Littérature scientifique sur le sujet « Sandy beaches, littoral macrofauna »

Using data available from the literature, patterns of biomass, production and productivity of sandy-beach macrofauna populations were examined, considering environmental (temperature, exposure, grain size and beach slope) and biological variables (life span and mean body mass) and feeding and taxonomic groups. A total of 102 estimates of both production and biomass and 105 estimates of P/B ratios were collected from 52 studies carried out between 42°46′S and 54°05′N, for 83 sandy-beach macrofauna populations. The negative relationship between P/B ratio and beach slope for the supralittoral amphipods agrees with the Habitat Safety Hypothesis, according to which these forms would show higher mortality in dissipative than in reflective beaches. The observed higher production of filter-feeders in exposed than in sheltered beaches suggests that more food is available for filter-feeders in exposed beaches. The higher production of filter-feeders (represented by bivalves and decapods), than of scavengers/predators (peracarids and gastropods) showed the importance of filter-feeders in the food web of sandy beaches. The P/B ratios were strongly related to life span, but weakly or not related to the mean body mass. The high amphipod P/B ratio was attributed to the short life span of these crustaceans; conversely, gastropods showed the lowest P/B ratio, in accordance with their longer life span. The observed differences in biomass, production and P/B ratios within crustaceans and molluscs were attributed to differences in life-history traits and feeding mode.

The role of morphodynamic features such as grain size, swash climate and wave action on the macrofauna of beaches are well-known. However, few studies have investigated natural disturbances as potential drivers of temporal community variations. In southeastern Brazil, we sampled the intertidal macrofauna of two sandy beaches to test whether seasonal disturbances as the frequency of storm wave events (SWE) and rainfall have significant influence on their composition and abundance. The macrofauna assemblage differed significantly between the rainy and the dry seasons, but rainfall was not the main driver of community changes, although both beaches are in the vicinity of extensive river plumes. Actually, SWE explained most macrofauna richness overtime, with positive effects. Our results point to the importance of learning more about the effects of poorly studied disturbances on macrofaunal communities, and based on them we strongly recommend including these seasonal phenomena when monitoring sandy beaches.

The role of morphodynamic features such as grain size, swash climate and wave action on the macrofauna of beaches are well-known. However, few studies have investigated natural disturbances as potential drivers of temporal community variations. In southeastern Brazil, we sampled the intertidal macrofauna of two sandy beaches to test whether seasonal disturbances as the frequency of storm wave events (SWE) and rainfall have significant influence on their composition and abundance. The macrofauna assemblage differed significantly between the rainy and the dry seasons, but rainfall was not the main driver of community changes, although both beaches are in the vicinity of extensive river plumes. Actually, SWE explained most macrofauna richness overtime, with positive effects. Our results point to the importance of learning more about the effects of poorly studied disturbances on macrofaunal communities, and based on them we strongly recommend including these seasonal phenomena when monitoring sandy beaches.

Several studies have been conducted to explain patterns of the abundance, richness and diversity of sandy-beach macrofauna; however, such analyses have ignored the overall functional structure of macrofauna communities. Few studies have examined polychaete feeding guilds on sandy beach environments. To examine the effects of environmental factors on polychaete feeding guilds on sandy beaches, 12 sandy beaches from five islands in Sepetiba Bay were sampled. A total of 24 polychaete morphospecies, grouped among 21 families, were identified in these sandy beaches. The polychaete species were classified into 10 feeding guilds, and the SDT guild (suspended-deposit feeders, discretely motile, with tentacles) was the most abundant feeding guild, with 34.2% of total number of organisms. The highest trophic importance index and index of trophic diversity values were recorded on the sheltered beaches. A canonical correspondence analysis showed that the exposure rate, beach length, and grain size of the beach sediment significantly affected the polychaete feeding guild distribution and abundance. We can conclude that sheltered beaches have a higher diversity of feeding guilds than exposed beaches and that the biological descriptors of the feeding guilds are directly associated with the grain size of the sediment.

The state of the art of the studies on the production of Brazilian sandy beach macrofauna was analyzed on the basis of the data available in the literature. For this purpose, the representativeness of the production dataset was examined by latitudinal distribution, degree of exposure and morphodynamic state of beaches, taxonomic groups, and methods employed. A descriptive analysis was, further, made to investigate the trends in production of the more representative taxonomic groups and species of sandy beach macrofauna. A total of 69 macrofauna annual production estimates were obtained for 38 populations from 25 studies carried out between 22º56'S and 32º20'S. Production estimates were restricted to populations on beaches located on the southern and southeastern Brazilian coast. Most of the populations in the dataset inhabit exposed dissipative sandy beaches and are mainly represented by mollusks and crustaceans, with a smaller number of polychaetes. The trends in production among taxonomic groups follow a similar pattern to that observed on beaches throughout the world, with high values for bivalves and decapods. The high turnover rate (P/B ratio) of the latter was due to the presence of several populations of the mole crab Emerita brasiliensis, which can attain high values of productivity, in the dataset. Most of the studies focus on the comparison of production and, especially, of P/B ratio according to life history traits in populations of the same species/taxonomic group. Despite the importance of life history-production studies, other approaches, such as the effect of man-induce disturbances on the macrofauna, should be undertaken in these threatened environments.

Abstract Sandy beaches are dynamic ecosystems with strong interaction of sediments, waves and tidal energy, with marked effects on benthic assemblages. Although there are numerous efforts in understanding spatial-temporal variation of benthic macrofauna on sandy beaches along the southern and southeastern Marine Ecoregions in Brazil, there is poor sampling along beaches of the Eastern Marine Ecoregion (EME). Here we examined spatial and temporal scales of variability in benthic macrofauna (> 500 µm) through a hierarchical sampling of two dissipative sandy beaches within the EME between two seasons (winter 2011 and summer 2012). We tested the hypothesis that spatial changes (i.e., meters to hundreds of meters scales) in the structure of benthic assemblages will be more pronounced compared to the weak seasonal fluctuations at this tropical region. We found weak temporal and spatial changes in sediment grain size and beach slope, but differences in macrofaunal assemblages were evident. Contrary to our hypothesis, hierarchical sampling indicated significant changes in macrofaunal composition and density at multiple local scales (meters to hundreds of meters) and on seasonal scales. The macrofauna density and composition was directly related to changes on the sediment organic matter and grain size.

Sandy beaches provide several ecosystem services such as coastal protection and resilience, water filtration and nutrient mineralization. Beaches also represent a hub for social, cultural and economic relationships as well as educational activities. Increasing urbanization, recreational activities and mechanical beach cleaning represent major anthropogenic disturbances on sandy beaches leading to loss of biodiversity as well as good and services. Information about the impacts of anthropogenic pressures on benthic macrofaunal communities could be useful to assess the environmental status of sandy beaches and to promote a sustainable use of beach ecosystem. Here, scientific articles about three major anthropogenic impacts on sandy beach macrofauna were reviewed to provide the state of knowledge about these impacts, to highlight gaps, to supply considerations about the methodologies and the used indicators and to give insights for future studies. The stressors considered in our review are: 1) trampling, 2) breakwater barriers, 3) mechanical beach cleaning. This review underlined that there are few studies regarding individual human disturbances on sandy beach macrofauna and specifically, there is a lack of sufficient indicator species for the assessment of such stressors. Similarly, the researches have covered specific regions, highlighting the need for such studies in other parts of the world. In particular, the impacts of breakwater barriers on surrounding communities has been found to be given less attention in the literature and there is enough that could be explored.

