Ocean Beach Research Articles

Juvenile white sharks Carcharodon carcharias use estuarine environments in south-eastern Australia

Estuarine environments are known to provide important feeding, breeding, resting and nursery areas for a range of shark species, including some which are considered dangerous to humans. Juvenile white sharks (<3 m) are known to frequent inshore environments, particularly ocean beaches, but their presence in and use of estuaries and coastal embayments is unclear. Given that estuarine environments are often surrounded by highly populated areas, understanding how white sharks use these environments will not only assist with their conservation management, but also inform public safety policies. The use of estuarine environments by acoustic-tagged white sharks was investigated from 2009 to 2015 at Port Stephens, New South Wales and Corner Inlet, Victoria, both of which adjoin known nursery areas for the species. Juvenile white sharks were detected within both estuaries, with 20 individuals recorded within the Port Stephens estuary, including four on one day. Only one tagged shark was detected within Corner Inlet; however, monitoring effort and local tagging in the area was more restricted. Detections in Port Stephens were predominantly from October to January and peaked in November. This study demonstrates that the footprint of known nursery areas for white sharks in eastern Australia should be expanded to include their adjacent estuarine environments. Consequently, there is clear potential for them to be exposed to a range of anthropogenic estuarine impacts, and that human interactions are more likely over warmer periods (summer), when human use of such waterways is more prevalent.

Morphological variations of ocean beaches of Niterói (RJ) in response to storms wave incidence

As praias da enseada de Itaipu em Niteroi (RJ) vem sendo modificadas devido a rapida urbanizacao que ocorreu apos a decada de 1970 com a construcao da ponte Rio-Niteroi. As praias de Piratininga, Sossego, Camboinhas e Itaipu sao dinâmicas e importantes para a protecao do litoral, frente as ondas de tempestades que podem alcancar 3 metros na arrebentacao. O presente estudo apresenta dados de topografia praial e de condicoes de mar obtidos durante e apos a ocorrencia de ressacas entre 2013 e 2014. Os resultados ressaltam o carater altamente dinâmico das praias oceânicas de Niteroi e a vulnerabilidade destas as grandes ondas de tempestades. O comportamento distinto dessas praias e o resultado da energia diferenciada das ondas incidentes ao longo da costa. Essas praias se estreitam rapidamente em resposta a ocorrencia de ressacas, restabelecendo-se logo a seguir quando do retorno as condicoes de tempo bom. A praia de Piratininga e a mais dinâmica, tendo variado entre 34 m e 87 m de largura no inverno. Tambem e a mais urbanizada e apresenta problemas com a destruicao de estruturas de engenharia construidas praticamente dentro do pos-praia. Foi observado uma grande mobilidade de sedimentos ao longo do arco praial em resposta a acao das correntes de deriva litorânea, no caso de Piratininga e Camboinhas, e entre a parte emersa e submersa. A B S T R A C T The beaches of the Itaipu embayment in Niteroi (Rio de Janeiro) have been modified due to rapid urbanization in the 1970s after the construction of the Rio-Niteroi bridge. The beaches of Piratininga, Sossego, Camboinhas and Itaipu are dynamic and important to protect the coast against the impact of stormy waves that can reach three meters in the breaking zone. This study presents beach topography data and sea conditions data obtained during and after storm surges between 2013 and 2014. The results highlight the highly dynamic nature of the ocean beaches of Niteroi and their vulnerability to large stormy waves. The distinct behavior of these beaches is the result of the differentiated energy of the incident waves along the coast. These beaches quickly narrow in response to storm surge and they recompose immediately with the return of good weather conditions. Piratininga beach is the most dynamic, ranging between 34 and 87 meters wide in the winter. It is also the most urbanized and it has problems with the destruction of engineering structures built practically into the backshore. These beaches exhibit high mobility of sediments longitudinally in response to action of longshore currents, especially Piratininga and Camboinhas, and between the unsubmerged and the submerged portion. Keywords: beach, coastal dynamic, geomorphology, Itaipu Embayment.

