests mecanismes canvien sota diferents condicions ambientals i com els canvis en les característiques associades a resistència enfront d'herbívors determinen la vulnerabilitat de la planta enfront de l’herbivorisme. A més, destaca la importància d'avaluar els efectes dels canvis ambientals sobre les interaccions entre espècies.
[spa]Introducción: El herbivorismo es un proceso ecológico clave que regula la composición y estructura de las comunidades de plantas y determina la transferencia de energía de productores primarios al resto de la cadena trófica. Las plantas han desarrollado diversos mecanismos de defensa para evitar o resistir el herbivorismo. Entre ellos están las estrategias tolerancia, que disminuyen el efecto del herbivorismo en la vitalidad de la planta (ej. acumulación de reservas en tejidos subterráneos) y las estrategias de resistencia cuyo objetivo es evitar el consumo (ej. aumento del contenido en fibra). Estas estrategias se basan en características morfológicas (ej. dureza) y químicas de las plantas (ej. defensas químicas) y pueden expresarse de forma continua (constitutivas) o en respuesta al daño por herbívoros (inducidas). El herbivorismo en el medio marino puede ser mayor que en sistemas terrestres y puede tener importantes consecuenc ias cuando afecta a especies formadoras de hábitat Las fanerógamas marinas son especies fundadoras dominantes en zonas someras costeras que nos proporcionan múltiples e importantes servicios. Debido a su relevancia ecológica y socioeconómica, profundizar en el conocimiento de las interacciones planta-herbívoro en estos ecosistemas es crucial pues existen cada vez más ejemplos que indican que cambios en las poblaciones de herbívoros han supuesto importantes perturbaciones en dichos ecosistemas. El propósito principal de esta tesis es entender cómo cambios en factores ambientales determinan la variación de las estrategias de defensa y palatabilidad de la planta, y por tanto el comportamiento de los herbívoros. Contenido La disponibilidad de nutrientes destaca por sus efectos sobre las características químicas y morfológicas de las plantas ya que aumenta el valor nutritivo y disminuye el contenido en fibras de las hojas tanto en experimentos de fertilización como en regiones con mayor disponibilidad de nutrientes, lo cual las puede hacer más vulnerables al consumo por herbívoros. La simulación del daño por herbívoros afecta a las estrategias de defensa de las plantas de forma diferente en las dos especies estudiadas. Mientras que en Posidonia oceanica se induce la producción de compuestos de resistencia, en Zostera marina no hay inducción disminuyendo además su resistencia y tolerancia. Esto se traduce en que los herbívoros prefieren las hojas más nutritivas repetidamente recortadas de Z. marina y las hojas sin recortar con menos fibras y más nutrientes de P. oceanica. Los cambios ambientales relacionados con el cambio global analizados en esta tesis (aumento del CO2 y de la temperatura), tienen importantes efectos en las plántulas de P. oceanica. El aumento del CO2 disuelto aumenta la actividad fotosintética de la planta y con esto las reservas de carbohidratos de las semillas. A pesar de que el aumento de CO2 disminuye la calidad nutricional de las hojas, éstas fueron las preferidas por los herbívoros, posiblemente debido al aumento de sacarosa o por otras características no analizadas en las plántulas. Al contrario que el aumento de CO2, el incremento de la temperatura produce efectos claramente negativos aumentando la mortalidad, la respiración y uso de las reservas de la semilla en estas plántulas. Además, disminuye el contenido en fibras de las hojas reduciéndose la resistencia frente al herbivorismo y aumentando por tanto la preferencia por herbívoros. Estos resultados muestran los potenciales efectos aditivos que el herbivorismo puede suponer en los impactos de los cambios ambientales en las poblaciones de plantas marinas. Conclusión La investigación presentada en esta tesis contribuye a entender los mecanismos que influyen en los cambios de las estrategias de defensa frente al herbivorismo. Principalmente, en cómo estos mecanismos cambian bajo diferentes condiciones ambientales y como los cambios en las características asociadas a resistencia frente a herbívoros determinan la vulnerabilidad de la planta frente al herbivorismo. Además, destaca la importancia de evaluar los efectos de los cambios ambientales sobre las interacciones entre especies.
[eng]Introduction Herbivory is a key ecological process that regulates the composition and structure of plant communities and determines the energy transferred from primary producers to upper trophic levels. Plants have evolved a suite of defense strategies to avoid or resist herbivory. Tolerance strategies reduce the impact of herbivory in plant fitness (e.g., increased belowground reserves), and resistance strategies reduce preference or performance of the herbivore (e.g., low nutritional quality, high fiber content). These strategies are based on morphological (e.g., toughness) and chemical traits (e.g., phenolic compounds) and can be expressed regardless of the risk of herbivory (constitutively) or in response to herbivore damage (induced). In addition, defense strategies may shift under different environmental scenarios (e.g. higher resource availability often drives a lower investment in resistance). Herbivory in marine systems can be greater than in terrestrial ecosystems, and it can have particularly important consequences when it is exerted upon habitat-forming plants. Seagrasses are key foundation species dominating shallow coastal areas and providing numerous and critical ecosystem services to humans. Given their ecological and socioeconomic relevance, understanding plant-herbivore interactions in these systems is crucial since changes in herbivore populations can result in important disturbances in these ecosystems. The main purpose of this thesis is to understand the effect of changes in environmental factors in plant defense strategies against herbivory and how these changes affect the palatability of the plant, and thus herbivore behavior. Content Nutrient availability stands out for its effects on chemical and morphological plant defense traits. Plants under high nutrient environments in fertilization experiments and regions of higher nutrient availability (i.e. latitudinal comparison) exhibited higher nutritional quality and lower fiber content, both of which can increase their vulnerability to consumption. Interestingly, effects of nutrients on secondary compounds were absent or inconsistent. Simulated herbivory had clear effects on both morphological and chemical plant defense traits, however the two species studied differed in their responses. While in Posidonia oceanica, herbivory induced the production of resistance traits (e.g. fiber, secondary metabolites), in Zostera marina there was no induction of resistance traits, and on the contrary, simulated herbivory reduced their tolerance and resistance. As a result of the changes in traits exhibited by the plants, herbivores preferred the more nutritious repeatedly clipped leaves of Z. marina and the less chemically defended and more nutritious unclipped leaves of P. oceanica. The environmental changes related to global climate change that I analyzed in this thesis (i.e. increased CO2 and temperature), had important effects on defense strategies and susceptibility to grazers of P. oceanica seedlings. The increased pCO2 of seawater enhanced plant photosynthetic activity, leading to higher carbohydrate reserves in the seeds, which are the main storage tissue of the seedling. Although the increase in CO2 decreased leaf nutritional quality (i.e. leaf nitrogen), plants growing under high CO2 were preferred by the herbivores, possibly due to their increase in sucrose content or perhaps other chemical or structural characteristics that were not analyzed. In contrast to CO2, the increase in temperature produced clear negative effects on seedlings; increasing mortality and respiration resulting in greater use of seed reserves. Furthermore, warming reduced leaf fiber, which increased herbivore preference for warmed plants, and thus resulted in a decreased resistance to herbivory. These results illustrate the potential additive or counteractive effects that herbivory could have on determining the effects of environmental changes in seagrass ecosystems. Conclusion The research presented in this thesis contributes to identify the mechanisms that drive the changes in defense strategies against herbivory due to changes in environmental factors. Particularly, how these mechanisms change under different environmental conditions and how changes in traits associated with resistance to herbivores determine the vulnerability of plants to herbivory, highlighting the importance of assessing the effects of environmental factors on species interactions.

Seagrass beds are among the most ecologically important systems in the marine environment. They provide the primary production to nearby coral reef and mangrove communities, and seagrasses comprise a large component of the diets of many marine organisms including fishes, small invertebrate species, and many protected species such as manatees and sea turtles. This consumption provides a pathway for many contaminants to enter the marine food web via the seagrasses. The coastal location of seagrass beds causes them to be especially susceptible to anthropogenic pollution, including accumulation of heavy metals, which has been shown to have many adverse health effects in the seagrasses and marine organisms that feed on them. This study assessed the heavy metal concentrations of seagrasses in three regional locations in South Florida: Port of Miami, Card Sound Aquatic Preserve, and Florida Bay. Three species of seagrasses, Thalassia testudinum, Halodule wrightii, and Syringodium filiforme, which comprise the majority of South Florida seagrass beds, were collected monthly for a period of one year and analyzed for ten heavy metals: (arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), selenium (Se), zinc (Zn)). Concentrations were compared across locations, season, species, and plant part (leaves, shoots, roots, and rhizomes). Concentration ranges, in µg/g (ppm), found in seagrass tissues for all included locations, species, and plant parts were: As (0.02-2.95), Cd (0.09-10.72), Cu (0.38-33.68), Fe (1.52-1877.43), Pb (0.78-156.20), Mn (0.79-300.15), Hg (0.03-16.46), Ni (0.67-87.74), Se (0.01-4.79), Zn (1.48-669.44). Statistical analysis showed significant difference in concentrations among locations, season, species, and plant morphology.

