Disturbed Beaches Research Articles

Ecological patterns of intertidal macrofauna across an anthropic gradient on tropical Gulf of Mexico sandy beaches: Insights for assessment

In the context of sandy coastlines under increasing coastal development and squeeze, coupled with the ongoing loss of global diversity, it is crucial to understand the ecological patterns of benthic macrofauna, which plays a key role in the trophic and biogeochemical functional connectivity between land and sea. Here, we assessed differences in the spatiotemporal patterns of macrofauna diversity and production in exposed sandy beaches of the southwestern Gulf of Mexico across a use and modification gradient and its utility as indicators of impacts. We also estimated the sampling effort for a representative species inventory, considering three tidal zones, and longitudinal spatial scales in four beaches twice a year, and locally after an event of great tourist incidence. The traditional diversity indices could not conclusively detect the stress gradient of the macrofauna in these systems. The abundance pattern of macrofauna species in the upper intertidal zone and the greater secondary production at the lower zone of the unmodified beaches could be useful as indicators of ecological integrity in natural beaches with similar morphodynamic conditions. On the contrary, the most disturbed beach exhibited greater instability in terms of its macrofauna temporal variation in the lower zone. We verified that the ecological integrity approach comprising both natural and anthropogenic factors and multiple stressors is a useful tool showing precisely how beach-intensive use and modification induce instability and less resilience of its macrofauna, reflected in the species' distribution by tidal zones, and the secondary production patterns. We also provide the first estimate of the optimal sampling effort required to get a representative inventory of the benthic intertidal macrofauna in sandy beaches of the Western Gulf of Mexico within a gradient.

Fiddler crabs from highly disturbed beaches are more sensitive to human presence.

The presence of humans frequently modifies the behavior of animals, particularly their foraging patterns, compromising energetic demands. The fiddler crab Leptuca leptodactyla inhabits mangroves with high degrees of anthropogenic influence. Thus, we tested if populations living in highly anthropized mangroves respond differently from those living in more protected areas. We predict that individuals from touristy areas will be more tolerant to humans and will resume their activities sooner after disturbance. To do so, we conducted an experiment that consisted in the approach of an observer to the burrows, recording the response of individuals to the stimuli. The experiment took place in July 2022, in Ubatuba, São Paulo, Brazil. We analysed the duration and latency of various behaviors of a total of 80 adult males from two populations (high and low anthropogenic influence). Contrary to our predictions, individuals from the anthropized population were less tolerant, spending more time inside their burrows and taking longer to resume their activities. Therefore, fiddler crabs were not habituated to human presence. These results help us understand the learning process in invertebrates and their ability to select stimuli, contributing to understanding the impacts of human-wildlife interactions.

Characterization of Intertidal Macrofaunal Communities of Two Sandy Beaches under Different Anthropogenic Pressures

The macrofauna in the intertidal zone of sandy beaches provides the trophic connectivity between land and sea, by linking microbiome, meiofauna, and megafauna, representing a food source for several terrestrial animals, including shorebirds and mammals. However, the macrozoobenthos in urbanised beaches is subjected to intense disturbances, such as breakwater barriers and tourism, which limit or impede the energy transfer from the marine to the terrestrial habitats. Because the information about diversity and abundance of the macrozoobenthos of the intertidal zone on the Mediterranean sandy coasts is scant, the main objective of this study is to increase the knowledge on the macrofauna living in this habitat and to identify taxa sensitive to cumulative human-induced stresses. To achieve this purpose, the structure and dynamics of macrozoobenthic communities from (1) a highly frequented beach characterized by breakwater barriers and (2) a marine protected area (MPA) in the Adriatic Sea were compared. The hypotheses that macrofauna composition and abundance changed in the two sites and over time were tested. Results highlighted that the macrozoobenthos in the MPA is mainly dominated by juvenile bivalves, which peaked from autumn to winter, and to a lesser extent by ostracods and mysids. Conversely, ostracods and the bivalve Lentidium mediterraneum (O. G. Costa, 1830) are particularly abundant in the highly disturbed beach, while the gastropod Tritia neritea (Linnaeus, 1758) increased only during summer. A possible combined effect of breakwater barriers and intense trampling has been theorized to explain the main differences between the two sites especially in the summer.