Total and extractable elemental composition of the intertidal estuarine biofilm of the Río de la Plata: Disentangling natural and anthropogenic influences

Estuarine transitional waters constitute regions affected by or at risk of anthropogenic impact due to urbanization and industrial development. The elemental composition of the intertidal biofilm sediment is an excellent marker for the detection of any impact, and may exert a bottom-up influence by natural concatenation to higher organization levels (e.g. molecules, cells, organisms, communities). The distribution pattern of elemental composition (total and bioavailable fraction) along the estuary axes was analyzed, disentangling potential shifts produced by human activities. We predict that most abundant elements in the Rio de la Plata estuary are the natural earth-crust components and that these will not show any evident gradient along the estuarine axis. Elements involved in human related processes will shape concentration gradients from the most probable source (i.e. cities) indicating estuarine pollution. The research strategy involved the sampling of intertidal biofilm along the entire estuary and the registration of environmental variables and the total and bioavailable elemental composition. Sampling sites represent pristine, agricultural, and urbanized areas along a 428-km-long coastline comprising the inner, middle and outer Río de la Plata estuarine zones and a coastal fringe of oceanic beaches of Uruguay (South America). Biofilm sediment samples were collected in Autumn 2011 and digested for total and extractable (bioavailable) elements quantification measured by ICP-OES. Mercury (Hg) sediments were digested with aqua regia and quantified by cold vapor atomic absorption (CVAAS). The most abundant elements measured were Al, Fe, and Ca in all sampling. Anthropogenic marker elements such as Hg, Cr, Pb, Zn, and Cu were found, even at potentially toxic levels, at urban beaches at the city of Montevideo. The ordination of samples highlights the distinctive characteristics of urban beaches, placed in a particular location along the first principal component. This position is mainly driven by human impact marker metals and C/N ratios. The results highlight the value of bioavailable elemental composition analyses of benthic biofilm as a tool for detecting shifts in estuarine systems.

Memorials for lost environments: Participatory practice and minimal ethicss

Participatory performance can respond to differing temporal and spatial perspectives of Anthropogenic climate change as an embodied practice of ‘minimal ethics’ (Zylinska, 2014). By taking up the theme of ‘survival’, performatively I explore questions of survival in relation to the individual and larger society through the survival of being-with as a ‘new’ modality for living on this earth and beyond our selves (Heidegger, 1996). I draw the Poetics of Failure (Bailes, 2011) and Schneider (2011) in the creation of performance rituals that activate presence through absence. This paper discusses the performance walk, Be for barefoot—A survival walk on Ocean Beach in Dunedin, Otago, as a mobile community enacting a memorial emerging from the remains of personal and environmental tragedy. The walking and sharing of stories of survival contributes to rituals of wellbeing as a way to create hope in the face of environmental uncertainty.

Behavioural responses of talitrid amphipods to recreational pressures on oceanic tropical beaches with contrasting extension

Ocean sandy beaches are prime sites for human recreation. The integrity of these ecosystems may suffer greatly from tourism-related pressures. Behavioural adaptations of fauna are key traits as responses to environmental pressures and short time changes. In particular, orientation performance of talitrid amphipods to recover the optimal zone on the beach has been proposed as bioindicator of shoreline stability, mainly related to sedimentary dynamics and geomorphological changes. The question focused here was whether recreational activities and urbanisation may influence orientation performance of talitrids on oceanic tropical beaches with contrasting extension (beach length).Field orientation experiments were performed during Spring 2014 testing populations of the talitrid Atlantorchestoidea brasiliensis on four tropical beaches at Rio de Janeiro (Brazil), selected according to their human access (two with and two without public access) and length (two pocket and two extended beaches). The influence of landscape cues on the orientation of talitrids was experimentally tested in two etho-assay conditions: with and without the landscape vision. Talitrids used landscape cues and sun compass to orient seawards and the highest precision of orientation was recorded in the pocket beach without human access. A more scattered response was observed in the urbanised pocket beach under conditions of screened landscape and when the sun was veiled or covered by clouds, showing the importance of the local landscape features in these conditions. The populations from the extended beaches showed a similar and more scattered orientation, which may be interpreted as behavioural plasticity to cope with beach natural changes, disregarding human pressure on the beaches. The behavioural performances of talitrids on the four tropical beaches varied according to different human pressure conditions and beach extension, confirming the reliability of the use of talitrid orientation as bioindicator of beach changeability.