The development of a successful protocol for micropropagating seagrass provides a valuable tool for seagrass-restoration programs and a facility to study their biology (especially their physiology). This work reports on some of the culture requirements of some seagrasses that are commonly found in Western Australia: Posidonia coriacea, P. sinuosa, P. australis and Halophila ovalis. The protocol developed for H. ovalis allows very rapid multiplication and sustainable growth of cultures while the protocol developed for Posidonia requires further development. The culture of Posidonia cariacea proved to be problematic however experimental media that provided insights into its culture conditions. The carbohydrate source was the most important medium component as it affected the development of roots and leaves. The presence of sucrose in the culture media enhanced leaf growth (especially glucose) but decreased the proportion of white roots. More fresh weight, roots, leaves and the proportion of white roots were observed in Posidonia when they were grown in glucose-based media than in mannitol-based media. When mannitol was present in the media, the proportion of white roots was high, which could be attributed to its osmotic effects. Similar responses to sucrose, glucose and mannitol were also observed for P. australis and P. sinuosa. Halophila ovalis was able to grow rapidly on most experimental media. Growth was enhanced by the presence of sucrose in the media and was essential for rapid and sustained growth. Other media components altered the growth of this species, in particular levels of nitrogen (most importantly NH4) influenced root growth and morphology. When H. ovalis is grown in media in moderate or high levels of NH4, root length was significantly reduced and root hair was limited. When NH4 was omitted from the medium, roots were significantly longer and root hairs were prolific. Posidonia coriacea and Halophila ovalis have different growth strategies under natural conditions. H. ovalis is an early succession species that grows rapidly and responds to increased nutrients. P. coriacea is slower growing, colonises later and is Jess responsive to environmental changes than H. ovalis. While the growth responses observed for P. coriacea were significant (in some cases), the differences between means were considerably smaller when compared with H. ovalis. This may be due to the different growth strategies of these species or a lack of fundamental requirement in the conditions under which P. coriacea was grown. Much of what is reported in this thesis for Posidonia will need repeating if the reasons for these differences are identified in the future. In summary, in this thesis I have demonstrated that in vitro propagation of these seagrass species is possible, It is necessary for species-specific protocols to be developed which take into consideration the growth strategies employed by each species. This is particularly significant as many researchers attempt to draw comparisons between species and protocols. The protocols developed in this research increase the knowledge of the biology of these seagrasses and can be incorporated into transplantation protocols in the future.

When we ‘look harder’ to quantify and understand the differences among individuals and populations that produce in variation in resilience within species we achieve better outcomes; successes from medical and agricultural industries are testament to this. Such successes have not yet been achieved for many ecosystems as the variation in resilience within species remains largely unexplored. This knowledge gap is acute for seagrasses which are key determinants of coastal ecosystem structure and function. The overarching goal of this research was to assess the role of environmental variability for influencing the resilience within species of seagrasses and to test these in the context of improving predictions under climate change. Using a combination of field and controlled experiments, this work examined how resilience differs among populations and across life history stages of multiple colonising seagrass species in temperate estuaries of Western Australia. The biological response of Halophila ovalis populations was compared along an estuarine-marine gradient to an extreme rainfall event in a ‘natural’ experiment and to salinity changes in a subsequent controlled experiment. I examined the impacts of abiotic and biotic factors on the response of Ruppia polycarpa over the complete lifecycle in a field manipulative experiment and experimentally tested the effects of salinity on seed dormancy release, germination and seedling establishment. Resilience to hyposalinity varied among H. ovalis populations along the estuarine-marine gradient. Estuarine populations were more resilient to low salinity stress than marine populations consistent with generally being exposed to a more variable salinity regime. In the field, upper-estuary populations recovered to historical baseline conditions whereas lower-estuary populations did not. These differences in recovery were verified by the experimental results which showed that upperestuary populations had greater survival and growth compared to lower-estuary populations. The upper-estuary populations represent an important source of adaptive capacity for the species. These results confirmed that environmental variability associated with the salinity gradient exerts strong selective pressure on seagrass populations and influences their resilience. The response of individual life history stages of R. polycarpa to abiotic and biotic factors varied. Salinity shifts from high to low followed by gradual increases promoted seed germination. Increasing temperature positively impacted seedlings but after a point, caused declines in adults. Swan grazing had minimal impact across life history stages but benefited seedling recruitment. Bet-hedging strategies, including the presence of dormant seeds, were also identified. These results indicated that species persistence results from a combination of environment dependent selection that ‘tailors’ individual life history stages to the conditions they are most likely to be exposed to and strategies that reduce the risk of complete mortality associated with a highly variable habitat. Management of habitats should reflect an understanding of the requirements of each and every life history stage and move away from an emphasis on adults. Overall, the findings of this research indicate that environmental variability and life history stages can generate variation in resilience within seagrass species. This variation matters when predicting the vulnerability of species under climate change. Populations that are naturally exposed to variable conditions are likely to be more resilient to emerging disturbances and reduce the overall vulnerability for the species. In habitats where conditions are highly seasonal, individual life history stages may have greater resilience to disturbances than others and be key modifiers of species’ vulnerability to climate change. These populations and/ or life history stages represent important sources of resilience that may have been underestimated in previous predictions. To move forward, conservation ecologists and managers need to consider the variation in resilience within seagrass and begin testing approaches that leverage this knowledge to reinforce these important species for future climate change.

Thesis (M.S.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Since the Industrial Revolution, coastal pollution has increased and seagrasses, together with other vegetated coastal ecosystems (VCEs), have been identified as potentially important filters and sinks of pollutants, such as CO2 and heavy metals. VCEs can accumulate materials in their soils for millennia reducing their abundance in the surrounding environment. However, VCEs are among the most threatened ecosystems on Earth, putting at risk their ecological services. This dissertation aims to understand the role of VCEs, particularly seagrasses, as environmental archives and biogeochemical sinks. The research assessed: i) the capacity of Posidonia seagrass meadows to sequester metal pollution, through the reconstruction of metal fluxes recorded in seagrass sedimentary archives adjacent to the Port Pirie Pb-Zn smelter in South Australia (SA); and ii) the capacity of VCEs to contribute to climate change mitigation at a regional scale, through a Blue Carbon (BC) assessment for SA. This research showed that seagrass soils in a metal polluted environment can be used to reconstruct the metal contamination history. The seagrass archives at Port Pirie revealed hot-spots of spatial and temporal contamination that reflected the operation of the smelter, its pollution management strategies, wind and currents, and the behaviour of the metals in the marine system. A seagrass area of 110 km 2 has sequestered ~20% of Pb, and ~50% of both Zn and Cd cumulative emissions from the smelter since 1999, highlighting its role in removing metal pollution from the broader environment. Additionally, this work provided insights into the variability of Corg storage among VCEs in SA, an example of an arid region characterized by low productivity. Here the distribution of Corg in the VCEs’ soil reflected both abiotic (e.g. coastal settings, aridity, hydrodynamics) and biotic (habitat type) characteristics of the sampled locations. The mean (±SE) soil Corg stocks and accumulation rates (CAR) in SA for seagrasses, mangroves and tidal marshes were 6.3±0.4, 14±2 and 13±3 kg Corg m -2 and 15±2, 32±7, 30±10 g Corg m -2 -1 yr , respectively. Those estimates are lower than national and global averages, emphasizing the need for region-specific assessments to inform blue carbon (BC) policy and projects. Finally, a seagrass case study showed that while seagrasses are generally very efficient at sequestering Corg, not all sites are suited to demonstrating this. At False Bay, a lack of net sediment accumulation and hydrodynamic-driven mixing prevented the application of radionuclide methods to determine CAR, thereby preventing to demonstrate ‘additionality’ using this method. This finding highlighted the importance of selecting suitable sites and methods for seagrass BC projects. The findings demonstrate the important role that seagrasses play as biogeochemical sinks, in this case for metal pollution and atmospheric CO2, but potentially for a wide range of materials. The ability of seagrasses to sequester these materials over millennia also makes them useful as archives, revealing past environmental conditions including pollution histories. These features make seagrasses potentially useful management tools, to aid in the monitoring of coastal ecosystems and to understand past trajectories which can inform current and future management. The research also highlights the need to conserve VCEs to maintain their valuable role as biogeochemical sinks and to prevent the release of stored materials into the broader environment.