Three exposed sandy beaches were selected to compare fluctuations in density of the most abundant species, and to verify the influence of spatial and temporal variations on the community structure. Sampling was carried out every three months, from June 1993 to May 1995, on Fora, Prainha, and Boqueirão Beaches. The first two beaches were classified by Dean's morphodynamic index (Ω) as intermediate, and the last as reflective. Slope, beach width and median grain size were significantly different among the beaches. Two-way analysis of variance revealed significant differences in species richness only among the beaches. No significant differences in density of the macrofauna between beaches and season were observed. However, Prainha Beach showed a higher temporal variation of the density of the macrofauna (and higher standard deviation) than the other two beaches. Emerita brasiliensis (Crustacea: Decapoda), Excirolana braziliensis (Crustacea: Isopoda), and Pseudorchestoidea brasiliensis (Crustacea: Amphipoda) were the most abundant species. Canonical correspondence analysis calculated the influence of the temporal variation as 27·5%; the influence of the environmental variation on community structure was 20·9%. The results suggest that in spite of the long-term fluctuations in species density, the beaches did not have temporal differences in the species richness and total density macrofauna during the study period.

The spatial distribution of benthic macrofauna on the beaches of Tramandaí, Jardim do Éden and Harmonia, was investigated over five consecutive days in April, 2003. The distribution pattern was also analyzed along with environmental parameters. Three transects were set on each beach, 50 m apart, with four sample stations set along each transect. On every station, three samples of benthic macrofauna were taken daily, with a core sampler with 20 cm diameter. In the midlittoral zone, the polychaete Euzonus furciferus and the isopod Excirolana armata dominated. In the swash zone, tidal migrators, Emerita brasiliensis,Donax hanlevanus and Mesodesma mactroides, were the most abundant species and, on some days, the polychaete Scolelepis gaucha. In the lower zones of the beaches, D. hanleyanus,M. mactroides and the amphipod Puelche orensani dominated. This zonation pattern was found for all three studied beaches, based on the average density of each species, over the five days period. Horizontal variation in the fauna was not found, either inter or intra the studied beaches, possibly due to little variability in slope and homogeneity of sediment grain size presented in the three beaches.

Bibliography: leaves 188-199.
Previous sandy beach research described beach macrofaunal communities according to the swash exclusion hypothesis (SEH). This hypothesis stated that more species are present on fine grained, flat dissipative beaches due to a more benign swash climate. It suggested that, as beach morphodynamics change to reflective conditions, which is experienced on coarse, steep beaches, few species can survive; these beaches are therefore characterised by lower macrofaunal diversities, abundance and biomass. Furthermore, little proof has been obtained of biological interactions such as competition or predation, and beaches have been described as physically controlled environments. The aim of this investigation was therefore to redifine the SEH in more specific terms, preferably into a form that is experimentally testable, and to find evidence of biological interactions that could be important enough to modify/explain population or community structures. Furthermore, the study aimed to find experimental procedures to serve as alternatives to the previously correlative type approach.

Accumulations of seagrass, macroalgae and other matter, collectively known as wrack, commonly occur on many sandy beaches, and can play an important role in coastal and nearshore ecosystems. Despite this, wrack removal from sandy beaches is a widespread and increasingly common practice globally, and there is little information regarding the ecological effects of such wrack removal on sandy beaches. The aim of this thesis was to establish the ecological importance of wrack in South Australian (SA) sandy-beach ecosystems. As a first step in furthering our understanding of the effects of wrack removal, I aimed to assess the importance of wrack, independent of the effects of wrack removal. The second over-riding aim of this thesis was to assess the ecological effects of wrack removal on aspects of these systems. To date, the methods used for quantifying the size of wrack deposits on sandy beaches have had limited use due to the time and expertise required to conduct thorough sampling. In Chapter 2, I thus tested the accuracy of a rapid “photopoint” method to visually estimate percentage wrack cover as well as provide an archived record. Comparisons of results obtained from conventional transects with those from photopoints indicated that the photopoint technique can be used to rapidly and accurately estimate % wrack cover on sandy beaches. The photopoint method has a wide range of potential applications and represents a valuable advance in the field. Currently our knowledge of the amounts and types of wrack on SA shores is limited, despite these accumulations being a feature of some SA beaches. Wrack deposits in three biogeographical regions of SA were thus repeatedly surveyed to assess spatial (between and within regions) and temporal (seasonal and inter-annual) variation (Chapter 2). Both wrack cover and the composition of wrack deposits varied spatially and temporally. Wrack deposits contained a diverse array of seagrass, algal, other biotic materials and anthropogenic debris. The South East region of SA had distinctly-different wrack deposits compared to the Metropolitan and Fleurieu Peninsula regions; in general, the cover of wrack was higher, and the diversity and biomass of kelps, red algae and green algae was higher in this region compared to the other two regions. South Australian wrack deposits are thus dynamic and complex. The amount of wrack deposited and retained on a beach may be affected by the beach morphology but, to date, few studies have investigated this link. I assessed wrack cover on beaches with a range of morphodynamic types and found that beaches that were more dissipative in nature had a greater cover of wrack than beaches of the reflective type. I also examined whether wrack deposits affected the sediment characteristics of underlying and nearby sediments. Wrack deposits had little measurable effect on underlying sediments and did not affect particle-size distribution or organic-matter content. There was, however, a trend for beaches in the South East region of SA to have higher organic matter content in their sediments, and these beaches also have higher wrack cover and higher proportions of algae in their deposits. There was also a trend for beaches with higher wrack cover to have less compacted sediments, although this trend was not consistent. Overnight pit-fall trapping surveys of the macrofauna on four SA sandy beaches indicated that local macrofaunal communities were diverse (representing 72 species from 19 Orders in total), abundant, and variable in both time and space. The macrofauna encountered were mostly terrestrial taxa with only 2 truly marine species, and spanned multiple trophic levels, concurring with the results of previous studies. Macrofaunal abundances were higher where associated with wrack than in bare sand, and macrofaunal communities differed between the driftline of wrack and wrack patches away from the driftline. Within the driftline itself, there were few differences between bare sand and wrack-covered areas, suggesting that the entire driftline area is important as a habitat and food resource. Thus, wrack deposits provide an important habitat and food source for macrofauna, and the driftline provides an area of beach with concentrated resources, which in turn concentrates a distinct macrofaunal community. Wrack deposition on sandy beaches varies spatially and is affected by morphological features on the beach-face such as cusps. In Chapter 5, I thus tested a series of hypotheses regarding the differences in wrack deposits, sediments and macrofaunal communities between cusp bays and horns. Bays had greater cover and larger pieces of wrack than horns. Sediment organic-matter content was greater on horns than in bays but mean particle size did not differ consistently between bays and horns. Macrofaunal diversity was higher in bays and this pattern was probably driven by differences in the cover of wrack between bays and horns. Cusp morphology thus influences the distribution of wrack on the beach-face, which in turn influences the distribution of macrofauna. Studies of sandy beaches with cusps should therefore be explicitly designed to sample cusp features and their associated wrack deposits. Chapter 6 assesses the incorporation of wrack into beach and nearshore ecosystems via two pathways: decomposition and incorporation into trophic webs. I assessed the decomposition of algal and seagrass wrack using litterbag experiments and found that after a very rapid initial loss of mass, likely due to cell lysis and leaching, the rate of decomposition of wrack was much slower. Most release of nutrients from organic matter decay thus appears to occur in the first few days after deposition and the processes affecting the rate and nature of wrack decomposition vary among taxa (i.e. algal versus seagrass and among species). Stable isotopes of C and N were used to assess whether beach macrofauna or nearshore macro-invertebrates and fish might rely on wrack as a source of nutrition. I found that seagrasses did not provide a food source for any consumers but algae, particularly brown algae including kelps, appeared to be potential sources of nutrition for beach and nearshore consumers. The incorporation of wrack into beach and nearshore ecosystems may thus occur primarily through consumption of algal wrack by herbivores such as amphipods and dipterans, with predation on them being important pathways for the transfer of nutrients and energy into higher trophic levels. The amount of wrack in the surf zone did not affect the abundance and species richness of fish and invertebrates netted there. The aim of Chapter 7 was to determine the effects of wrack removal on sandy beach macrofaunal communities. In the first study the effects of large-scale commercial harvest of wrack on the macrofaunal communities at Kingston were assessed. The macrofaunal communities present in the ‘Natural’ area of Kingston beach were far more diverse and abundant, and included different species, compared to the ‘Cleared’ area at Kingston. In the second part of Chapter 7, I experimentally removed wrack from the driftline of beaches to assess short-term effects on macrofaunal communities. The experimental treatment did not appear to have any measurable effects on the macrofaunal communities. I also analysed material that was removed from the beach in the raking experiments and found that a large proportion of the material (e.g. 81% of the DW) was sand. I recommend that future studies into the effects of wrack removal use large cleared areas of beach, attempt to use the same wrack removal methods and/or machinery used locally, and assess the macrofaunal communities repeatedly and over longer times following wrack removal activities. In Chapter 8, I attempt to assess the effects of removal of wrack for beach ‘cleaning’ or commercial ‘harvest’ of wrack by comparing key indicators from Chapters 2 to 7. Implications and recommendations for the management of wrack are discussed, including with regard to the techniques used in this thesis and their applicability in managing wrack deposits. I attempt to identify the shortcomings of this research as well as directions for further research. Thus I have demonstrated that wrack in SA provides an important link between offshore habitat and nearshore, beach and terrestrial habitats via the transfer of organic matter and nutrients. Wrack interacts with beach morphology and sediments, provides habitat for macrofauna, remineralises nutrients through its decomposition, and provides the basis of a complex trophic web. I conclude that wrack is a key component in beach ecosystems.