The Early Shorebird Will Catch Fewer Invertebrates on Trampled Sandy Beaches.

Many species of birds breeding on ocean beaches and in coastal dunes are of global conservation concern. Most of these species rely on invertebrates (e.g. insects, small crustaceans) as an irreplaceable food source, foraging primarily around the strandline on the upper beach near the dunes. Sandy beaches are also prime sites for human recreation, which impacts these food resources via negative trampling effects. We quantified acute trampling impacts on assemblages of upper shore invertebrates in a controlled experiment over a range of foot traffic intensities (up to 56 steps per square metre) on a temperate beach in Victoria, Australia. Trampling significantly altered assemblage structure (species composition and density) and was correlated with significant declines in invertebrate abundance and species richness. Trampling effects were strongest for rare species. In heavily trafficked plots the abundance of sand hoppers (Amphipoda), a principal prey item of threatened Hooded Plovers breeding on this beach, was halved. In contrast to the consistently strong effects of trampling, natural habitat attributes (e.g. sediment grain size, compactness) were much less influential predictors. If acute suppression of invertebrates caused by trampling, as demonstrated here, is more widespread on beaches it may constitute a significant threat to endangered vertebrates reliant on these invertebrates. This calls for a re-thinking of conservation actions by considering active management of food resources, possibly through enhancement of wrack or direct augmentation of prey items to breeding territories.

Natural bitumen stranding on the ocean beaches of Southern Australia: a historical and geospatial review

ABSTRACTThe stranding of bitumen on ocean beaches in South Australia and western Victoria has been known for at least 170 years. In this review, we define what is meant by “coastal bitumen”, illustrate its different varieties, and present the results of the first quantitative geospatial survey of its occurrence in South Australia. We then summarise the distinguishing molecular and isotopic characteristics of six families of these “ocean wanderer” bitumens, as pointers to their likely provenance.A bimonthly survey of six South Australian beaches conducted during 1991–1992 identified three categories of stranded petroleum: waxy bitumen, asphaltite and oil slicks. Each is physically and chemically distinct and bears no resemblance to any crude oil so far discovered in Australia’s sedimentary basins. The maximum waxy bitumen loading of the beaches visited was 2 kg per 100 m. Accounting for 90% of the strandings, the waxy bitumens originate from oil seeps within the Indonesian Archipelago and are transported into southern Australian waters as flotsam by a complex system of surface ocean currents. The less common asphaltite is now understood to be a product of low-intensity seepage from tar mats exposed by the incision of submarine canyons into Australia’s southern continental slope. The oil slicks represent occasional spillage from local maritime traffic.The stranding of petroleum along Australia’s southern coastline therefore can be attributed to both natural and anthropogenic causes. The recent commencement of a new phase of oil and gas exploration in the Great Australian Bight highlights the need to characterise and quantify these inputs to the hydrocarbon loading of the adjacent ocean beaches.

Remote sensing of nearshore wave interference

AbstractWave focusing of energetic swell fields can result in small‐scale variations associated with coherent interference that can be important for nearshore circulation and beach dynamics. However, coherent interference is difficult to measure with conventional in situ instruments and is not accounted for in operational wave models. As a result, such effects are generally ignored. In this work, we analyze X‐band radar observations collected at Ocean Beach, San Francisco using a Wigner‐Ville or coupled‐mode spectrum, to show how long‐dwell remote sensing technology allows us to identify coherent wave interference. Our analysis demonstrates that during energetic swell events, the nearshore wave field consists of two noncollinear, but coherent, swell patterns that originate from the same offshore source but are directionally separated due to refraction over the San Francisco Bar. The length scale of the associated alongshore wave height variability (200 m) is consistent with the wavenumber separation obtained from the coupled mode analysis. This confirms that the small‐scale variability is primarily due to coherent interference. In addition, our analysis shows that the shoreline exhibits a strong localized response near the radar site on the 200 m scale, which suggests that coherent interference effects can affect wave‐driven nearshore transport processes and localized erosion.