The seagrass Zostera japonica Aschers. and Graebn. occurs as pure populations and in mixture with Zostera marina L. along the intertidal regions of southwest British Columbia. At the Roberts Bank study area seed and seedling dynamics were studied in three vegetation zones: a landward monospecific zone of Z. japonica, a zone of co-existing Z. japonica and Z. marina, and a seaward monospecific zone of Z. marina. Many more seeds were produced than were found in the sediment, and even fewer germinated. Zostera japonica seeds were most abundant in the seed bank in the upper zones where there is high Z. japonica density. Even though seeds remained in the water column for up to two months, very few seeds dispersed into the lower zone populated by Z. marina. thus limiting Z. japonica's colonization of the lower zones. It is unclear what limits the dispersal of Z. japonica seeds. Of the seeds that were incorporated into the sediment few germinated (5% or less). When seeds were planted in buckets placed into the sediment, with and without Z. marina, Z. japonica was able to germinate, grow, and reproduce in one year throughout the study area. Seedlings that emerged earliest (in April) either did not establish or did not survive as long as those seedlings that emerged later in May and June. Seedlings were often found uprooted, floating in the water. The rim of the buckets and the presence of Z. marina shoots appeared to protect the Z. japonica seedlings, preventing uprooting, but the results were not conclusive. Once seedlings became established, they spread vegetatively at a rapid rate and can persist throughout the winter, either as reduced shoots or as overwintering rhizomes. These overwintering plants contribute greatly to the following year's population.
Science, Faculty of
Botany, Department of
Graduate

Seagrass meadows in south-western Australia exist along a gradient of hydrodynamic disturbance and may be subjected to varying degrees of sediment movement leading to burial and erosion. Such disturbance may play a role in structuring seagrass assemblages and has contributed to the failure of some attempts at seagrass restoration in the region. The seagrasses in south-western Australia occur in a microtidal environment dominated by swell waves, locally generated wind waves and oscillatory currents. This poses challenges not experienced or studied in environments of the northern hemisphere where most other seagrass rehabilitation has taken place, which are dominated by unidirectional tidal currents. This thesis examined the relationship between seagrass assemblages and hydrodynamic disturbance, along with seagrass growth responses to changes in sediment height and the role of shoot density in determining grain size characteristics in natural and transplanted seagrass meadows. The distribution of seagrass assemblages in Owen Anchorage was examined in relation to hydrodynamic disturbance, approximated by the calculation of a Relative Exposure Index (REI), variants of which considered effective fetch, depth and the long term wind record. Of the variants examined, REI including the full wind record best differentiated between seagrass assemblages and the significant differences between assemblages support the notion that hydrodynamic processes play a role in structuring seagrass distribution in the study area. Short term changes in sediment height were monitored at six sites using electronic sediment height loggers during summer and winter. Highest levels of sediment movement occurred in winter and were associated with westerly winds. Summer observations showed lower levels of sediment movement, with no particular wind characteristics associated with changes in height. Wind direction and uninterrupted fetch were more important than wind speed when determining the level of sediment movement in the study area. In order to assess the extent to which transplanted Posidonia australis tolerates burial and erosion, transplanted sprigs were subjected to experimental changes in sediment height (-2, 0, 4, 8 & 16 cm) between November 2007 and April 2008 in the relatively sheltered Southern Flats area of Cockburn Sound. Transplants exhibited high survival rates (> 90%) in all treatments except the 16 cm burial treatment, which experienced total mortality. Active rhizome extension was observed in all treatments, along with the production of new shoots, except in the highest burial treatment. There was little evidence of an increase in vertical growth or the production of vertical shoots. This study indicated that P. australis transplants are tolerant to changes in sediment height between -2 and 8 cm, however a critical threshold exists between 8 and 16 cm, above which transplant mortality is high. As such, consideration of the scale of sediment movement will play an important role in site selection for seagrass restoration projects using this species. The role of seagrass shoot density in influencing changes in sediment height and grain size characteristics was examined in both transplanted and natural Posidonia australis meadows over the course of one year. Transplanted seagrass patches at spacings of 1.0, 0.5, 0.25 and 0.125 m were established, along with natural meadows adjusted to 100, 75, 50, 25 and 0% of their initial shoot density, with all sites situated in the relatively sheltered Southern Flats region of Cockburn Sound. Short term changes in sediment height were similar between all transplanted and natural seagrass patches, with features such as sand ripples associated with the south-westerly sea breeze observed. Long term monitoring indicated that higher shoot densities experienced greater accretion than lower ones. Within the density manipulated natural meadows, higher shoot densities coincided with a relatively higher proportion of fine sediments (250 µm, 125 µm and <63 µm). Sediments within the transplanted patches became increasingly fine over the course of the experiment, with higher densities showing the greatest proportion of fine sediment, although sediments within all transplant patches were significantly coarser than natural meadows. As such, grain size characteristics of the transplants represented an intermediate condition between natural meadows and unvegetated sediments. These results show that seagrass shoot density plays a role in structuring the sedimentary environment within seagrass meadows. These findings can be applied to aid in the future planning and execution of seagrass restoration techniques using Posidonia australis in the Perth metropolitan region. In particular, sites can be assessed for suitability in terms of exposure and sediment movement prior to undertaking restoration. This may enhance the success of restoration activities by ensuring that optimal sites are selected.

The present study is one of the first attempts to analyze the societal importance of seagrasses (marine flowering plants) from a Natural Resource Management perspective, using a social-ecological systems (SES) approach. The interdisciplinary study takes place in East Africa (Western Indian Ocean, WIO) and includes in-depth studies in Chwaka Bay, Zanzibar, Tanzania. Natural and social sciences methods were used. The results are presented in six articles, showing that seagrass ecosystems are rich in seagrass species (13) and form an important part of the SES within the tropical seascape of the WIO. Seagrasses provide livelihoods opportunities and basic animal protein, in from of seagrass associated fish e.g. Siganidae and Scaridae. Research, management and education initiatives are, however, nearly non-existent. In Chwaka Bay, the goods and ecosystem services associated with the meadows and also appreciated by locals were fishing and collection grounds as well as substrate for seaweed cultivation. Seagrasses are used as medicines and fertilizers and associated with different beliefs and values. Dema (basket trap) fishery showed clear links to seagrass beds and provided the highest gross income per capita of all economic activities. All showing that the meadows provide social-ecological resilience. Drag-net fishery seems to damage the meadows. Two ecological studies show that artisanal seaweed farming of red algae, mainly done by women and pictured as sustainable in the WIO, has a thinning effect on seagrass beds, reduces associated macrofauna, affects sediments, changes fish catch composition and reduces diversity. Furthermore, it has a negative effect on i.a. women’s health. The two last papers are institutional analyses of the human-seagrass relationship. A broad approach was used to analyze regulative, normative and cultural-cognitive institutions. Cooperation and conflict take place between different institutions, interacting with their slow or fast moving characteristics, and are thus fundamental in directing the system into sustainable/unsustainable paths. Ecological knowledge was heterogeneous and situated. Due to the abundance of resources and high internal control, the SES seems to be entangled in a rigidity trap with the risk of falling into a poverty trap. Regulations were found insufficient to understand SES dynamics. “Well” designed organizational structures for management were found insufficient for “good” institutional performance. The dynamics between individuals embedded in different social and cultural structures showed to be crucial. Bwana Dikos, monitoring officials, placed in villages or landing sites in Zanzibar experienced four dilemmas – kinship, loyalty, poverty and control – which decrease efficiency and affect resilience. Mismatches between institutions themselves, and between institutions and cognitive capacities were identified. Some important practical implications are the need to include seagrass meadows in management and educational plans, addressing a seascape perspective, livelihood diversification, subsistence value, impacts, social-ecological resilience, and a broad institutional approach.