Le spiagge sabbiose sono uno dei luoghi più importanti, non solo in quanto sostengono la biodiversità fornendo habitat e cibo, ma anche aiutando il sostentamento umano fornendo opportunità socioeconomiche. La crescente pressione sulle spiagge sabbiose sta portando al degrado dell'ecosistema costiero. Per comprendere queste minacce e il loro impatto sulle comunità macrobentoniche intertidali, è stato svolto questo progetto. Inizialmente, i dati relativi a determinati impatti umani sono stati raccolti a livello globale sotto forma di una revisione sistematica per evidenziare le lacune. I dati relativi agli impatti delle perturbazioni antropiche sul Mare Adriatico sono risultati molto limitati. Le attività del progetto sono state condotte in tre fasi dove nella prima fase sono state studiate 2 spiagge per un anno con cadenza mensile. Nella seconda fase, 4 spiagge sono state studiate su base stagionale (tre volte). Nella terza fase sono state studiate 5 spiagge solo intorno alla stagione estiva per valutare l'impatto del turismo estivo. Nelle ultime 2 fasi del progetto, sono stati presi in considerazione anche i blocchi relativi al COVID-19 poiché l'uso delle spiagge era limitato. Differenze complessivamente significative sono state riscontrate tra la macrofauna appartenente a differenti taxa. Le differenze sono probabilmente legate alla differenza nel tipo di impatto in siti diversi. Complessivamente, nella maggior parte dei siti i bivalvi appartenenti principalmente a Lentidium mediterraneum sono risultati essere i taxa più dominanti nei siti colpiti. Nei siti con meno disturbi, Donax sp. è stato trovato più comunemente alludendo a una maggiore sensibilità ai disturbi umani. Il gasteropode Tritia neritea è risultato essere uno degli organismi resistenti alle perturbazioni in quanto raggiungevano il picco di abbondanza nel periodo più turistico. Inoltre, i crostacei come gli anfipodi sono stati trovati maggiormente in siti meno colpiti e/o stagioni/periodi meno colpiti, evidenziando il loro potenziale come indicatore di disturbi negli ecosistemi delle spiagge sabbiose. Sebbene, in ambiente naturale, potrebbe diventare più complesso separare un tipo di impatto su un determinato taxon da un altro, i nostri risultati possono indicare alcune informazioni riguardanti la sensibilità di un particolare taxa rispetto a un impatto specifico.
Sandy beaches are one of the most important spots that is not only sustaining biodiversity by providing habitat and food but also supporting human livelihood by providing socioeconomic opportunities. The increasing pressure on sandy beaches is leading to degradation of coastal ecosystem. To understand these threats and their impacts on the intertidal macrobenthic communities, this project was designed. Initially, data regarding certain human impacts was collected globally in the form of a systematic review to highlight the gaps. The data regarding impacts of anthropogenic disturbances on Adriatic Sea was found to be very limited. The activities of the project were conducted in three phases where 2 beaches were studied for one year on monthly basis in the first phase. In the second phase, 4 beaches were studies on seasonal basis (three times). In the third phase, 5 beaches were studied only around the summer season to evaluate the impact of the summer tourism. In the later 2 phases of the project, the COVID-19 related lockdowns were taken into account as well since the use of the beaches was limited. Overall significant differences were found among the macrofauna belonging to different taxa. The differences are possibly related to the difference in the type of impacts at different sites. Overall, at most of the sites bivalves mainly belonging to Lentidium mediterraneum was found to be the most dominant taxa at impacted sites. At sites with less disturbances, Donax sp. was found more commonly hinting about its sensitivity towards human disturbances. The gastropod specifically Tritia neritea was found to be one of the resistant organisms towards disturbances since they were peaking in abundance at the most touristic period. Furthermore, the crustaceans such as amphipod were found more at less impacted sites and/or less impacted seasons/periods, highlighting their potential as an indicator of disturbances in sandy beach ecosystems. Although, in natural environment, it could become more complex to segregate one type of impacts on a certain taxon from another, yet our detailed results can indicate some information regarding the sensitivity of a particular taxa towards a particular impact.