A morphological modeling study to compare different methods of wave climate schematization and evaluate strategies to reduce erosion losses from a beach nourishment project

Beach nourishment on open ocean beaches not bounded by headlands or other structures suffers from high rates of lateral losses of fill volume as the nourished shoreline equilibrates with its surroundings. Estimates of lateral losses are essential for beach nourishment design, these predictions have been made in the last decade utilizing empirical formulations, one line models or lately, process-based coastal morphology models. Coastal morphology models are, however, complex and computationally intensive and in order to maintain a balance between model complexities, computational effort and processing capacity, schematization of model input (input reduction) is necessary. This paper is divided into two main sections. In the first section techniques of wave input reduction for morphological models are evaluated with focus on open ocean wave-dominated coasts. Subsequently, the optimized morphological model is applied to evaluate coastal engineering interventions aimed at reducing volume losses from the Delray Beach nourishment project. Wave input reduction is defined here as the process of reducing the full wave climate of a given coastal region to a set of representative wave-wind conditions, ‘running’ a model with these representative wave conditions in sequence for a smaller time period (i.e. a few tide cycles) and multiplying its effect on the morphology by a Morfac value, that is related to the frequency of occurrence of that wave condition in nature, or its weight in the overall wave climate. Five different techniques of wave input reduction were tested. Of all the methods of wave climate schematization tested the methods defined as ‘Energy Flux Method’ and ‘Opti Method’ showed best results in terms of representing accurately the sediment transport patterns of the study area. The tests conducted indicate that a number around 12 representative wave cases was enough to represent an annual wave climate compared to a very detailed wave climate used as benchmark. The optimized model was used to evaluate alternative engineering solutions to reduce volumetric losses from the beach nourishment project. Engineering solutions evaluated included a construction of a breakwater field, backfilling all dredge pits located offshore of the project site, construction of a groin field at the downdrift end of the project, and backfilling the deepest dredge pit. These engineering interventions caused a reduction in beach volume losses within the project limits with varying levels of effect on the downdrift beaches. Reduction of the volume loss from the project site is technically feasible and may be economically feasible pending further economic feasibility evaluation.

Impacts of wave and tidal forcing on 3D nearshore processes on natural beaches. Part II: Sediment transport

This is the second of two papers on the 3D numerical modeling of nearshore hydro- and morphodynamics. In Part I, the focus was on surf and swash zone hydrodynamics in the cross-shore and longshore directions. Here, we consider nearshore processes with an emphasis on the effects of oceanic forcing and beach characteristics on sediment transport in the cross- and longshore directions, as well as on foreshore bathymetry changes. The Delft3D and XBeach models were used with four turbulence closures (viz., k-e, k-L, ATM and H-LES) to solve the 3D Navier-Stokes equations for incompressible flow as well as the beach morphology. The sediment transport module simulates both bed load and suspended load transport of non-cohesive sediments. Twenty sets of numerical experiments combining nine control parameters under a range of bed characteristics and incident wave and tidal conditions were simulated. For each case, the general morphological response in shore-normal and shore-parallel directions was presented. Numerical results showed that the k-e and H-LES closure models yield similar results that are in better agreement with existing morphodynamic observations than the results of the other turbulence models. The simulations showed that wave forcing drives a sediment circulation pattern that results in bar and berm formation. However, together with wave forcing, tides modulate the predicted nearshore sediment dynamics. The combination of tides and wave action has a notable effect on longshore suspended sediment transport fluxes, relative to wave action alone. The model’s ability to predict sediment transport under propagation of obliquely incident wave conditions underscores its potential for understanding the evolution of beach morphology at field scale. For example, the results of the model confirmed that the wave characteristics have a considerable effect on the cumulative erosion/deposition, cross-shore distribution of longshore sediment transport and transport rate across and along the beach face. In addition, for the same type of oceanic forcing, the beach morphology exhibits different erosive characteristics depending on grain size (e.g., foreshore profile evolution is erosive or accretive on fine or coarse sand beaches, respectively). Decreasing wave height increases the proportion of onshore to offshore fluxes, almost reaching a neutral net balance.