Seagrasses are marine foundation species that form ecologically important habitats in coastal areas around the world. They provide a range of ecosystem services, including coastal protection and the recently recognised large contribution to global carbon sequestration and storage. To date, the majority of published studies on the aforementioned ecosystem services is limited to specific geographic regions and seagrass species. This PhD study attempted to explore and provide the first evidence, to the best of our knowledge, on the role of Scottishseagrasses as carbon sinks and sediment stabilisers. In 2013, shoot dynamics of Zostera noltii plots were monitored biweekly and seasonally in the Forth estuary and digital images of the surveyed plots were taken for the development of a remote sensing technique which would accurately estimate the vegetation cover. In 2014, sediment samples from vegetated and unvegetated plots within beds of Z. marina and Z. noltii were collected from all the major estuaries along the east coast of Scotland, from the Firth of Forth in the south to Dornoch Firth in the north. Samples were analysed for organic matter, organic carbon, radionuclides 210Pb, 137Cs and 241Am, and δ13C in order to determine the organic matter and organic carbon density, longevity and sources of carbon respectively. To explore the role of seagrass in sediment deposition and stability, surface elevation was measured monthly in seagrass plots and bare sediment in the Forth estuary over two years. The results and main mechanisms underlying these findings are reported and discussed in detail in each chapter. In short, the proposed method based on digital images provided estimates of seagrass coverage that are more accurate than observers' estimates, with some constraints when macroalge and/or extreme light are present. Intertidal seagrass meadows in Scotland showed significantly enhanced carbon storage compared with bare sediment. Seagrass plots contained variable quantities of carbon in their sediments with species composition having a significant effect on carbon stocks, whereas depth and seagrass abundance had no effect on carbon stores. Despite their small above-ground biomass Scottish seagrass plots had a strong influence on sediment deposition and prevented erosion. Further research is needed to understand what factors drive large carbon sequestration and storage at some sites, thus contributing policy-relevant information on the prediction of the seagrass carbon hot-spots. Also, long-term datasets on surface elevation change are important in order to understand the effect of all the processes involved on sediment deposition in seagrass beds.

Seagrass beds of Zostera capricorni are an integral part of the estuarine landscape along the east coast of Australia forming important habitats for juvenile fish and macroinvertebrates. Seagrass beds can vary in their spatial structural such as their size, shape and patchiness of seagrass cover. They can also be located within the estuarine landscape context such as their proximity to other habitats or their location within the estuary. The influence or correlation of these landscape or seascape spatial features of seagrass beds on the assemblages of seagrass fauna (fish and macroinvertebrates) was tested in this thesis. It was found that the spatial structure of seagrass beds (size and shape), their patchiness of the seagrass cover and location within the estuary (close or far from estuary mouth) were correlated with the assemblages of fish within seagrass beds. In particular it was demonstrated that there were greater densities of small fish species in the small compared to the large beds of Z. capricorni. This occurred regardless of the placement of the seagrass bed within the estuary context, its proximity to other habitats or patchiness of cover. Further experimentation using artificial seagrass patches demonstrated that this effect of patch size was independent of the perimeter length or perimeter to area ratio of the seagrass beds. It was hypothesised that the greater density of small fish species in small seagrass beds could be attributed to the greater proportion of edge habitats in small beds i.e. edge-mediated effects. However, the number of fish species per net haul in edges and inner regions of small and large seagrass beds were measured and found not to be different. The outcomes of this research suggest that to conserve the small fish species within an estuary, it is essential to protect even the small and patchy seagrass beds. A network of seagrass beds from all regions of the estuary is also required and the adjacent mangrove forests must be included
Doctor of Philosophy (PhD)

[Truncated abstract] Biogeochemical processes in seagrass sediments influence growth and nutrition of seagrasses. This thesis investigates the below-ground interactions between biotic and abiotic factors that influence seagrass nutrition and growth, with focus on a small species of seagrass, Halophila ovalis (R. Br.) Hook ƒ., from the Swan River Estuary, Western Australia. Seagrass showed significantly lower growth and an increase in leaf nitrogen and phosphorus concentrations with increased organic matter loading. With maximal light reduction, lower growth rates and average leaf weights were observed, and leaf nitrogen and phosphorus concentrations were higher. Light reduction was also shown to increase bioavailability of inorganic nutrients within porewater of seagrass sediment . . . Sulphide was hypothesised to have an inhibitory effect on nutrient uptake of Halophila ovalis. Below-ground sulphide inhibits the photosynthetic efficiency of photosystem II at sulphide concentrations greater than 1 mM. Sulphide exposure enhanced phosphate uptake, with no significant effect on ammonium uptake of H. ovalis. This thesis demonstrates that biogeochemical processes both constrain the potential growth of seagrasses and influence the nutrient status of seagrass tissue. Consideration of the influence of sulphide stress on seagrasses is likely to be particularly important for anthropogenically influenced aquatic systems, where inputs of organic matter are enriched relative to pristine ecosystems. A better understanding of biogeochemical processes will allow researchers to predict how future changes in sediment chemistry will influence seagrass meadows.

The two seagrasses Zostera marina L. and Zostera japonica Aschers. and Graebn. coexist in an intertidal region of the south-west coast of British Columbia. At the Roberts Bank study area three vegetation zones were identified; a seaward monospecific zone of Z. marina cover, a zone of mixed Z. marina and Z. japonica, and a landward monospecific zone of Z. japonica. The study investigating possible interactions between the two species was undertaken in three parts. First, a descriptive component compared numerous morphological characters, phenological data, and the population dynamics for each species between monospecific and mixed populations using univariate and multivariate statistical techniques. For both species shoots in deeper intertidal waters tended to be longer and with greater biomass than shoots from shallower intertidal areas. The most pronounced difference was the suppression of lateral shoot development of Z. japonica under a Z. marina canopy. Second, transplants of monospecific adult patches indicated that vigorous lateral branching would proceed regardless of location on the intertidal gradient and confirmed that the suppression of Z. japonica growth was due to competition. Third, a manipulation experiment using artificial shoots to mimic shading under a Z. marina canopy did not directly indicate that the attenuation of light under a Z. marina canopy was the mechanism for suppression of Z. japonica population growth. The artificial shoots did not adequately mimic Z. marina shoots as a shading canopy. In addition the "patch" design of the manipulation experiment enhanced lateral branching while reducing shoot length. The results of the manipulation experiment were therefore considered in conjunction with the results of the descriptive study and the transplant experiments.
Science, Faculty of
Botany, Department of
Graduate

Seagrass meadows provide crucial ecosystem services to the coastal zone but globally are threatened. Seagrass loss to date has mainly been attributed to anthropogenic activities that reduce light quantity, such as dredging, declining water quality from urban and agricultural run-off and eutrophication. However, light quality (wavelengths of light) is also altered by these anthropogenic stressors as well as natural events. This study consisted of three main components: (1) characterising light quality to which seagrasses are exposed across a local natural estuarine-ocean gradient and with a human impact pressure; (2) the influence of monochromatic light quality (blue λ=451 nm; green λ=522 nm; yellow λ=596 nm and red λ=673 nm wavelengths and full-spectrum light λ=400 – 700 nm, at 200 μmol photons m-2 s-1) on Halophila ovalis and Posidonia australis at different life-history stages; and (3) the effects of light quality and quantity representative of a commercial dredging operation (15 mg L-1 TSS, 50 and 200 μmol photons m-2 s-1) on H. ovalis adult plants. The field work demonstrated that the quality of light to which seagrasses are exposed varies along a natural gradient but the nature of the shift is also dependent on time of year. Additionally, human impact such as dredging can expose seagrasses to spectra outside of the natural range detected in this study, and the magnitude of this shift is dependent on depth and TSS concentrations. Results from the monochromatic light quality experiments demonstrated, for the first time, the seagrass responses to light quality across several plant scales as well as different life-history stages. Halophila ovalis and P. australis showed different responses, likely due to their respective growth strategies. Adult H. ovalis (a colonising species) plants were negatively impacted by monochromatic blue, green and yellow light treatments, while seeds and seedlings performed better under red and full-spectrum light. Conversely, P. australis (a persistent species) adults showed no significant responses to any of the monochromatic light quality treatments, while seedlings demonstrated a physiological acclimation to blue light. The simulated dredging spectrum experiment demonstrated a significant impact of reduced light quantity on H. ovalis photo-physiology and growth, but the only significant effect of light quality was on the concentration of the pigment antheraxanthin. The lack of effect of light quality on growth indicates that: a) while seagrass are sensitive to changes in light quality, not all shifts induce negative biomass responses; b) the effects of altered light quality are less severe when a mixture of wavelengths are present; and c) in this species, reduced light quantity was more important than changes in light quality. Therefore, when considering the practical management of seagrasses in relation to short-term dredging activities, using light quantity thresholds is sufficient for management triggers. Overall, while there were some (positive and negative) responses to blue, green, yellow and red light, lethal effects were not detected for either the colonising or persistent species, suggesting that seagrasses have the VI capacity to acclimate to and/or tolerate extreme changes in light quality and maintain short-term growth at sufficiently high irradiances. However, sub-lethal responses were determined which may affect the ability of seagrasses to maintain resilience against other stressors. Therefore, environmental conditions that alter light quality have the potential to indirectly influence the overall resilience seagrasses.