Sandy beaches are often highly allochthonous, depending on external subsidies of carbon and nutrients. Despite this, sandy beach macrofaunal assemblages have received little attention regarding their response to enhanced primary productivity generated from coastal upwelling. This thesis investigates the influence of upwelling on macrofaunal assemblages over a variety of spatial and temporal scales. Spatially, four regions were examined across two biogeographic provinces to remove temperature as a confounding factor, and limit biogeography-specific effects. A nested hierarchical design enabled both large and small scales to be examined and generalities about upwelling effects across multiple areas to be considered. Sampling was conducted in two seasons, and over two years, to test the persistence of any effects. Biogeography and region had the strongest influences on macrofaunal biodiversity. Upwelling influenced macrofaunal assemblages in every region when analyses were conducted at the species level. However, the particular effect, positive or negative, differed among regions depending on local factors, and between the response variables, abundance and biomass. Coarser scales of taxonomy, feeding guild and developmental mode were investigated; however, the influence of upwelling generally became weaker and more varied, and occasionally disappeared. Seasonality was greater on the South Coast but was still important in some analyses on the West Coast. At the small-scale, variation within-beaches was lower than between beaches, assemblage structure remained stable over time, and consistent zonation was not present. The influence of temperature on filtration rate and oxygen consumption of Donax serra was investigated to test a driving mechanism for assemblage responses to upwelling. Feeding ability was significantly reduced at colder temperatures indicating an important factor which may be involved in determining assemblage structure. These results suggest that alterations to upwelling regimes predicted under climate change scenarios will impact sandy beach macrofauna, however the specific outcome will depend on multiple contextual factors.

Longshore sediment transport rate was measured during energetic sea breeze activity, on intermediate-to-reflective sandy beaches in Southwestern Australia. Estimates of suspended load were obtained using backscatter sensors, current meters and streamer traps. Total load was determined using fluorescent tracer sand and an impoundment study. The measurementsw ere cross-compareda nd usedt o evaluates everalw idely-used longshore transport equations. The streamer trap measurement revealed an exponential distribution of the suspended sediment flux with vertical mixing decreasing in the onshore direction. A continuous time series of the longshore suspended sediment flux across the surf zone was obtained by combining the streamer trap measurements with data collected using surf zone instruments. Comparison of the suspended longshore flux with the total longshore flux derived from the dispersal of the sand tracer indicated that the relative contribution of the suspendedlo ad to the total load was at least 59 %. The movement of sandt racer on four different beaches demonstrated that nearshore sediments were transported obliquely across the surf zone, challenging our conventional view of dividing nearshore sediment transport into cross-shore and longshore components. Furthermore, tracer was found to move from the outer surf zone to the swash zone and vice versa, indicating a cross-shore sediment exchange. The contribution of the swash zone to the total longshore flux was estimated around 30-40 %. Despite large differences in the temporal and spatial scales of the measurement techniques, the littoral drift rates are comparable, suggesting a northward transport rate of 138,000-200,000 m3 year-1. Longshore sediment transport during sea breezes is mainly the result of a high longshore energy flux exerted by wind waves. This is accurately predicted by the equations of Inman and Bagnold (1963) and CERC (1984). The bimodal wave field, characteristic of Southwestern Australia, renders the Kamphuis (1991b) formula unsuitable in this instance.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2006.
Submitted by Cristiane Gomides (cristiane_gomides@hotmail.com) on 2013-12-16T02:44:18Z No. of bitstreams: 1 PedrodeSa.pdf: 1303104 bytes, checksum: 596561a98d86d6219a45778a049ce092 (MD5)
Approved for entry into archive by Sabrina Andrade (sabrinabeatriz@ibest.com.br) on 2013-12-18T18:16:36Z (GMT) No. of bitstreams: 1 PedrodeSa.pdf: 1303104 bytes, checksum: 596561a98d86d6219a45778a049ce092 (MD5)
Made available in DSpace on 2013-12-18T18:16:36Z (GMT). No. of bitstreams: 1 PedrodeSa.pdf: 1303104 bytes, checksum: 596561a98d86d6219a45778a049ce092 (MD5) Previous issue date: 2006
Este trabalho objetiva avaliar a estrutura e dinâmica da associação de macroinvertebrados bentônicos da zona entremarés de dois locais com distintas características ambientais da praia do Cassino, RS, Brasil. O local 1 possui características de praia dissipativa extrema, sedimentos finos e baixa hidrodinâmica, enquanto que o local 2 características dissipativas/intermediárias, sedimento mais grosseiros e maior hidrodinâmica. Eventos esporádicos de deposição de lama são observados no local 1. Foi realizado um acompanhamento durante 14 meses (abril/04 até maio/05) com amostragens mensais. Os 2 primeiros meses foram considerados como piloto, sendo seus dados abordados no capítulo III. Em cada local, foram demarcadas três transversais (separadas por 50m) perpendicular a linha d’água, nas quais amostras foram coletadas em triplicata em 4 níveis (separados por 10 m). As transversais se estenderam desde 10m acima do varrido superior, até cerca de 1m de profundidade. No capítulo I, foi considerada a variabilidade temporal da associação. Esta apresentou uma marcada dinâmica, sendo as principais variações ligadas às dinâmicas populacionais e perturbações físicas. Durante o inverno foram observadas baixas densidades, as quais foram relacionadas à ausência de recrutamentos, deposição de lama em abril e embancamentos de baixas intensidades. Na primavera ocorreu explosão populacional de Scolelepis gaucha, migração de adultos de Mesodesma mactroides do infralitoral para a zona entremarés e um evento de embancamento. Durante o verão foram observados recrutamentos de M. mactroides, Donax hanleyanus e Emerita brasiliensis. O outono foi caracterizado por baixas densidades, exceto pelo recrutamento de D. hanleyanus. O capítulo II abordou a distribuição perpendicular à linha d’água e paralela à linha d’água da fauna em diferentes escalas. O local 2 apresentou maior diversidade do que o local 1. A diversidade foi maior provavelmente devido a presença dos anfípodes Phoxocephalopsis sp. e Plastyschnopidae, os quais estiveram praticamente ausentes no local 1. Verificou-se que praias dissipativas/intermediárias podem suportar maior diversidade da macrofauna bentônica do que as dissipativas extremas, possivelmente, pela capacidade da associação macrozoobentônica de se beneficiar da maior hidrodinâmica na zona de varrido. As diversidades menores no local 1, podem ainda, ser atribuídas as perturbações causadas pelas deposições esporádicas de lama. Através de análises multivariadas foram identificadas 3 zonas: o mesolitoral médio, o superior do varrido e o inferior do varrido juntamente com a arrebentação interna. As espécies características de cada zona variaram com a estação do ano. Foram observadas densidades decrescentes do mesolitoral em direção ao infralitoral. Não foram evidentes padrões de distribuição paralela à linha d’água na escala de dezenas de metros, devido a grande homogeneidade sedimentar registrada nesta escala. No capítulo III foram analisados com maiores detalhes dois eventos: mortalidade pós deposição de lama em abril/04 e embancamento em outubro/05. A recomposição da fauna mostrou-se bastante rápida, em ambos eventos, registrou-se a mesma composição após 3 meses, entretanto as populações foram caracterizadas por organismos juvenis e recém assentados. Sendo que a manutenção de estoques adultos foi afetada. A deposição de lama ocasionou a mortalidade de toda a associação. O evento de embancamento afetou, principalmente, os juvenis+adultos do bivalvo M. mactroides. É provável que esses eventos sejam o principal fator estruturador de longo prazo das associações destes locais.
The present study aims to analyze the structure and dynamics of the intertidal macrobenthic assemblages in two sites with distinct environmental characteristics of Cassino beach, RS, Brazil. Site 1 can be characterized as an extreme dissipative beach, with fine sediments and low hydrodynamics and site 2 is a dissipative/intermediate beach, with coarser sands and high hydrodynamics. Sporadic muddy deposition events occur in site 1. Sampling was conduct monthly from april/2004 to may/2005. Data from the fist two months was considered as a pilot study and was included just in chapter III. In each site, three transect lines, spaced 50 m apart, were defined perpendicular to the shore line, samples were collect in triplicate in 4 levels (10 m apart). Each transect was extend from 10 above de swash limit to 1m deep in the inner surf zone. Chapter I aimed to describe the temporal variability of the intertidal assemblages. A striking dynamics was recognized through samplings times. The mains temporal changes were influenced by the population dynamics of numerically dominants species and physical disturbances. In winter was found a low density and diversity of the assemblages, with were related to absence of recruitments, an event of muddy deposition and stranding events of low effects. In spring was observed a population explosion of the polychaeta Scolelepis gaucha, migration of Mesodesma mactroides adults from the subtidal to the intertidal and a strand event. During summer was observed recruitments of tidal migrant species as M. mactoides, Donax hanleyanus and Emerita brasiliensis. Fall was characterized by low densities, except for an expressive recruitment of D. hanleyanus. Chapter 2 aimed to describe the spatial distribution across shore and along shore in distinct scales. Site 2 showed a higher diversity than site 1. The higher diversity were probably due the presence of amphipods Phoxocephalopsis sp. and Plastyschnopidae in site 2, which were absent in site 1. The results showed that dissipative/intermediate can support higher diversities than extreme dissipative conditions, probably because the assemblage can be beneficiated by the higher hydrodynamics of swash. The low diversities found in site 1, may be also related to sporadic muddy deposition events. The multivariate analyses showed three macrofaunal zones: mesolitoral; the higher swash; the lower swash together with the inner surf zone. The characteristics species of each zone varied according to the season. A decrease of density was verified from mesolitoral zone to the lower levels. No patterns were identified in a smaller scale (50m) of the along shore distribution, probably due the high homogeneity of the morpho-dynamics and sediments in this scale. In Chapter III, the period that occurred two mortality events were analyzed with more detail: muddy deposition in april/2004 and stranding in october/2004. The recuperation of the macrofauna assemblages was extremely fast, in three months they showed the same composition, although the populations were characterized by high densities of recruitments and juvenis. The adult stokes may be heavily impacted by this events. The muddy deposition caused a mortality of all population of the intertidal assemblages. The bivalve M. mactroides juvenis+adults was the organism most affected by the strand event. It’s likely that these events are the main long term factors structuring this assemblage.