Development of Beach Health Index for the Gold Coast, Australia

ABSTRACT Todd D.J. and Bowra, K., 2016. Development of beach health index for the Gold Coast, Australia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 710–714. Coconut Creek (Florida), ISSN 0749-0208. The City of Gold Coast Council “Ocean Beaches Strategy 2013–2023” included the preparation of an annual Beach Health Report as a key action for measuring whether the city's beach were clean and healthy. As a result, the Griffith Centre for Coastal Management and City of Gold Coast have been investigating what are the most appropriate indicators and reporting systems for beach health that will provide an objective rating of the overall quality of Gold Coast beaches, both in the present and in the future. An initial literature review concluded that the most suitable beach health rating system was a system based on the framework of the existing “Ocean...

Assessing the spatial compatibility of recreational activities with beach vegetation and wrack in New Jersey: Prospects for compromise management

This study examines the prospects for compromise management to support greater natural resources on recreational beaches by analyzing the spatial dimensions of key natural resource indicators (beach vegetation and wrack) with peak recreational uses in New Jersey, one of the most intensively developed shorelines in North America. The spatial distribution of pedestrian and vehicular recreational uses was measured on 60 transects in heavily-populated beaches during the peak times and days of use during the summer tourist season, and compared to that of vegetation and wrack on 72 transects in nearby protected natural areas. The frequency, density, and % use were calculated for each 10% increment of linear beach surface, and the impacts of protecting different amounts of upper beach areas were calculated in terms of the % vegetation, wrack and recreational use that would be supported in each case. Vegetation was highly concentrated in landward portions of the beach surface, and pedestrian and parked recreational vehicles in the seaward areas, suggesting high compatibility of these natural resources with recreational use. Lower compatibility was found for existing patterns of wrack and vehicle driving, which were more widely distributed across the beach surface. Based on the distributions of these variables, protecting the upper 50% of the beach would support >80% of vegetation, pedestrian and parked vehicular uses, and 42–52% of driving uses and wrack, respectively. Protecting the upper 25% of the beach would support >95% of all recreational uses, 52% of vegetation, and 24% of wrack. Given the current level of impacts to vegetation and wrack on recreational beaches, major gains in these and other natural resources can therefore be made across the shoreline without substantial impacts to existing pedestrian or vehicular recreational uses. Greater ecological benefits and ecosystem services may be obtained by applying these types of compromise management solutions to recreational ocean beaches in the future.

Human threats to sandy beaches: A meta-analysis of ghost crabs illustrates global anthropogenic impacts.

Beach and coastal dune systems are increasingly subjected to a broad range of anthropogenic pressures that on many shorelines require significant conservation and mitigation interventions. But these interventions require reliable data on the severity and frequency of adverse ecological impacts. Such evidence is often obtained by measuring the response of ‘indicator species’.Ghost crabs are the largest invertebrates inhabiting tropical and subtropical sandy shores and are frequently used to assess human impacts on ocean beaches. Here we present the first global meta-analysis of these impacts, and analyse the design properties and metrics of studies using ghost-crabs in their assessment. This was complemented by a gap analysis to identify thematic areas of anthropogenic pressures on sandy beach ecosystems that are under-represented in the published literature.Our meta-analysis demonstrates a broad geographic reach, encompassing studies on shores of the Pacific, Indian, and Atlantic Oceans, as well as the South China Sea. It also reveals what are, arguably, two major limitations: i) the near-universal use of proxies (i.e. burrow counts to estimate abundance) at the cost of directly measuring biological traits and bio-markers in the organism itself; and ii) descriptive or correlative study designs that rarely extend beyond a simple ‘compare and contrast approach’, and hence fail to identify the mechanistic cause(s) of observed contrasts.Evidence for a historically narrow range of assessed pressures (i.e., chiefly urbanisation, vehicles, beach nourishment, and recreation) is juxtaposed with rich opportunities for the broader integration of ghost crabs as a model taxon in studies of disturbance and impact assessments on ocean beaches. Tangible advances will most likely occur where ghost crabs provide foci for experiments that test specific hypotheses associated with effects of chemical, light and acoustic pollution, as well as the consequences of climate change (e.g. species range shifts).