Occurrence and Behaviour of Shorebirds Depend on Food Availability and Distance of Beaches from Urban Settlements

Coastal ecosystems provide important feeding opportunities for shorebirds, depending on their prey availability, hydrodynamic conditions and human pressure. We aimed to evaluate short-term responses (occurrence and minimum approach distance) of shorebirds to urbanization and natural drivers on an extensive beach arc adjacent to the largest hypersaline coastal lagoon of South America. The presence of the migrant Sanderling Calidris alba and resident Collared Plover Charadrius collaris was geo-coordinated and for each record and an equivalent number of random points we measured the distance from urban settlements, swash width and invertebrate abundance (food availability) in a snapshot sampling. The distance at which each shorebird flock escaped from humans was determined (minimum approach distance). The occurrence of shorebirds was predicted by food availability, and higher crustacean density was found in areas of shorebird occurrence (37 ± 19 individuals/m2) compared to random points (10 ± 10 individuals/m2). This result highlights the importance of the beach as a feeding area and the need for conservation of shorebirds' prey. The resident Collared Plover delayed their escape from humans in areas closer to urban areas, suggesting a higher tolerance to humans on disturbed beaches, where they can prioritize the food intake rather than vigilance. The larger flocks let the researcher get closer, corroborating the risk-dilution theory stating that flocking behaviour during foraging provides protection of birds from predators. In conclusion, our results showed that monitoring of sandy beaches based on shorebirds' presence and behaviour can be a reliable tool, especially close to coastal lagoons that constitute foraging sites for these charismatic species.

Four‐legged foes: dogs disturb nesting plovers more than people do on tourist beaches

Recreational activities in nature have increased considerably in recent decades. Human disturbance may trigger similar trade‐offs in birds that the natural risk of predation generates on productivity through parental investment decisions. To estimate how the impact of human presence affects breeding birds on Mediterranean beaches, the behaviour of incubating Kentish Plovers Charadrius alexandrinus was studied in relation to the approach of people, vehicles and dogs. Observational data were collected and control experiments were performed with a standardized stimulus. The response variability of birds in the decision to flush from the nest was studied depending on the type of beach user, the location of the disturbance event and thermal stress. Walkers, when accompanied by dogs, flushed plovers 93.8% of the time when walking through dunes and 80.0% of the time when walking on paths, whereas pedestrians alone flushed plovers 47.6% of the time when in dunes and only 12.9% of the time when on paths. Lone dogs triggered a flushing response 100% of the time when they roamed the dunes and 50% on the shore. The number of users in each disturbance event did not affect the flushing behaviour. Nest return times were shorter on disturbed beaches, suggesting habituation to the human disturbance stimulus. The ambient temperature for the nests in which plovers flushed was lower and nest return time decreased proportionally with ambient temperature, both suggesting that habituation to the human disturbance stimulus encourages relaxation of the trade‐off between escape behaviour to avoid predation risk and the effects of thermal stress on unattended eggs. Females flushed more frequently (57.1%) than males (32.0%), suggesting that they may perceive risk differently. Establishing buffers between nesting areas and people may help birds habituate to the predictable and non‐lethal stimulus of human presence, facilitating coexistence between conservation and recreation.