Praias arenosas são caracterizadas por uma abundante macrofauna, composta por poliquetas, moluscos e crustáceos. Dentre os moluscos, os gastrópodes constituem um dos grupos mais conspícuos. Entretanto, as informações sobre esse grupo em praias são escassas e se referem principalmente à ocorrência em comunidades. O neogastropoda Olivella minuta é comum e abundante em praias do Litoral Norte de São Paulo. Porém, há importantes lacunas no conhecimento quanto à distribuição desta espécie. Diante desse cenário, o presente estudo visou analisar a distribuição espaço-temporal de Olivella minuta na praia de Barequeçaba, bem como os fatores ambientais relacionados a essa distribuição. Para análise da distribuição espacial de O. minuta ao longo do entre-marés da praia, amostras foram obtidas em outubro de 2009, a partir de doze estações perpendiculares à linha da água, compostas por três transectos com seis níveis cada. Os fatores abióticos (características do sedimento) e bióticos (descritores da macrofauna) que compõem cada estação também foram amostrados e relacionados com a distribuição da espécie. Os resultados revelaram que os indivíduos ocorreram em maior densidade na porção sul da praia, e nos ambientes mais úmidos, próximos a linha da água. O carbonato de cálcio e a matéria orgânica foram os fatores mais determinantes, contrastando com a hipótese de que há influência tanto dos fatores abióticos quanto dos bióticos em tal distribuição. Para análise de distribuição temporal de Olivella minuta no eixo vertical da praia, amostras foram obtidas mensalmente no entremarés, a partir de cinco transectos aleatórios estabelecidos perpendicularmente à linha da água, com nove unidades amostrais. Além disso, amostras foram obtidas trimestralmente, no entremarés e infralitoral, a partir de cinco transectos aleatórios, compostos por nove e seis níveis amostrais, respectivamente. Os resultados revelaram um padrão de distribuição da espécie no entremarés ao longo do tempo, e confirmaram a hipótese de que há uma distribuição de O. minuta de acordo com o tamanho do indivíduos no eixo vertical da praia, com indivíduos menores ocorrendo apenas no infralitoral e migrando para o entremarés ao longo de sua ontogenia. Os avanços apresentados no presente estudo contribuem para o conhecimento sobre a ecologia de populações de praias arenosas, ao relacionar a distribuição de uma espécie da macrofauna com os fatores ambientais, e principalmente ao abranger o infralitoral nas amostragens, por tratar da distribuição de uma espécie cuja distribuição não é exclusiva do entremarés
Sandy beaches have typically abundant macrofauna, comprised of polychaetes, mollusks, and crustaceans. Among mollusks, gastropods comprise one of the most conspicuous groups. Nevertheless, data on this group for beaches are scarce and refer mainly to their occurrence in communities. The neogastropoda Olivella minuta is common and abundant on beaches along the Northern Coast of São Paulo. However, there are important gaps in the knowledge regarding the distribution of this species. Based on this scenario, the present study aims at analyzing the distribution of Olivella minuta in space and over time on Barequeçaba Beach, as well as the related environmental factors. To analyze the distribution of Olivella minuta along the intertidal zone of the beach, samples were obtained in October 2009 from twelve stations perpendicular to the waterline, comprised of three transects with six levels each. Abiotic (sediment characteristics) and biotic (macrofauna descriptors) factors that comprise each station were also sampled and linked to distribution. Results showed that there was higher density of individuals in the southern part of the beach, and in more humid environments, closer to the waterline. Calcium carbonate and organic matter were the most determining factors in the species\' distribution, as opposed to the hypothesis that both abiotic and biotic factors were influencing factors. To analyze the distribution of Olivella minuta over time in the vertical axis of the beach, samples were collected monthly in the intertidal zone, from five random transects set out perpendicularly to the waterline with nine sampling units. In addition, samples were also obtained quarterly with five random transects comprised of nine and six sampling levels in the intertidal zone and in the infralittoral zone, respectively. Results showed a distribution pattern for the species in the intertidal zone over time and confirm the hypothesis that O. minuta is distributed along the vertical axis of the beach according to the size of individuals, with smaller individuals occurring in the infralittoral and migrating to the intertidal zone throughout their ontogeny. Outcomes shown in the present study help improve the knowledge on population ecology of sandy beaches because they relate the distribution of a macrofauna species to environmental factors and mainly due to the fact that sampling covers also the infralittoral zone, since its distribution is not exclusive to the intertidal zone