Seagrass restoration programmes are becoming increasingly important in helping to maintain the biodiversity of coastal systems in many parts of the world, due to large areas of seagrass being lost over the last 50 years. The success of any restoration programme should ultimately be based on transplanted seagrass meadows acting in a similur ecological manner as the meadows they are replacing. However, success has generally been measured by examining survivorship and increases in physical structure of transplanted meadows. Few programmes have incorporated other ecological functions in establishing goals and objectives. The purpose of this research was to determine how ecological functions establish in transplanted Posidonia australis meadows of Oyster Harbour, Western Australia, and to determine how transplanting factors (e.g. planting density, patch size and patch shape) may influence these processes. The study has also determined whether monitoring the return of structural variables of seagrass represents the establishment of ecological functions, or whether monitoring ecological functions is required in determining the overall success of a restoration programme.

The European Water Framework Directive (WFD) has encouraged considerable research on the development of water quality bioindicators. Seagrasses, that are highly sensitive to direct and indirect anthropogenic stress, and specified as quality elements from the WFD, have been at the center of this effort. In this study the use of Cymodocea nodosa, a widely distributed angiosperm in the Mediterranean Sea, as a bioindicator of anthropogenic stress was tested. Key biotic features of two meadows growing in locations of contrasting ecological status in the N. Aegean Sea, Greece, were sampled and analysed following a hierarchical designed approach. Plants from the degraded meadow (Nea Karvali) were found to have significantly (p<0.05) longer leaves, higher N and P (%) content and lower C/N ratio in their leaves than the less degraded-pristine (Brasidas and/or Thasos) meadows. The application of chlorophyll fluorescence as an easily measurable indicator of the anthropogenic stress has been tested before with limited success. This study, based on a large amount of measurements (ca.500 per meadow) carried out after a short acclimation period in the laboratory under constant temperature and irradiance conditions, showed significantly higher (p<0.05) ΔF/Fm’ and Fm values at plants from the degraded than from the pristine meadows. Three sets of laboratory 8-days experiments were carried out under optimal growth temperature (21±1.5oC) in order to investigate cause-effects relationships between the main local stressors (nutrients-N, P, irradiance and heavy metal-Cu) to shoots collected from differently impacted meadows. High nutrient concentrations (30μΜ Ν-ΝΟ3; 2μM P-PO4) had a significant effect (p<0.05) on ΔF/Fm’ only on shoots from the pristine site. Low irradiance (37 μmol photons m-2 s-1) resulted in a significant increase (p<0.05) of ΔF/Fm’, while high copper concentrations (>4.7 μM) had the opposite effect. Through these experiments light availability and nutrients were identified as the main factor that affects the meadows health.

An intensive study was conducted on Posidonia australis (Brown) Hook f in south east Australia. Three sites were studied intensively (16 times a year for two years) these being in Quibray Bay (sites 1 & 2) and Port Hacking (Site 3). Site 4 in Jervis Bay and site 5 at Bonna Point in Quibray Bay were studied less intensively (four times a year for two and one year respectively). Variables examined included shoot density, leafing rate, leaf number, unit leaf weight, leaf biomass per shoot as well as biomass production of leaf, sheath, rhizome, root and reprod'u'ctive structures. Correlations between seasonal variations in these parameters were established with water temperature, light intensity and rainfall. A procedure was developed and employed which estimated net leaf production without causing major damage to the study populations. This procedure also allowed estimation of several leaf production variables for the first time. The effects of stress and disturbance on meristem activity were examined. The correlation between leaf production and standing stock was established and the suitability of using seasonal changes in leaf standing stock or biomass values to estimate production seasonality was examined. The applicability to P. australis of two procedures that indirectly estimate the plastochron was also investigated. Among the P. australis studied, significant seasonal variation occurred in unit leaf weight (mg * cm'l), total leaf biomass, leaf and rhizome biomass production, plastochron interval, and leaf and non-leaf production. The rates of most production variables peaked in late spring with minimal values recorded in early to mid-winter. Seasonal changes in relative leaf growth rate, leaf and rhizome production of P. australis shoots, highly correlated with changes in water temperature and light intensity. Mean total shoot biomass production ranged from 2.33 to 4.74 g * m'2 * day".

The intensification of seawater warming and the co-occurrence of different anthropogenic stressors are threatening coastal marine habitats, including seagrasses which form a unique group of marine plants supporting diverse and productive ecosystems. However, seagrasses are declining globally and are one of the most threatened ecosystems on earth. The simultaneous presence of sea warming with local pressures can result in antagonistic, additive, or synergic effects depending on their interactions. One of the main concerns of rapid environmental shifts is that these changes do not allow species to react swiftly enough in order to cope with and survive in the new more stressful environment. Thus, the analysis of the degree of phenotypic plasticity could reveal important insights into seagrasses' persistence. The main aim of this doctoral research was to investigate the resilience capacity of Posidonia oceanica, endemic of the Mediterranean Sea, to environmental changes. Plants’ performances were analyzed exploring the effect of local environmental conditions in driving different plants' responses to single and multiple stresses. To this end, I previously reviewed the concept of phenotypic plasticity suggesting mesocosm experiments and reciprocal transplants as useful approaches to assess the phenotypic plasticity that allows discriminating the effect of local adaptation and acclimation in plants’ responses to common stress conditions. Starting from these considerations, I performed a mesocosm experiment where plants growing in oligotrophic (Ol plants) and eutrophic (Eu plants) environments were exposed to single (nutrients and temperature increases) and multiple stresses (nutrients combined with temperature increases). Plants’ performance was assessed applying an ‘omic approach’, exploring physiological and transcriptional responses with the focus on the dynamics of DNA methylation during the exposure to stress conditions. Physiological analysis revealed that the exposure to nutrients induced the worst effect in the leaf in both Ol and Eu plants while antagonistic effects with temperature were found in Eu plants for some parameters. Accordingly, the analysis of the whole battery of transcribed genes revealed an organ-specific response depending on the plants’ origin and stress exposure. I also aimed to investigate the dynamics of DNA methylation selecting key genes and analyzing the global DNA methylation levels during the exposure to stresses in both Ol and Eu plants. DNA methylation levels changes according to the plants’ origin and environmental stresses, demonstrating that DNA methylation changes dynamically with the surrounding environmental conditions contributing to the regulation of stress responses in P. oceanica plants. In the framework of designing appropriate restoration strategies, approaches to assisted evolution can be implemented. In this thesis, I applied the thermo-priming treatment to P. oceanica seedlings through exposure to a simulated warming event. This priming process modifies the phenotypic state of an organism favouring phenotypic-plastic adjustments to future environmental stress conditions. Primed seedlings performed better during the re-occurring stress event than un-primed ones. This possibility provides important implications for restoration and conservation management. During the Ph.D. thesis, I also authored a review paper, highlighting the importance of the genetic component in seagrass restoration, where the hypotheses and the knowledge acquired during the study, were integrated for providing a conceptual framework to serve future restoration plans. The integration of studies related to local adaptation and acclimation, local environmental disturbances with the analysis of the genetic and epigenetic component, should always be considered to select the most appropriate donor site to restore degraded habitats, guaranteeing the success of the restoration plan.
The intensification of seawater warming and the co-occurrence of different anthropogenic stressors are threatening coastal marine habitats, including seagrasses which form a unique group of marine plants supporting diverse and productive ecosystems. However, seagrasses are declining globally and are one of the most threatened ecosystems on earth. The simultaneous presence of sea warming with local pressures can result in antagonistic, additive, or synergic effects depending on their interactions. One of the main concerns of rapid environmental shifts is that these changes do not allow species to react swiftly enough in order to cope with and survive in the new more stressful environment. Thus, the analysis of the degree of phenotypic plasticity could reveal important insights into seagrasses' persistence. The main aim of this doctoral research was to investigate the resilience capacity of Posidonia oceanica, endemic of the Mediterranean Sea, to environmental changes. Plants’ performances were analyzed exploring the effect of local environmental conditions in driving different plants' responses to single and multiple stresses. To this end, I previously reviewed the concept of phenotypic plasticity suggesting mesocosm experiments and reciprocal transplants as useful approaches to assess the phenotypic plasticity that allows discriminating the effect of local adaptation and acclimation in plants’ responses to common stress conditions. Starting from these considerations, I performed a mesocosm experiment where plants growing in oligotrophic (Ol plants) and eutrophic (Eu plants) environments were exposed to single (nutrients and temperature increases) and multiple stresses (nutrients combined with temperature increases). Plants’ performance was assessed applying an ‘omic approach’, exploring physiological and transcriptional responses with the focus on the dynamics of DNA methylation during the exposure to stress conditions. Physiological analysis revealed that the exposure to nutrients induced the worst effect in the leaf in both Ol and Eu plants while antagonistic effects with temperature were found in Eu plants for some parameters. Accordingly, the analysis of the whole battery of transcribed genes revealed an organ-specific response depending on the plants’ origin and stress exposure. I also aimed to investigate the dynamics of DNA methylation selecting key genes and analyzing the global DNA methylation levels during the exposure to stresses in both Ol and Eu plants. DNA methylation levels changes according to the plants’ origin and environmental stresses, demonstrating that DNA methylation changes dynamically with the surrounding environmental conditions contributing to the regulation of stress responses in P. oceanica plants. In the framework of designing appropriate restoration strategies, approaches to assisted evolution can be implemented. In this thesis, I applied the thermo-priming treatment to P. oceanica seedlings through exposure to a simulated warming event. This priming process modifies the phenotypic state of an organism favouring phenotypic-plastic adjustments to future environmental stress conditions. Primed seedlings performed better during the re-occurring stress event than un-primed ones. This possibility provides important implications for restoration and conservation management. During the Ph.D. thesis, I also authored a review paper, highlighting the importance of the genetic component in seagrass restoration, where the hypotheses and the knowledge acquired during the study, were integrated for providing a conceptual framework to serve future restoration plans. The integration of studies related to local adaptation and acclimation, local environmental disturbances with the analysis of the genetic and epigenetic component, should always be considered to select the most appropriate donor site to restore degraded habitats, guaranteeing the success of the restoration plan.