Insights Into Aboriginal Australian Mortuary Practices: Perspectives From Ancient DNA

Paleogenetics is a relatively new and promising field that has the potential to provide new information about past Indigenous social systems, including insights into the complexity of burial practices. We present results of the first ancient DNA (aDNA) investigation into traditional mortuary practices among Australian Aboriginal people with a focus on North-East Australia. We recovered mitochondrial and Y chromosome sequences from five ancestral Aboriginal Australian remains that were excavated from the Flinders Island group in Cape York, Queensland. Two of these individuals were sampled from disturbed beach burials, while the other three were from bundle burials located in rock shelters. Genomic analyses showed that individuals from all three rock shelter burials and one of the two beach burials had a close genealogical relationship to contemporary individuals from communities from Cape York. In contrast the remaining male individual, found buried on the beach, had a mitochondrial DNA sequence that suggested that he was not from this location but that he was closely related to people from central Queensland or New South Wales. In addition, this individual was associated with a distinctive burial practice to the other four people. It has been suggested that traditionally non-locals or lower status individuals were buried on beaches. Our findings suggest that theories put forward about beach burials being non-local, or less esteemed members of the community, can potentially be resolved through analyses of uniparental genomic data. Generally, these results support the suggestion often derived from ethnohistoric accounts that inequality in Indigenous Australian mortuary practices might be based on the status, sex, and/or age of individuals and may instead relate to place of geographic origin. There is, however, some departure from the traditional ethnohistoric account in that complex mortuary internments were also offered to female individuals of the community, with genomic analyses helping to confirm that the gender of one of the rockshelter internments was that of a young female.

Co-occurring factors affecting ghost crab density at four sandy beaches in the Mexican Caribbean

Human pressure can cause a decrease in the abundance of beach macrofauna, especially supralittoral crustaceans. In studying the life history traits of supralittoral crustaceans, human impact and beach features (e.g. beach slope, grain size, swash width) are often considered separately. Ghost crabs are widely accepted as ecological indicators of beach quality and condition since their abundance decreases at disturbed beaches; moreover, ghost crabs can respond to natural drivers. This study aims to determine factors affecting the density of the ghost crab Ocypode quadrata in the Mexican Caribbean. We studied the spatiotemporal variation of the density of ghost crabs at two urbanized and two reference beaches by counting crab burrows on all beaches during six sampling periods. Our results indicate that physical features of the beach are significantly correlated with burrow density, and burrow density varies substantially between urbanized and reference beaches. The greater variation of burrow density accounted for beach disturbance, followed by beach morphodynamic features. Based on these results, our study confirms that the ghost crab is a relevant biological indicator species and is useful for guiding beach management criteria in the Mexican Caribbean. Our findings demonstrate that temporal replications must be included when using ghost crabs as ecological indicators.

Comparing the diversity of interstitial crustaceans at natural and artificial/degraded beaches in Okinawa

Okinawa, a subtropical island in southern Japan, is well-known for its unique biodiversity, but relatively few studies have been conducted to monitor the effects of anthropogenic disturbances on marine ecosystems. Recent work has shown that disturbed artificial beaches have lower numbers and diversity of interstitial amphipods and isopods when compared to natural beaches. In this study, we collected interstitial crustaceans from six different sandy beaches around Okinawa-jima Island in May 2018, including heavily disturbed beaches near reclaimed land, artificial tourist beaches (=disturbed environment), and undisturbed, natural beaches far away from anthropogenic disturbances (=control) in order to more fully explore the range of diversity across a full spectrum of environments. We additionally utilized 18S ribosomal DNA barcodes and Automatic Barcode Gap Discovery (ABGD) to identify specimens to operational taxonomic units (OTUs). DNA barcodes showed 34 OTUs, and the method was more efficiently able to identify to the species-level, while morphological identifications often were only efficient to the genus or family level. In comparison with former data from 2015 in Okinawa, the overall numbers and diversity of amphipods and isopods were lower. Similar to previous results, natural beaches showed higher diversity in comparison with artificial/disturbed beaches. These results suggest that disturbances cause reductions in interstitial crustacean diversity.