Este estudo teve como objetivo estimar a produção secundária e a taxa de renovação (P/B) do gastrópode Hastula cinerea, do isópode Excirolana armata e dos decápodes Austinixa patogoniensis e Callichirus major na zona entremarés da praia do Una, situada na Estação Ecológica Juréia-Itatins, litoral sul do estado de São Paulo. Para essa finalidade, coletas mensais foram realizadas durante o período de dezembro/03 a novembro/05 em duas áreas, A (24°28,67’S e 47°07,36’W) e B (24°27,53’S e 47°05,86’W), no segmento norte da praia que apresenta estado morfodinâmico dissipativo. H. cinerea apresentou distribuição diferencial de acordo com o tamanho dos organismos entre as áreas, com predominância de indivíduos menores na área A, o que conduziu à maior abundância, produção (ca 0,18 g PSLC m-2 ano-1) e razão P/B nessa área. Baixas razões P/B dessa espécie (entre 0,8 e 1,3 ano-1) foram decorrentes de crescimento lento, ausência de indíviduos recém-recrutados na zona entremarés e falha no recrutamento no segundo ano de estudo. Essas baixas razões foram corroboradas pela alta expectativa de vida estimada para essa espécie (4,8 anos). As estimativas de produções de E. armata, restritas à área B, foram semelhantes entre machos e fêmeas, assim como entre os anos (ca 0,25 g PSLC m-2 ano-1). As P/B dos machos (entre 3,2 e 4,3 ano-1) foram superiores às das fêmeas (ca 3,1 ano-1), decorrentes dos menores comprimentos alcançados pelos machos. Altos valores de P/B de E. armata na praia do Una foram decorrentes de crescimento rápido que se refletiram em altas taxas de mortalidade (Z) e baixas expectativas de vida. Verificou-se uma correlação significativa e inversa entre a P/B e a expectativa de vida ao utilizar estimativas dos cirolanídeos E. armata e E. braziliensis obtidas em estudos de praias arenosas brasileiras. O caranguejo A. patagoniensis apresentou densidade média anual de 1 indivíduo.galeria-1 do talassinídeo C. major e de cerca de 6 indivíduos.m-2. Essas baixas densidades conduziram à reduzida biomassa e, conseqüentemente, a uma pequena produção, apesar das consideráveis taxas de renovação estimadas para esse braquiúro (ca 2,5 ano-1). C. major apresentou a maior produção (2,33 g PSLC m-2 ano-1) dentre as espécies estudadas. Ao considerar a ampla distribuição dessa espécie ao longo da face praial na área B (mais de 50 metros), na qual foi obtida a sua produção, a estimativa em faixa de metro linear (ca 130 g PSLC m-1 ano-1) foi a mais adequada para demonstrar a importância dessa espécie. A baixa razão P/B de C. major, 0,9 ano-1, indica reduzida capacidade de compensar sobrexploração, fato esse crítico para uma espécie freqüentemente extraída em praias brasileiras para utilização como isca. Ao analisar os métodos de produção da taxa de crescimento específica em peso (TCEP) e da freqüência de comprimento (FC), a partir de algumas estimativas de estudos de praias arenosas brasileiras e do presente estudo, verificou-se que esses tenderam a gerar estimativas similares. Os métodos empíricos analisados, entretanto, tenderam a sobreou subestimar acentuadamente as estimativas de produções, não fornecendo estimativas confiáveis. Com relação às interações tróficas, as razões isotópicas estáveis de carbono e nitrogênio dos consumidores na praia do Una evidenciaram que os hábitos alimentares das espécies/gêneros estão de acordo com os referidos na literatura, no geral, e que o ecossistema da praia do Una depende basicamente do material particulado em suspensão, apesar de indícios de que o microfitobentos também possa ter papel relevante na trama trófica dessa praia. As plantas das dunas, entretanto, aparentemente não contribuem como produtores primários nesse ecossistema.
This study has as objective to estimate the secondary production and turnover rate (P/B) of the gastropod Hastula cinerea, the isopod Excirolana armata and the decapods Austinixa patogoniensis e Callichirus major in the intertidal zone of Una beach, situated in Estação Ecológica Juréia-Itatins, on the southern coast of the state of São Paulo. For that purpose, monthly samplings were carried out during the period going from December/03 to November/05 in two areas, A (24°28,67’S and 47°07,36’W) and B (24°27,53’S and 47°05,86’W), in the northern segment of the beach, which presents dissipative morphodynamic state. H. cinerea presented differential distribution according to the individual sizes between the areas, with predominance of smaller individuals in area A, which led to the higher abundance, production (ca 0.18 g PSLC m-2 ano-1) and P/B ratio in this area. Low P/B ratios of this species (between 0.8 e 1.3 ano-1) were caused by slow growth, lack of newly recruited individuals in the intertidal zone and flaws in the recruitment in the second year of study. These low ratios were corroborated by the high life span estimated for this species (4.8 years). The production estimates for E. armata, limited to area B, were similar between males and females, as well as between the years (ca 0.25 g PSLC m-2 year-1). Male P/B (between 3.2 and 4.3 year-1) were superior to the female ones (ca 3.1 year-1), resulting from the smaller lengths reached by males. High P/B values for E. armata in Una beach resulted from its fast growth, which were shown in high mortality rates (Z) and low lifespans. A significant and inverse correlation between P/B and life span was verified as estimates obtained in studies of Brazilian sandy beaches for the cirolanidae E. armata and E. braziliensis were used. The crab A. patagoniensis presented an average annual density of 1 individual.burrow-1 for the talassinidae C. major and of approximately 6 individuals.m-2. These low densities led to the limited biomass and, consequently, to a small production, in spite of the considerable turnover rates estimated for this brachyurous (ca 2.5 year-1). C. major presented the highest production (2.33 g PSLC m- 2 year-1) among the studied species. When considering the vast distribution of this species along the beach face in area B (more than 50 meters), in which its production was obtained, the estimate in linear meter strip (ca 130 g PSLC m-1 year-1) was more appropriate to demonstrate the importance of this species. The low P/B ratio of C. major, 0.9 year-1, indicates limited capacity to compensate over exploration, which is critical for a species frequently extracted in Brazilian beaches to be used as bait. While analyzing the methods of production of specific growth rate in weight (SGRW) and of length frequency (LF), from some estimates in studies of Brazilian sandy beaches and in the present study as well, it was verified that the mentioned methods tended to generate similar estimates. The empirical methods that were analyzed, however, tended to strongly super or underestimate the production estimates, thus not providing reliable estimates. With relation to trophic relations, the stable isotopic ratios of carbon and nitrogen of consumers in Una beach made it evident that the feeding habits of the species/genders are in accordance with the ones referred to in literature, generally speaking, and that the Una beach ecosystem depends basically on the suspended particulate material, in spite of indications that microphytobenthos may also play a relevant role in the trophic web in this beach. The plants in the dunes, nevertheless, apparently do not contribute as primary producers in this ecosystem.