Functional replacement across species pools of vertebrate scavengers separated at a continental scale maintains an ecosystem function

Summary The composition of species pools can vary in space and time. While many studies are focused on understanding which factors influence the make‐up of species pools, the question to which degree biogeographic variation in species composition propagates to biogeographic variation in ecological function is rarely examined. If different local species assemblages operate in ways that maintain specific ecological processes across continents, they can be regarded as functionally equivalent. Alternatively, variation in species assemblages might result in the loss of ecological function if different species fulfil different functions, and thereby fail to maintain the ecological process. Here, we test whether ecological function is affected by differences in the composition of species pools across a continental scale, comparing a tropical with a temperate pool. The model systems are assemblages of vertebrates foraging on ocean beaches, and the ecological function of interest is the consumption of wave‐cast carrion, a pivotal process in sandy shore ecosystems. We placed fish carcasses (n = 179) at the beach–dune interface, monitored by motion‐triggered cameras to record scavengers and quantify the detection and removal of carrion. Scavenging function was measured on sandy beaches in two distinct biogeographic regions of Australia: tropical north Queensland and temperate Victoria. The composition of scavenging assemblages on sandy beaches varied significantly across the study domain. Raptors dominated in the tropics, while invasive red foxes were prominent in temperate assemblages. Notwithstanding the significant biogeographic change in species composition, ecological function – as indexed by carcass detection and removal – was maintained, suggesting strong functional replacement at the continental scale. Species pools of vertebrate scavengers that are assembled from taxonomically distinct groups (birds vs. mammals) and located in distinct climatic regions (temperate vs. tropical) can maintain an ecological process via replacement of species with comparable functional traits.

Edging along a Warming Coast: A Range Extension for a Common Sandy Beach Crab.

Determining the position of range edges is the first step in developing an understanding of the ecological and evolutionary dynamics in play as species’ ranges shift in response to climate change. Here, we study the leading (poleward) range edge of Ocypode cordimanus, a ghost crab that is common along the central to northern east coast of Australia. Our study establishes the poleward range edge of adults of this species to be at Merimbula (36.90°S, 149.93°E), 270 km (along the coast) south of the previous southernmost museum record. We also establish that dispersal of pelagic larvae results in recruitment to beaches 248 km (along the coast; 0.9° of latitude) beyond the adult range edge we have documented here. Although we cannot conclusively demonstrate that the leading range edge for this species has moved polewards in response to climate change, this range edge does fall within a “hotspot” of ocean warming, where surface isotherms are moving southwards along the coast at 20–50 km.decade-1; coastal air temperatures in the region are also warming. If these patterns persist, future range extensions could be anticipated. On the basis of their ecology, allied with their occupancy of ocean beaches, which are home to taxa that are particularly amenable to climate-change studies, we propose that ghost crabs like O. cordimanus represent ideal model organisms with which to study ecological and evolutionary processes associated with climate change. The fact that “hotspots” of ocean warming on four other continents correspond with poleward range edges of ghost crab species suggests that results of hypothesis tests could be generalized, yielding excellent opportunities to rapidly progress knowledge in this field.

Invasive carnivores alter ecological function and enhance complementarity in scavenger assemblages on ocean beaches.