Investigating the effects of disturbed beaches on crustacean biota in Okinawa, Japan

Subtropical Okinawa Island is known for its high marine biodiversity, yet relatively little work has been performed on examining the impacts of coastal development on its marine ecosystems. In this study, we examined three sandy disturbed beaches (including two artificial beaches) on three different sides of the island (artificial Ginowan Tropical Beach on the west coast, artificial Azama San-san Beach on the east coast, public Odo John Man Beach on the south coast) to investigate if differences exist in the environment and crustacean biota between paired disturbed and natural beaches. We conducted seasonal surveys (n=4 surveys) by placing quadrats at three paired locations (artificial/disturbed and natural beaches at each location, to collect and record the diversity of infaunal crustacean (isopods and amphipods) taxa. Amphipods and isopods are basal parts of the food chain and therefore many marine creatures’ diets contain them directly or indirectly, and they have been used in many studies as bioindicators. As well, environmental parameters including sand grain size, water temperature, and seawater quality (salinity, dissolved oxygen content, particulate organic matter, turbidity, conductivity, pH, phosphate, nitrite, nitrate, ammonium levels) were obtained from each site during each survey. The results showed that while water nutrients, sand composition, and water quality were very similar between paired disturbed and natural beaches, disturbed beaches had significantly less biodiversity. These results show that despite no obvious effects on water nutrients or quality, disturbed and artificial beaches influence the infaunal crustacean biodiversity/community in the classic manner of a disturbance. Furthermore, our results indicate that amphipods may be better indicators of disturbance compared to isopods, as the numbers of isopods were too low to be used in statistically robust analyses. With increasing tourism and corresponding development of artificial beaches in Okinawa Island, it is clear more research needs to be done on this subject.

Human impact on sandy beach vegetation along the southeastern Adriatic coast

AbstractWe compared the zonation of vegetation and connectivity of coastal plant communities between two distinct areas, one in Montenegro and another in Albania, that differ in terms of human impact, mainly through tourism activities. Transect plots were used to gather data about plant cover and communities, their zonation and connectivity. For description of communities multivariate methods were used and for distribution zonation we used gamma connectivity and richness of boundaries. We found that the transects of vegetation zonation from Albania, with better preserved sites, were richer in the number of boundaries, with more varied combinations of boundaries and the pattern of zonation was also more diverse. On the other hand, there were two plant communities found only in Montenegro. The more impacted transects on the disturbed beaches from Montenegro were also more unidirectional from sea to hinterland but with less ideal zonation. Plant communities from Albania were distributed more straightforwardly but contacts between them were in both directions. The less disturbed beach had zonation very similar to potential vegetation, while plant communities of the touristic beach were fragmented or even substituted by replacement communities. Coastal dune systems in Albania are still well preserved, therefore monitoring and protection measures are recommended.

Efectos del disturbio humano sobre la dinámica poblacional de Ocypode quadrata (Decapoda: Ocypodidae) en playas del Caribe mexicano

The ghost crab Ocypode quadrata is a relevant species in the Western Atlantic beaches, and has been proposed as an indicator of human impact in these ecosystems. Eventhough some studies have covered various aspects of its natural history, no evaluations on the effects of human disturbance on its population dynamics have been made. This work compared the abundance, growth, and mortality of O. quadrata in two disturbed beaches (Aventuras and Majahual) and two preserved beaches (Xcacel and Puerto Angel) from the Mexican Caribbean. For this, nine samplings were made on each beach (every two to three months) between March 2013 and November 2014. Crabs were collected manually by three people, during the night first hours and for one hour, and a total area of 9 000 m2 per beach. The crabs were measured, weighed, and separated into three groups: juvenile, male and female; while abundance was estimated by the number of collected crabs, and growth parameters were estimated using length frequencies. A total of 1 047 crabs were sampled in the four beaches; a higher crab abundance was found in the preserved beaches, but significant differences were only found between Puerto Angel and Majahual (Tukey, p<0.05). The adult-juvenile ratio was 1:1 in Xcacel and Aventuras, while in Majahual, more juveniles than adults were collected; and Puerto Angel had more adults than the juveniles. The size structure at Xcacel ranged from 4-32 mm, but in the rest of the beaches the minimum size was 5 mm. The maximum size at Aventuras, Majahual and Puerto Angel were 27 mm, 25 mm and 30 mm, respectively. The modal progression analysis of length’s pooled data, revealed the presence of at least two groups of ages in all beaches. For all beaches, individuals smaller than 10 mm length were collected in almost all sampling months, indicating a continuous recruitment throughout the year. The length-weight relationship of the ghost crab was found isometric in the two preserved beaches, and negative allometric at the two impacted beaches. Crabs from Puerto Angel showed the highest body condition (Tukey, p<0.05). K-values ranged from 0.6-0.97/year and L∞ from 29.0 mm to 33.6 mm with higher values for the two preserved beaches. The highest mortality values were found in Xcacel and Aventuras. In the disturbed beaches, the destruction of the dunes, the mechanical cleaning and the removal of organic matter, seem to be the main causes that lead to a low abundance of crabs, their slower growth and higher mortalities. However, in the best preserved beaches, biological interactions appear to be the most important aspects in regulating the population dynamics of this species. These results supported the information that the ghost crab is a good indicator of human disturbance, and its population changes were clearly measurable and comparable among protected and impacted beaches; these results are also relevant for the management of sandy beaches in the Mexican Caribbean.