The unrelenting threat of seagrass loss resulting from reduced light availability has motivated this characterisation of responses of Posidonia sinuosa Cambridge et Kuo to light availability and their application as monitoring tools. The study comprised of three major components: an assessment of P. sinuosa characteristics across a depthrelated gradient in long-term light availability; an in situ experiment to test for responses to short-term light reduction; and experimental investigations into the role of translocation to cope with reduced light availability. Across depth-related gradients of light, in two locations, near Perth in Western Australia, the minimum light requirement (MLR) of P. sinuosa at the depth limit was 8.5% of sub-surface irradiance. Shoot density and biomass consistently differed across the gradient while other morphological and growth differences between depths were inconsistent between location and season or did not follow the gradient of light reduction. Physiological characteristics including RLC-derived characteristics, light harvesting and photoprotective pigments and nutrient and carbohydrate concentration demonstrated few depth-related differences but showed limited adjustment between seasons. The light dependency of these observations was validated experimentally by in situ shading at a shallow (3- 4 m) and deep (7- 8 m) site with light (LS; 87% of ambient light), moderate (MS; 27%) and heavy shading (HS; 9% at shallow only). After 106 d, significant shoot loss had occurred but complete loss did not occur after 206 d. Shoot loss substantially reduced the light attenuation coefficient of the canopy (and self-shading) from 2.8 (control) to 0.5 m-1 (HS). Carbohydrate reduction occurred in most shade treatments probably supporting respiration and growth (which was not affected by shading except in MS at the deep site). Few other responses were observed in treatments near or above MLR, but in those below MLR (HS at the shallow and MS at the deep site) photosynthetic and morphological responses were detected including photosynthetic characteristics, length/weight ratio of leaf growth and δ13Cvalues. Following removal of shading, recovery of shoot density was slow, remaining significantly lower than the control after 384 d, and depended on shoot density; rate of shoot production was faster when higher shoot densities remained following shading. Nutrient translocation of 15N and 13C within and between shoots was investigated in the early phase of imposed shading. Following incubation of a mature leaf (ML), the 13C and 15N accumulated in the young growing leaf(YL) and rhizome, with up 32% and 44% of the 15N and 13C, respectively, appearing in the YL after 29 d. Resorption of structural nitrogen (N) from the ML may also contribute to YL N requirements but not for carbon (C). For 13C and 15N exported from the shoot, there was a trend for greater 13C accumulation away from, rather than towards, the rhizome apex but not for 15N. Most of the C and N was recovered in the rhizome, and not shoots, after 8 and 15 d. There was no evidence that the translocation of C or N within or between shoots is altered as an early response to shading. For P. sinuosa, shoot density reductions dominate the response to reduced light availability at light intensities above MLR and can be considered a meadow-scale response with benefits for reduced self-shading. Growth rate of shoots is usually unaffected by depth (during summer) or shading. Below MLR, other morphological and physiological responses can also occur. Clonal integration via the rhizome is important for carbohydrate storage and remobilisation during periods of low light, but changes to translocation between or within shoots are not important shade responses. These findings should also be relevant to other meadow-forming and persistent seagrass species. Shoot density was recommended as an appropriate monitoring indicator because it is consistently responsive and crucial in P. sinuosa's response mechanisms, while other physiological responses including carbohydrates in the rhizome have potential as monitoring tools.