Species composition is expected to alter ecological function in assemblages if species traits differ strongly. Such effects are often large and persistent for nonnative carnivores invading islands. Alternatively, high similarity in traits within assemblages creates a degree of functional redundancy in ecosystems. Here we tested whether species turnover results in functional ecological equivalence or complementarity, and whether invasive carnivores on islands significantly alter such ecological function. The model system consisted of vertebrate scavengers (dominated by raptors) foraging on animal carcasses on ocean beaches on two Australian islands, one with and one without invasive red foxes (Vulpes vulpes). Partitioning of scavenging events among species, carcass removal rates, and detection speeds were quantified using camera traps baited with fish carcasses at the dune-beach interface. Complete segregation of temporal foraging niches between mammals (nocturnal) and birds (diurnal) reflects complementarity in carrion utilization. Conversely, functional redundancy exists within the bird guild where several species of raptors dominate carrion removal in a broadly similar way. As predicted, effects of red foxes were large. They substantially changed the nature and rate of the scavenging process in the system: (1) foxes consumed over half (55%) of all carrion available at night, compared with negligible mammalian foraging at night on the fox-free island, and (2) significant shifts in the composition of the scavenger assemblages consuming beach-cast carrion are the consequence of fox invasion at one island. Arguably, in the absence of other mammalian apex predators, the addition of red foxes creates a new dimension of functional complementarity in beach food webs. However, this functional complementarity added by foxes is neither benign nor neutral, as marine carrion subsidies to coastal red fox populations are likely to facilitate their persistence as exotic carnivores.

Tide, time and space: Scales of variation and influences on structuring and sampling beach clams

Scales of spatio-temporal variability in the densities and sizes of organisms need to be quantified so that the relative importance of different ecological processes that structure assemblages can be determined and future sampling strategies optimized. This study examined variability in the densities and size compositions of the beach clam, Donax deltoides, across tide stages and various hierarchical scales of time (day, week, month, season) and space (patch, area, beach). Densities of clams in the swash zone were most often least at high tide, which may be a consequence of their restricted shoreward movements and upper beach distributions. Regardless, the size compositions of sampled clams were the same across all tide stages. Future quantitative population sampling could be done across a six-hour window around low tide, providing ample time to access and sequentially sample many locations along a beach. The components of variation in densities of clams were in all but a couple of cases, greatest at the smallest temporal and spatial scales examined; among days and among replicate samples within a patch. Variation in size compositions was also greatest at the smallest spatial scale examined (among patches), but this was not the case for time. Size compositions were relatively stable across days and the influences of other temporal scales were inconsistent, suggesting that ecological processes influencing size compositions operate at different scales to those influencing densities. Nevertheless, the general predominance of small-scale variation was probably a consequence of fine-tuned, local-scale responses of clams to the variable and dynamic physical and biogenic features of the swash zone habitat. These results concur with studies in other habitats that show small-scale temporal and spatial variability is a dominant feature of aquatic benthic organisms and challenges the paradigm that ocean beach ecology is primarily driven by large-scale hydrodynamic forces. Small-scale patchiness of clams in time and space needs to be taken into consideration in future sampling strategies for population and impact assessments. Moreover, the ecological processes that drive small-scale temporal and spatial structuring of organisms on ocean beaches require greater investigation.

Trophic connectivity and basal food sources sustaining tropical aquatic consumers along a mangrove to ocean gradient