DENSITY AND REPRODUCTIVE PATTERN OF Rhinoclavissinensis, Gmelin 1791 (GASTROPODA: CERITHIIDAE) AT THE KRAKAL BEACH, YOGYAKARTA

&lt;p&gt;Krakal Beach Yogyakarta was the most disturbed beach among others in Yogyakarta in term of shells exploitation. Those shells had been traded not only locally at Krakal Beach, but also to Kukup Beach, Baron Beach,Yogyakarta city and for export purpose in the form of raw or handicraft material. Those activities makes the beach condition even much worse. &lt;br /&gt;Some researches were done to reveal whether exploitations were done by tourists (Andiet al. 2005) or local people (Zahidaet al. 2005), and the researched showed that it caused by local people. Further research wanted to elucidate the intensity and volume of harvested shells (Zahida and Sinulingga 2004), and the results showed that more shells were harvested before adults. This was an indication of overharvesting. &lt;br /&gt;Overharvesting or commonly called as overfishing status of the shells exploitation was studied in Krakal Beach, Yogyakarta. King (2003) stated that the exploitation of gastropods for their shells is unquantified, but may account for a much larger live catch weight than does exploitation for food. The aim of this research was to study the density and reproductive pattern of R. sinensis from Krakal Beach, Yogyakarta.&lt;/p&gt;

The ecological effects of beach sand mining in Ghana using ghost crabs (Ocypode species) as biological indicators

Sandy beaches are habitat to many invertebrate biodiversity and threatened vertebrate species. However, extraction of sand is widespread along many developing nations' beaches destroying the ecosystem services the area provides. This study assessed the ecological impacts of beach sand mining on three beaches in the Central Region of Ghana over a four month period, using ghost crabs as a biological indicator. Beaches were categorized as near-pristine, moderately disturbed and highly disturbed. Crab burrows were counted and their diameters measured. Mean burrow density and diameters were significantly higher at the near-pristine site (ANOVA, p < 0.001) compared to the moderately disturbed and highly disturbed beaches, whilst no significant differences occurred between mean burrow densities and diameters at moderately and highly disturbed beaches (ANOVA, p > 0.05). Beach sand mining was found to negatively affect ghost crab populations indicating a critical need for local municipal authorities to identify more sustainable and less damaging sources of sand for the construction industry.

Meiofauna and its sedimentary environment as an integrated indication of anthropogenic disturbance to sandy beach ecosystems

The accuracy and applicability of the Nematode/Copepod index (N/C) in monitoring the effects of environmental disturbances is controversial. In this study, we used an integrated approach that includes both meiofauna and the sedimentary environment to demonstrate a tourism-induced disturbance gradient among sampled beaches. We also analysed the relationships between meiofauna and environmental factors. The results showed that disturbed beaches were characterised by high values of meiofauna abundance, chlorophyll a content, total organic carbon content and N/C but lower levels of dissolved oxygen. The chlorophyll a and dissolved oxygen contents were found to be the most important factors for explaining the disturbance gradient amongst the beaches. The N/C index had a positive relationship with chlorophyll a and a negative relationship with dissolved oxygen. There was no significant relationship between N/C index and total organic carbon content.