This thesis is composed of three separate chapters, two of which are published, an introductory and a concluding chapter. The main question that led to the development of the studies presented in the thesis is the following: is it possible to compare behavioural and ecological studies at a large geographical scale in the context of the ecosystems of sandy beaches under environmental changes? After the first introductory chapter, in the second chapter I present a review of studies in different (geographically distant) localities affected by similar distal and proximate drivers of climate change. In “Behavioural adaptations of sandy beach macrofauna in face of climate change impacts: A conceptual framework”, we discussed if behavioural responses by sandy beach macrofauna were consistent with expectations under climate change. We formulated specific hypotheses for how behavioural adaptations in sandy beach macrofauna are predicted to respond to climate change impacts. We provided an overview of macrofauna behavioural adaptation features in different and varying environmental contexts, a summary of the effects of main climate change drivers on sandy beaches and a conceptual framework predicting behavioural adaptations of sandy beach macrofauna under climate change pressure. In the third chapter, I present an experimental study linked to the main question for the ecological approach, to highlight which factors and variables in the physical-chemical environment influence the arthropodofauna distribution. In “Arthropodofauna richness and abundance across beach-dune systems with contrasting morphodynamics”, I investigated the across-shore distribution of arthropods in two Uruguayan sandy beach-dune systems with contrasting morphodynamics. I performed a deconstructive analysis to describe faunal changes from the dunes to the shoreline, and assessed existing hypotheses on the species distribution in relation to beach morphodynamics. In the fourth chapter, I present an experimental study focusing on talitrid ecology and behaviour in different localities, assuming that zonation and orientation behaviour of talitrids is an immediate response to environmental changes and considering behavioural adaptations as immediate responses to stressful environmental conditions, which may be dramatically increased with climate change. Starting from local comparisons, I analysed the relationships between the physical-chemical characteristics of six sandy beaches and the zonation and orientation behaviour of talitrid amphipods, ending with a comparison at a large geographical scale of two different species expressing similar behavioural adaptations in different localities.