Variations in the relative importance of autotrophic sources to aquatic consumers along environmental gradients and the trophic role of mangrove-derived detritus to marine coastal food webs are still poorly investigated in tropical systems. In this study, we employed stable isotope analyses to investigate the relative importance of basal food sources to macroconsumers (decapod crustaceans and fishes) in a tropical estuary along an environmental gradient extending from the mangroves to the ocean. Additionally, we evaluated the ‘outwelling hypothesis’, which hypothesizes that mangrove-derived detritus exported to the adjacent marine area is a food source for marine macroconsumers at open and reef-protected sandy beaches. Primary producers and macroconsumers (62 and 214 samples, respectively) were collected at five locations across the main longitudinal axis of the Mamanguape estuary, a tropical Southwestern Atlantic estuary. There were marked shifts in carbon and nitrogen isotope values for both food sources and consumers along the estuarine-marine gradient, and the mixing model results revealed similar patterns of assimilation of basal food sources by decapod crustaceans and fishes. In the inner section of the estuary, consumers tended to assimilated nutrients derived mainly from mangrove and macroalgae, whereas nearer the mouth of the estuary and in the adjacent marine area they assimilated nutrients derived mainly from macroalgae, seagrass and organic matter in the sediment (SOM). These findings support the hypothesis that the relative importance of basal food sources to macroconsumers in this tropical estuarine system reflects the dominant autochthonous primary production at each location. In contrast, our results did not support the outwelling hypothesis that mangrove-originated detritus, in the form of senescent mangrove leaves, makes a significant contribution as a primary source of carbon to high-order consumers inhabiting adjacent ocean sandy beaches.

Coastal Vertebrate Exposure to Predicted Habitat Changes Due to Sea Level Rise

Sea level rise (SLR) may degrade habitat for coastal vertebrates in the Southeastern United States, but it is unclear which groups or species will be most exposed to habitat changes. We assessed 28 coastal Georgia vertebrate species for their exposure to potential habitat changes due to SLR using output from the Sea Level Affecting Marshes Model and information on the species' fundamental niches. We assessed forecasted habitat change up to the year 2100 using three structural habitat metrics: total area, patch size, and habitat permanence. Almost all of the species (n=24) experienced negative habitat changes due to SLR as measured by at least one of the metrics. Salt marsh and ocean beach habitats experienced the most change (out of 16 categorical land cover types) across the three metrics and species that used salt marsh extensively (rails and marsh sparrows) were ranked highest for exposure to habitat changes. Species that nested on ocean beaches (Diamondback Terrapins, shorebirds, and terns) were also ranked highly, but their use of other foraging habitats reduced their overall exposure. Future studies on potential effects of SLR on vertebrates in southeastern coastal ecosystems should focus on the relative importance of different habitat types to these species' foraging and nesting requirements. Our straightforward prioritization approach is applicable to other coastal systems and can provide insight to managers on which species to focus resources, what components of their habitats need to be protected, and which locations in the study area will provide habitat refuges in the face of SLR.

Shorebird Seasonal Abundance and Habitat-Use Patterns in Punta Rasa, Samborombón Bay, Argentina

Shorebird assemblage composition and habitat-use patterns were characterized at Punta Rasa during the austral summer, autumn and winter. Compared to other sites within the region, this area showed high species richness, reflected by a total of 22 species recorded within a relatively short time frame. Differences in assemblage structure were driven by the use of estuarine mudflats and oceanic sandy beaches as feeding habitats. During low tide, more species used estuarine environments, achieving the highest total densities. Abundance patterns and assemblage composition also changed seasonally. Maximum total abundance occurred during the austral summer, and minimum total abundance during the austral winter. During the austral summer, the assemblage was dominated by Nearctic migrants such as American Golden-Plover (Pluvialis dominica), Hudsonian Godwit (Limosa haemastica) and White-rumped Sandpiper (Calidris fuscicollis). In addition, Two-banded Plover (Charadrius falklandicus) and American Oystercatcher (Haematopus palliatus) were abundant during the austral autumn. The Red Knot (Calidris canutus), a shorebird that dominated the austral autumn assemblage 25 years ago, was recorded in relatively small numbers during this study, probably reflecting the global population trend of a subspecies of the Red Knot (C. c. rufa) in the past two decades. During the austral winter, resident birds largely dominated the assemblage. However, it is noteworthy that some individuals of nine Nearctic migrant species remained in the area. In the case of the endangered Red Knot, Punta Rasa is, along with Lagoa do Peixe in Brazil, one of the sites in South America with the highest known abundances during the austral winter.