Rapid Assessment of Anthropogenic Impacts of Exposed Sandy Beaches in Ghana using Ghost Crabs (&lt;i&gt;Ocypode&lt;/i&gt; Spp.) as Ecological Indicators

We applied a rapid assessment methodology to estimate the degree of human impact of exposed sandy beaches in Ghana using ghost crabs as ecological indicators. The use of size ranges of ghost crab burrows and their population density as ecological indicators to assess extent of anthropogenic impacts on beaches was explored in this study. For each site, three transects were laid perpendicular to the shoreline over a 100 meter distance at 50 m intervals, i.e., at reference points 0, 50 and 100 meter points. Sampling locations were randomly selected along the three transects using a 1 m x 1 m quadrat. Measurements were done twice weekly for a period of four weeks. The results showed that even though the moderately disturbed beach had higher burrow density than the disturbed beach on the average, the difference is not statistically significant (T-test; p > 0.01). However, mean burrow diameter at the moderately disturbed site was statistically found to be significantly larger than for the disturbed site (T-test; p < 0.01). We conclude that burrow sizes is a good estimator for verification of human impacts of exposed sandy beaches. It confirms that burrow density even though an important factor, may not necessarily be a significant estimator of the impacts of human activity on beaches. On this basis, it appears that the estimations of the diameter of burrows of crabs of the Ocypode genera provides a rapid tool for impact verification of sandy beaches and for use in environmental quality monitoring of beach programs in coastal areas.

Recovery of sandy beach and maritime forest vegetation on Phuket Island (Thailand) after the major Indian Ocean tsunami of 2004

AbstractQuestion: How rapidly has the sandy beach and maritime forest vegetation on Phuket recovered and regenerated after the impact of the major Indian Ocean tsunami of 2004? What are the characteristics of sandy beach species for regenerating their populations and the invasion patterns of originally non‐sandy beach species or other newcomers after the tsunami?Location: Phuket Island, southern Thailand.Methods: Species composition of beaches was studied on the same research plots 6 months before and 9 months after the tsunami. The changes in individual species cover before and after the tsunami were determined by χ2 tests. Change in community composition was analysed by detrended correspondence analysis. The relationship between species and environmental factors was analysed by canonical correspondence analysis.Results: The sites disturbed by the tsunami were often invaded by annuals, especially grasses and asteraceous plants, rather than by perennials. In contrast, species with clonal growth by stolons decreased significantly. Factors determining the species habitat differences were soil hardness (penetration resistance of sandy soil), per cent silt content, soil water content and beach management. Habitat differences among originally non‐sandy beach herbaceous species that expanded their population or moved to the coast after the disaster were defined by sand accretion or erosion caused by the tsunami. Many sandy beach herbaceous communities changed into Dactyloctenium aegyptium communities because of the tsunami were originally constituted by non‐sandy beach D. aegyptium with Cenchrus echinatus. Although the forest floors of most maritime forests were invaded by originally non‐sandy beach Tridax procumbens, Eleusine indica or D. aegyptium because of the tsunami, this did not result in a change in the vegetation unit, because species' loss was restricted to the understorey. In time, these forests will recover their previous community composition.Conclusions: Our results suggest that originally non‐sandy beach native species invaded the disturbed beaches rapidly after the tsunami but their habitats differ. Sites where sand accumulated on a beach because of the tsunami were invaded by D. aegyptium and E. indica, whereas soil erosion permitted invasion by Digitania adscendens. Tridax procumbens establishes rapidly on wet sites with hard soil, high per cent silt content and low beach management pressure. Sandy beach species with subterranean long rhizomes are strongly tolerant of such disasters. We concluded that the species composition of the beaches disturbed by a temporary large disaster is determined by dormancy and growth forms, with radicoid form being influential.