Lake Illawarra is a shallow barrier lagoon, located on the south-eastern coast of Australia. Eutrophication, referring to the enrichment of water by inorganic plant nutrients (primarily nitrogen and phosphorus), is one of the key environmental problems in Lake Illawarra. Management of macroalgae in Lake Illawarra is a major issue; excessive blooms of macroalgae, resulting in odours, access problems and community concern over Lake health, have led to many management strategies, including direct harvesting of algal biomass. Little information is available on the factors responsible for excessive growth of macroalgae in Lake Illawarra, although over supply of nutrients has often been cited as the primary cause. The aim of this study was to investigate the distribution, diversity, biomass and nutrient relationships of seagrasses and macroalgae in Lake Illawarra, and to determine what contribution, if any, macrophytes make to the Lake’s nutrient budget. Firstly, detailed species lists and taxonomic descriptions were prepared for macrophytes occurring in Lake Illawarra, between June 2000 and July 2003. This study focused primarily on shallow (< 1 m depth), inshore areas of Lake Illawarra, where problematic macroalgal blooms frequently occur. Seagrasses found in Lake Illawarra are Zostera capricorni, Ruppia megacarpa, Halophila ovalis and Halophila decipiens. In addition, 35 species of macroalgae were recorded and described; these included: 14 species from 7 genera of green macroalgae; 9 species from 9 different genera of brown macroalgae; and, 8 species from 8 genera of red macroalgae. The biomass of seagrasses and macroalgae in Lake Illawarra were documented seasonally (winter and summer) at four key Lake Illawarra sites; these included two R. megacarpa sites and two Z. capricorni sites. Average R. megacarpa and Z. capricorni dry weight (DW) biomasses (above and below-ground material) ranged from 54.8 - 440 g DW m 2 and 58.1 - 230 g DW m 2, respectively. Significant die-back, particularly of Z. capricorni, occurred in winter; summer biomasses were up to 1.5 - 3.9 times higher than winter biomasses. Below-ground material (roots and rhizomes) comprised 20 - 45 % and 40 - 67 % of total plant biomass for R. megacarpa and Z. capricorni, respectively. Macroalgal biomass in 2000-03 was notably lower than in previous decades; this may be due to drought, as well as improvements in water quality. Maximum biomasses of macroalgae recorded in the present study were 150 - 370 g DW m 2. Algal blooms were composed primarily of the filamentous chlorophytes, Chaetomorpha linum and Chaetomorpha billardierii. The highest seagrass (R. megacarpa) and macroalgal biomasses usually occurred at the Oasis Caravan Park site, located along the eastern Lake Illawarra peninsula. Tissue nutrient analyses were conducted on the most abundant seagrasses (Z. capricorni and R. megacarpa) and macroalgae occurring at four sites in Lake Illawarra, between spring 2000 and winter 2002. Total C contents of macrophytes varied from 23.3 - 42.0 % C for seagrasses, and 28.0 - 39.7 % C for macroalgae. The δ13C and δ15N contents of seagrasses ranged from -7.7 to 15.9 ‰ and 0.7 - 9.0 ‰, respectively. The most significant seasonal variations in seagrass δ13C contents and, to a lesser extentδ15N contents, occurred in Z. capricorni located at the source of fresh water input, Mullet Creek. Macroalgae showed a greater variation in isotopic signatures than the seagrasses, ranging from 4.9 to 19.8 ‰ (δ13C) and 1.8 - 14.6 ‰ (δ15N). Differences between species at the same site were often more significant than differences between the same species at different sites. Seagrass leaf N and P contents ranged from 1.74 - 4.13 % (mean ± s.e.: 2.62 ± 0.05 % N) and 0.12 - 0.59 % P (mean ± s.e.: 0.31 ± 0.01 % P); leaf N and P contents were typically double those of roots/rhizomes. N contents varied between species and sites, but P contents of Z. capricorni were usually significantly higher than R. megacarpa. Z. capricorni C and N contents increased in winter, corresponding to lower winter biomasses. Seagrass leaf biomass and tissue P contents peaked in summer 2002, which may be related to higher water column P concentrations in summer. Tissue N and P contents of macroalgae were more variable than those of the seagrasses, and ranged from 0.85 - 3.95 % N and 0.03 - 0.58 % P. The average C/P (808 ± 65) and N/P (47.9 ± 3.47) molar ratios of macroalgae were typically double those of the seagrasses. Low concentrations of tissue P, with respect to N, in R. megacarpa and macroalgae implied P limitation on several occasions, particularly when macrophyte biomasses were low. High tissue N contents in Lake Illawarra macrophytes suggested N limitation of biomass formation rarely occurred. Evidence of P, rather than N, limitation in macrophytes is surprising considering most data suggests N limitation of phytoplankton production in Lake Illawarra. The estimated pools of N and P contained in Lake Illawarra macrophyte biomass were similar to those present in the water column, but appeared minute when compared to the N and P stored within Lake Illawarra sediment. Laboratory culture experiments were conducted to evaluate the response of the most problematic alga, Chaetomorpha linum, to nutrient enrichment. Water temperatures of 20 - 25°C were found to promote the highest growth rates (up to 27 % WW d 1) of C. linum, but high growth rates (13 % WW d 1) were also recorded at 10°C, the lowest winter water temperature recorded in Lake Illawarra. Enrichment with N, rather than P, had the greatest effect on C. linum; growth rates were significantly reduced in treatments without added N, but treatments with N-alone were statistically similar to N+P treatments. It was concluded that in Lake Illawarra, C. linum was strongly nitrogen limited. The ability of C. linum to grow successfully in culture, under a range of nutrient treatments, and without added phosphorus, in particular, correlates with the excessive growth of this alga in Lake Illawarra. This study has made a significant contribution to the understanding of seagrass and macroalgal growth, biomass and distribution in Lake Illawarra. This information will assist with the long-term management of macroalgal problems in Lake Illawarra.

The temporal spectral light environment of shallow areas of the lower Chesapeake Bay was characterized by cosine collection of downwelling diffuse irradiance at 12 wavelengths between 400 and 700 nm. An extensive monthly and site comparison of spectral attenuation coefficients is presented and compared with previous measurements of the light quality environment of the Chesapeake Bay and other estuaries and marine waters. Spectral irradiance and attenuation of light in a mangrove creek and Thalassia testudinum bed of Laguna de Terminos, Campeche, Mexico and their relationships to wind-driven suspension of particulate matter, and dissolved substances from the mangrove swamp is also discussed. A review of the physics of spectral attenuation in estuaries is included. Particular attention was given to the relationship between the occurrence of seagrasses (Zostera marina mainly) in the Chesapeake Bay and spectral attenuation. Potential losses of photosynthetically storable radiation (PSR) due to reduced light quality in non-vegetated areas is calculated. A theoretical homeostatic relationship between seagrass leaf baffling of the water column, light quality and critical bed size is presented. The logic and output of a digital ecosystem simulation model of theoretical estuarine photosystem responses to simulated varying underwater light quality is presented. The model assumes that photosystems adapt to maximize power. Conclusions include: a dramatic pattern of seasonal spectral attenuation in the lower Chesapeake Bay; seasonal differences in spectral attenuation between vegetated and unvegetated sites; 63% less violet light was able to pass through a meter of water at unvegetated sites in May than vegetated sites.

Australia’s oceans provide many economic and environmental benefits both nationally and regionally, and are of particular social, recreational and cultural importance. Western Australia's most intensively used marine embayment is Cockburn Sound, is Cockburn Sound, it supports one of the most extensive Posidoni seagrass communities in Western Australia. The protected coastal waters off the southern metropolitan coastline of Perth arc utilised intensively for industrial, commercial and recreational purposes. Over the past 50 years, wastes have been routinely discharged into Cockburn Sound causing extensive phytoplankton and epiphyte blooms, particularly during the 1960's and 1970's. The development of industrial and naval facilities and the intensification of landuses in the surrounding catchments over the past 50 years have together contributed to major losses of seagrass meadows in Cockburn Sound. Along with the contamination of biota, sediments and water, raising many concerns particularly for the future uses of the area. The Environmental Protection Authority (EPA) has expressed the view that industrial developments should not be considered in isolation, either from each other or existing activities but should be integrated in Cockburn Sound. Since the late 1970's, there have been reductions in the quantities of wastes discharged, however continued monitoring and the implementation of environmentally sustainable policies must continue, as Cockburn Sound remains in a delicate state of ecological balance. This study involved a detailed examination of the industrial development of Cockburn Sound since it began in 1953, and how this development significantly reduced Posidonia seagrass meadows. Original aerial photographs of Cockburn Sound in 5 year intervals since 1948 were used, and the study area of James Point was mapped to establish spatial and temporal patterns in Posidonia seagrass meadows. These patterns were further defined by grouping them into 5 distinct 10 year periods. These 5 periods grouped spatial and temporal patterns which were found to be most pronounced between 1960 and 1975 This destructive period accounted for 85 % of seagrass loss in Cockburn Sound, mainly from the combined physical (man-made) and chemical effects. These losses immediately commenced with the industrialisation of Kwinana in 1953, and as a consequence the physical destruction of large inshore seagrass meadows for the construction of groynes, jetties and marina's resulted. The 1960's and 1970's decades are characterised by the chemical (particularly nutrient) discharges into Cockburn Sound as a result of heavy industries which had been established in the Kwinana lndustrial Area during the 1950's. Large amounts of nitrogen and phosphorous entered the Sound from the slow release of sediments and heavily impacted upon seagrass meadows. From this study Posidoni seagrass meadows were found to be lost due to the destructive effects of the industrialisation, and that by the end of the 1970's almost all seagrass meadows had been effected. Dramatic seagrass movements occurred and the expanding industrial and residential sectors greatly impacted upon their distributions. The further loss of whatever seagrass meadows that still occur in Cockburn Sound may seem inevitable, but once meadows have been lost they do not easily recolonise, if at all. Therefore incorporating ecologically sustainable development measures should be an immediate priority in such an already heavily degraded marine environment.