Tese de doutoramento em Biologia (Ecologia) apresentada à Fac. de Ciências e Tecnologia da Univ. de Coimbra
Os principais objectivos subjacentes ao presente trabalho são: a investigação e identificação de espécies chave na macrofauna de praias arenosas expostas da costa ocidental Portuguesa, o estudo da bioecologia destas populações e a avaliação da possibilidade deste conhecimento bioecológico desempenhar uma função na avaliação de mudanças globais. Para que esta avaliação seja efectuada numa escala mais ampla e atingindo um maior nível de compreensão, estudos bioecológicos comparativos entre populações Atlânticas (Portugal) e Mediterrânicas oriundas da Europa (Itália) e do norte de África (Tunísia) constituem também importantes objectivos, permitindo identificar e interpretar eventuais variações observadas na bioecologia. Este trabalho será apresentado em quatro capítulos, incluindo um manuscrito submetido para publicação e três manuscritos já publicados em revistas científicas. No início é apresentada uma breve introdução às praias arenosas e à sua relevância ecológica, aos seus problemas ambientais, nomeadamente associados com actividades humanas, e à sua investigação científica nas costas Atlânticas da Europa e Mediterrânicas da Europa e norte de África. A utilização potencial de populações macrofaunais abundantes, especialmente de crustáceos das famílias Talitridae e Tylidae, como espécies chave e indicadores de mudanças ambientais é primeiramente avançada, no contexto do crescente aumento de impactos humanos negativos nestes sistemas costeiros abundantes e sensíveis. O primeiro capítulo analisa a estrutura das comunidades macrofaunais de duas praias expostas similares de Portugal, atendendo a densidades das comunidades, composição, espécies dominantes e diversidade, mas também distribuição horizontal dos organismos residentes entre as áreas supralitoral e intertidal. Foram também estudadas a influência da sazonal idade e as potenciais relações entre os dados biológicos e as variáveis ambientais. Os crustáceos Talitridae Talitrus saltator e Talorchestia brito, e Tylidae Tylos europaeus foram os animais mais abundantes nas duas praias analisadas, tendo sido identificados como espécies chave. Apesar da semelhança na exposição à ondulação de ambas as praias, as suas comunidades apresentam diferentes estruturas, nomeadamente no que diz respeito à contribuição relativa das espécies dominantes, mas também na densidade e composição das comunidades. Quanto às diferenças observadas, pensa-se que estas estarão principalmente relacionadas com diferenças no suplemento de detritos arrojados às praias (abundância e regularidade), juntamente com diferenças na granulometria do sedimento e na extensão da área intertidal. O segundo capítulo é dedicado ao estudo comparativo da dinâmica populacional, biologia e produção secundária de Talitrus saltator em praias do Atlântico e do Mediterrâneo, investigando as adaptações desta espécie à vida em locais geograficamente distintos. Este animal revelou-se como sendo semianual, com fêmeas multíparas e exibindo um ciclo de vida bivoltino em todos os locais estudados. Algumas das suas características da história de vida (e.g. longevidade, período reprodutivo) apresentaram um padrão de variação latitudinal, enquanto outras variaram de forma distinta entre populações sugerindo adaptabilidade às condições ambientais locais (e.g. densidades, proporção sexual). Os valores de produção estimados foram, em geral, similares aos observados noutros talitridae. No terceiro capítulo é apresentado um estudo comparativo da biologia, dinâmica populacional e produção secundária de Talorchestia brito entre populações Atlânticas e Mediterrânicas, estudo este que corresponde também ao primeiro estudo bioecológico completo desta espécie. Este talitridio revelou-se uma espécie semianual, com fêmeas multíparas e com um ciclo de vida bivoltino. Para a maior parte das características da história de vida (e.g. características morfométricas, longevidade, período reprodutivo) verificou-se uma variação geográfica, com a população Atlântica apresentando uma história de vida mais lenta. As proporções sexuais das populações analisadas não aparentam apresentar qualquer tipo de variação geográfica, sugerindo adaptabilidade a condições ambientais locais específicas. As estimativas de produção secundária foram semelhantes às observadas noutros Talitridae, mas menores que as observadas para as populações vizinhas de T. saltator. Porém, as proporções PI B e EI B entre ambas as espécies foram muito similares nos locais estudados. O quarto capítulo foca a biologia, dinâmica populacional e produção secundária do isópode Tylidae Tylos europaeus na costa ocidental de Portugal, produzindo o primeiro estudo bioecológico completo para esta espécie. Tylos europaeus apresentou-se como um organismo anual, com fêmeas multíparas e um ciclo de vida univoltino. A reprodução ocorreu sazonalmente, apresentando uma duração curta, e apenas uma nova coorte foi recrutada por ano. Os animais apresentaram uma longevidade longa e, relativamente à dinâmica e estrutura populacional, foram detectados de forma consistente eventos de separação de coortes (Cohort-splitting) nos machos no inicio do período reprodutivo, dotando estes indivíduos de características biológicas distintas (tamanho corporal, longevidade, contribuição para o esforço reprodutivo da população). Sugeriu-se que estes eventos constituiriam uma possível estratégia que permitiria aos machos serem bem sucedidos em termos reprodutivos, apesar da escassez de fêmeas nestas populações, o que de outra forma conduziria certamente a uma forte competição entre machos por fêmeas. A produção secundária foi relativamente baixa, especialmente quando comparada com as razões PI B dos Talitridae residentes T. saltator e T. brito, consequência da história de vida lenta deste isópode. Por fim é apresentada uma discussão geral acerca da importância dos crustáceos Talitridae e Tylidae como espécies chave em praias expostas de Portugal, e da sua relevância como indicadores do estado biológico das suas comunidades. A bioecologia local e comparativa das populações de espécies chave é discutida, revelando-se ainda uma grande plasticidade na ecologia destas populações ao longo de gradientes geográficos mas também às condições ambientais locais. A modelação da dinâmica populacional de espécies chave é discutida como uma ferramenta potencial na avaliação de mudanças ambientais em praias arenosas, apresentando-se neste contexto um exemplo concreto envolvendo uma das espécies chave estudadas no presente trabalho (Talitrus saltator). No que diz respeito aos resultados obtidos no presente estudo, o vasto conhecimento bioecológico produzido, e até mesmo o conhecimento produzido em termos de estrutura de comunidades, poderão ser considerados conhecimentos de referência no que diz respeito a praias expostas relativamente pouco perturbadas, utilizáveis no futuro como base de comparação. A grande quantidade de informação de base produzida em relação à bioecologia de espécies chave estabelece ainda um primeiro passo no sentido da construção, calibração e validação de modelos de dinâmica populacional, poderosas ferramentas na simulação e previsão de múltiplos cenários. O conhecimento produzido no presente trabalho poderá ser particularmente útil em futuras avaliações da integridade destes ecossistemas, no planeamento de cenários de gestão e em projectos de reabilitação destes ecossistemas, e torna-se especialmente relevante no contexto das rápidas mudanças globais que decorrem actualmente, a maioria das quais intimamente relacionada com as actividades humanas.
In the present work, the main underlying goals are to investigate and to identifY the existence of macrofaunal key species on exposed sandy beaches of the western coast of Portugal, to study the bio-ecology of these populations, and to evaluate the possibility of bio-ecological knowledge on key species populations presenting a role in global changes assessment. To accomplish this evaluation on a much wider and comprehensive scale, comparative bio-ecological studies between Atlantic (Portugal) and Mediterranean populations from Europe (Italy) and north Africa (Tunisia) are also important objectives that alIow the identification and interpretation of the variations observed in bio-ecology. This work wilI be presented in four specific chapters, including a manuscript submitted for publication and three manuscripts already published in scientific journals. In the beginning, a brief introduction to sandy beaches and their ecological relevance, their environmental pressures, namely associated with human activities, and their scientific research on Atlantic and Mediterranean sandy coastlines of Europe and north Africa is presented. In the scope of the increasingly human detrimental impacts on these sensitive and abundant coastal systems, the potential use of local abundant macrofaunal populations, especialIy talitrid and tylid crustaceans, as key species and indicators of environmental change is firstly approached and hypothesized. The first chapter analyses the macrofaunal community structure of two similar exposed beaches in Portugal, regarding communities' density, composition, dominant species and diversity, but also horizontal distribution of resident organisms between the supralittoral and intertidal areas. The influence of seasonality and the potential relationships between biological data and environmental variables was also studied. The crustacean talitrids Talitrus saltator and Talorchestia brito, and the tylid Tylos europaeus were the most abundant animaIs on both beaches and were identified as key species. Despite of the similarity in exposure to wave action of the beaches, their communities presented distinct structures, namely with regard to the relative contribution of the dominant species, but also in community density and composition. The differences observed are believed to be mainly explained by differences in detritus subsidies (abundance and regularity), combined with differences in sediment grain size and in the extent of the intertidal area at the study sites. The second chapter is dedicated to the comparative study of Talitrus saltator population dynamics, biology and secondary production in Atlantic and Mediterranean beaches, investigating the adaptations of this species to life in geographicalIy distinct locations. This animal was found to be semiannual, with iteroparous females, and exhibited a bivoltine life cycle at alI study sites. Some life history features of T. saltator (e.g. life span, reproductive period) presented a latitudinal cline of variation, while others varied distinctly between populations suggesting adaptability to local environmental conditions (e.g. densities, sex ratio). Production values estimated were, in general, similar to the observed for other talitrids. In the third chapter, a comparative study of the biology, dynamics and secondary production of Talorchestia brito is presented regarding Atlantic and Mediterranean populations, corresponding also to the first complete bio-ecological study on this species. This talitrid revealed itself as a semiannual species, with iteroparous females, and a bivoltine life cycle. Geographical variation was detected in most ofthe life history features (e.g. morphometrical characteristics, life span, reproductive period), with the Atlantic population presenting a slower life history. Population's sex ratios appeared not to fit in any kind of geographical variation, suggesting adaptability to specific local environmental conditions. Secondary production estimates were similar to those observed for other talitrids, but smalIer than for the neighbouring populations of T. saltator. However, population turnovers between both species were very similar at the study sites. , The forth chapter focused the biology, population dynamics and secondary production of the tylid Tylos europaeus on the western coast of Portugal, producing, for the first time, a complete and comprehensive bio-ecological study on this species. Tylos europaeus turned out to be an annual species, with iteroparous females, and a univoltine life cycle. Reproduction was seasonal and short, and only one new cohort was recruited per year. The animais were long lived and, regarding population dynamics and structure, consistent cohort-splitting events were detected in males at the beginning of the reproductive period, endowing these individuais with distinct biological characteristics (body size, lifespan, contribution to the reproductive effort). These events were suggested to be a possible strategy to cope with the highly male-biased sex ratios observed, that otherwise could lead to strong male-male competition for mates. Secondary production attributes were rather low, especially when compared with the P/ B ratios of the resident talitrids T. saltator and T. brito, a consequence of its slow life history. At last, a general discussion about the importance of talitrid and tylid crustaceans as key species on exposed sandy beaches of Portugal, and their relevance as indicators of their biological communities' state are presented. Local and comparative bio-ecology of key species populations is discussed and a strong plasticity in population ecology features over geographical gradients and also to local characteristic environmental conditions was revealed. Modelling of key species population dynamics is discussed as a potential tool for environmental change assessment in sandy beaches and a specific example, involving one of the presently studied key species is presented (Talitrus saltator). Regarding the results achieved in this study, the wide knowledge produced on key species bio-ecology, and even the community structure knowledge, might be regarded as reference knowledge on relatively undisturbed exposed sandy beaches, useful in the future as a basis for comparison. Also, the large baseline information produced regarding key species bio¬ecology establishes the first step towards the construction, calibration and validation of population dynamics models, powerful tools in simulation and prediction of multiple scenarios. The knowledge produced in the present work might be particularly useful in future ecosystem integrity assessments, planning of management scenarios and ecosystem restoration projects, and becomes especially relevant within the frame ofthe fast ongoing global changes ofthe present days, most of them closely related to human activities.

Sydney is a littoral city. Defined in equal measure by shell-grit and froth, the city is skirted by no less than a hundred lapping beaches. One or two of these have determinedly prized themselves from Sydney’s sandy pull to become internationally iconic ‘branded beaches’, due in no small part to their repeated appearance on screens of different sizes. Bondi, Manly, Coogee, Palm, Cronulla are beach names with a notoriety that now extends well beyond their shores.