Tourism impairs tiger beetle (Cicindeldae) populations – a case studyin a Mediterranean beach habitat

Adult activity and larval development of Lophyridia concolor (Dejean) was examined in three sections of a marine beach: (1) an undisturbed section; (2) a section occasionally used by tourists; and (3) a heavily disturbed beach section. Although the activity of adult tiger beetles was similar at all three sites in spring, it diverged during the tourist season. The adults reached a high activity with two maxima on the natural beach, but it was 40% lower in the occasionally used section. The adult activity decreased abruptly without visible maxima in the tourist area. Larval activities showed similar trends. First and second instar larvae were practically absent from the heavily disturbed section. The reduced tiger beetle activity was most likely caused by disturbance and modification of habitat by the tourists. Mechanisms of this impairment are discussed. The results might be of importance for several beach inhabiting invertebrates in the Mediterranean area. Persistently high levels of tourist traffic on beaches might lead to local extirpation, as the decline of Lophyridia a. aphrodisia (Baudi), another Turkish tiger beetle species, shows.

Biologia e anatomia funcional de Donax gemmula Morrison (Bivalvia, Donacidae) do litoral de São Paulo, Brasil

Donax gemmula Morrison, 1971 ocorre em praias arenosas da costa sudeste-sul do Brasil até o Uruguai. Espécimes foram coletados na Praia de Barequeçaba, São Sebastião, Estado de São Paulo, Brasil. O comportamento do animal foi registrado "in situ" e em aquários e a morfologia funcional a partir de espécimes dissecados sob estereomicroscópio; detalhes da anatomia foram obtidos a partir de cortes histológicos. A concha pequena, lisa, subglobosa, e o pé grande, muscular, provido de um par de músculos elevadores bem desenvolvidos, permitem escavação rápida, vital em praias sujeitas à intensa ação de ondas onde a espécie vive. Aparato bissal vestigial ocorre desde a fase juvenil à adulta e este donacídeo de vida livre, infaunal, não migra acompanhando o ritmo das marés. As margens do manto possuem prega mediana duplicada; além de tentáculos captados, as pregas medianas possuem tentáculos sensoriais filiformes, longos, estes últimos restritos à região posterior do animal. A espécie tem hábito alimentar suspensívoro seletivo, o qual é revelado pela presença de ctenídios grandes, completos e homorhábdicos, palpos labiais pequenos e muito seletivos, intestino curto, fracamente sinuoso, separado do saco do estilete cristalino, e tentáculos ramificados formando um crivo em torno da abertura inalante.

Photoautotrophs and the microaggregation of sand in a freshwater beach-dune complex: Implications for sediment transport by wind

A temporal investigation of sediments in a freshwater beach-dune complex on the northeastern shore of Lake Ontario shows that photoautotrophic microorganisms are important in particle aggregation and therefore, surface stabilization against wind erosion. The percentage of wind stable aggregates > 0.84 nun dia is greatest in panne areas, showing substantial increases in early spring. Considerable diversity of photoautotrophs is found in these moist, low lying areas with cyanobacteria, chlorophytes and diatoms present in an active state. Virtually no aggregation is observed in sediments from either the dune ridges or portions of the beach surface which are raked on a daily basis to remove detritus. These disturbed beach surfaces are mobilized by strong autumn winds. Although chlorophytes and cyanobacteria were cultured in the dune sediments, low chlorophyll a concentrations suggest that these microorganisms were not actively growing. In comparison, aggregation is evident in natural, undisturbed beach sediments, especially in midsummer. This increase is positively correlated with chlorophyll a concentration and number of genera. An exponential relationship is observed between chlorophyll a concentration and the percentage of aggregates (> 0.84 mm) in panne and natural beach samples. These aggregates contribute to the stability of these areas to wind transport.