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans(PCDFs) are two groups of lipophilic, persistent organic pollutants that are produced as by-products of various anthropogenic and industrial processes. Due to their relatively high toxic potencies and potential to bioaccumulate and biomagnify in organisms and through the food chain, the contemporary widespread distribution of these compounds is a concern to the health of the environment, wildlife and humans. This study determined the distribution, pathways and fate of PCDD/Fs in the coastal zone of Queensland, Australia, including the inshore marine environment of the World Heritage Great Barrier Reef Marine Park. This ecosystem supports unique fauna and flora such as the marine herbivorous mammal dugong (Dugong dugon) and its food source, seagrass. Elevated PCDD/Fs were present in soils and sediments along the entire Queensland coastline. Highest concentrations were found in soil from agricultural irrigation drains and in sediments near the mouths of major rivers. Elevated concentrations were associated with rural and urban types of land-use, and PCDD/Fs were present even in locations remote from anthropogenic activities. PCDD/F congener-specific analysis revealed an unusual profile in all samples, dominated by OCDD, with PCDFs present in low concentrations or below the limit of detection. Distinct HxCDD isomer patterns were observed, with the 1,2,3,7,8,9-HxCDD/1,2,3,4,6,7-HxCDD isomer pair dominating the 2,3,7,8-substituted HxCDDs. Similar congener and isomer characteristics were reported in sediments, soil and clay samples from other continents, but could not be attributed to any known source. Possible PCDD/F sources in Queensland were assessed using segmented estuarine sediment cores, for which radiochemical chronologies were established for each depth. Variations of PCDD/F concentrations in the sediment cores over several centuries of depositional history were relatively small. Elevated PCDD levels were still present in sediment slices from the early 17th century. PCDD/F homologue profiles in sediments deposited during the last 350 years were almost identical and correlated well to the characteristic profiles observed in surface sediments and soils from the entire Queensland coastline. These results suggested the presence of an unidentified PCDD source prior to the production of commercial organochlorine products. To investigate the formation of the unusual PCDD/F profiles, congener and isomer specific analyses were undertaken in soils, sediments and dated sediment cores. The results demonstrated that specific transformation processes in the environment have resulted in the observed PCDD profile characteristics. Dechlorination of OCDD was proposed to result in distinct 1,4-pattern characteristics (i.e. formation of isomers chlorinated in the 1,4,6,9-positions). Consequently, the environmental samples do not reflect the signatures of the original source. An alternative hypothesis to natural formation is discussed evaluating these processes and their implications for possible source contributions. This hypothesis explores the potential for the influence of anthropogenic PCDD precursors (e.g. pentachlorophenol) during the 1940s to 1990s. Transport of PCDD/Fs from the land-based source via impacted tributary river systems, and subsequent deposition processes are proposed to result in PCDD/F accumulation in the inshore marine ecosystem. The extent of the sediment PCDD/F contamination governs the concentrations in the extensive inshore marine seagrass meadows of Queensland. Partitioning processes in the sediment-seagrass system lead to increased toxic equivalency (TEQ) in the seagrass, compared to sediment.The relationship between contaminated inshore sediments, seagrass and dugongs were evaluated using six dugong habitat regions along the coastline. PCDD/F body burdens in dugongs are governed by sediment (and seagrass) PCDD/F concentrations in their habitat. High seagrass (and incidental sediment) ingestion rates, selective retention of toxicologically potent congeners and relatively low PCDD/F elimination capacities in dugongs are proposed to result in elevated PCDD/F concentrations and TEQ levels in adult animals. Transfer efficiencies of 4 and 27% of maternal TEQ levels to foetuses and calves (respectively) during gestation and lactation result in relatively high exposure potentials to offspring. Compared to no-observed-adverse-effect-levels in other mammals, and based on the results of this study, a tolerable daily intake (TDI) of 10-24 pg TEQ kg-1 day-1 was estimated for dugongs. The results of the present study found that dugongs from some regions along the coastline of Queensland exceed this TDI by up to 20 fold, suggesting that these populations may be at risk from PCDD/F contamination in their habitat. These results have important implications for the health of the environment, wildlife and humans and were used to develop a conceptual understanding of the sources, pathways and fate of dioxins in Queensland, Australia.

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans(PCDFs) are two groups of lipophilic, persistent organic pollutants that are produced as by-products of various anthropogenic and industrial processes. Due to their relatively high toxic potencies and potential to bioaccumulate and biomagnify in organisms and through the food chain, the contemporary widespread distribution of these compounds is a concern to the health of the environment, wildlife and humans. This study determined the distribution, pathways and fate of PCDD/Fs in the coastal zone of Queensland, Australia, including the inshore marine environment of the World Heritage Great Barrier Reef Marine Park. This ecosystem supports unique fauna and flora such as the marine herbivorous mammal dugong (Dugong dugon) and its food source, seagrass. Elevated PCDD/Fs were present in soils and sediments along the entire Queensland coastline. Highest concentrations were found in soil from agricultural irrigation drains and in sediments near the mouths of major rivers. Elevated concentrations were associated with rural and urban types of land-use, and PCDD/Fs were present even in locations remote from anthropogenic activities. PCDD/F congener-specific analysis revealed an unusual profile in all samples, dominated by OCDD, with PCDFs present in low concentrations or below the limit of detection. Distinct HxCDD isomer patterns were observed, with the 1,2,3,7,8,9-HxCDD/1,2,3,4,6,7-HxCDD isomer pair dominating the 2,3,7,8-substituted HxCDDs. Similar congener and isomer characteristics were reported in sediments, soil and clay samples from other continents, but could not be attributed to any known source. Possible PCDD/F sources in Queensland were assessed using segmented estuarine sediment cores, for which radiochemical chronologies were established for each depth. Variations of PCDD/F concentrations in the sediment cores over several centuries of depositional history were relatively small. Elevated PCDD levels were still present in sediment slices from the early 17th century. PCDD/F homologue profiles in sediments deposited during the last 350 years were almost identical and correlated well to the characteristic profiles observed in surface sediments and soils from the entire Queensland coastline. These results suggested the presence of an unidentified PCDD source prior to the production of commercial organochlorine products. To investigate the formation of the unusual PCDD/F profiles, congener and isomer specific analyses were undertaken in soils, sediments and dated sediment cores. The results demonstrated that specific transformation processes in the environment have resulted in the observed PCDD profile characteristics. Dechlorination of OCDD was proposed to result in distinct 1,4-pattern characteristics (i.e. formation of isomers chlorinated in the 1,4,6,9-positions). Consequently, the environmental samples do not reflect the signatures of the original source. An alternative hypothesis to natural formation is discussed evaluating these processes and their implications for possible source contributions. This hypothesis explores the potential for the influence of anthropogenic PCDD precursors (e.g. pentachlorophenol) during the 1940s to 1990s. Transport of PCDD/Fs from the land-based source via impacted tributary river systems, and subsequent deposition processes are proposed to result in PCDD/F accumulation in the inshore marine ecosystem. The extent of the sediment PCDD/F contamination governs the concentrations in the extensive inshore marine seagrass meadows of Queensland. Partitioning processes in the sediment-seagrass system lead to increased toxic equivalency (TEQ) in the seagrass, compared to sediment.The relationship between contaminated inshore sediments, seagrass and dugongs were evaluated using six dugong habitat regions along the coastline. PCDD/F body burdens in dugongs are governed by sediment (and seagrass) PCDD/F concentrations in their habitat. High seagrass (and incidental sediment) ingestion rates, selective retention of toxicologically potent congeners and relatively low PCDD/F elimination capacities in dugongs are proposed to result in elevated PCDD/F concentrations and TEQ levels in adult animals. Transfer efficiencies of 4 and 27% of maternal TEQ levels to foetuses and calves (respectively) during gestation and lactation result in relatively high exposure potentials to offspring. Compared to no-observed-adverse-effect-levels in other mammals, and based on the results of this study, a tolerable daily intake (TDI) of 10-24 pg TEQ kg-1 day-1 was estimated for dugongs. The results of the present study found that dugongs from some regions along the coastline of Queensland exceed this TDI by up to 20 fold, suggesting that these populations may be at risk from PCDD/F contamination in their habitat. These results have important implications for the health of the environment, wildlife and humans and were used to develop a conceptual understanding of the sources, pathways and fate of dioxins in Queensland, Australia.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Public Health
Faculty of Health Sciences
Full Text

The ongoing threat of seagrass loss from reduced light availability, coupled with our lack of knowledge of associated trophic responses has motivated this characterization of the flow-on effects of light reductions to Amphibolis griffithii seagrass fauna. Recently, field manipulations of varying light reductions, induced disturbances in a A. griffithii seagrass meadow that have been shown to effect potential food resources and the structural complexity of seagrass habitats for macroinvertebrates. This offered the opportunity to assess the flow-on effects to seagrass for fauna, a topic that has seldom been examined. This study investigated the effects of different light reduction intensity (high: ~92% reduction; moderate: ~84% reduction), duration (3, 6 and 9 mo) and timing (post-winter and post-summer) on the density, biomass and community composition of macroinvertebrate epifauna within an A. griffithii seagrass ecosystem (Western Australia). Shade structures, placed within a healthy A. griffithii meadow, were used to create the light reduction treatments. Following shading, there were significant interactions between all three light reduction factors, and generally there was decline in the density and biomass of fauna (between 38% and 89% in density) and the number of families with increasing duration and intensity of light reduction (between 11 and 53% fewer families in light reduction treatments). There was also an effect of time, with taxa abundance and family composition Post-summer differing to Post-winter.