Mollusk Composition Research Articles

Peculiarities of the Species Composition, Abundance and Biotope Distribution of Mollusks Fam. Sphaeriidae in Rivers with a Many Lakes in the Catchment Area (by the Example of Water Courses of the Onega Lake Basin)

Using the example of the rivers of the Onega Lake basin, the species composition of mollusks of the Sphaeriidae family, their abundance, biomass, and contribution to benthic communities in rivers with many lakes in the catchment areas were analyzed. Patterns of spatial distribution of species across biotopes and gradients of environmental variables were traced. 26 species of mollusks of this family were identified, among them European-Siberian species predominate. Most of the species of mollusks of the family Sphaeriidae found by us have wide ecological ranges and are found in water bodies of various types. It was found that the contribution of Sphaeriidae to the species richness and functioning of aquatic communities in rivers in the conditions of branched lake-river systems (Lake Onega basin) exceeds the values usual for rivers with a small number of lakes in the catchment area. Using the ANOSIM and PERMANOVA methods, it was proved that the species composition of rocky rapids and riffles, sandy rifts and soft bottom soils is different. Using the IndVal test, seven species were shown to have a statistically significant association with one of these biotopes, and four of them, with rocky bottoms of river rapids and riffles. Using the NMDS method, it was shown that the greatest changes in the species composition of representatives of Sphaeriidae are observed when environmental conditions change from small streams with slow current and brown water to large rivers with fast current and clear water.

Changes in Composition of Mollusks within Corallina officinalis Turfs in South Istria, Adriatic Sea, as a Response to Anthropogenic Impact

A very common intertidal alga, Corallina officinalis, serves as a refuge for numerous invertebrates within its settlements. The composition and structure of invertebrates may differ in relation to different natural or human-induced stress, and this study examined the effects of anthropogenic impact on the abundance and diversity of mollusks residing within C. officinalis settlements. Sampling was conducted during two seasons (Season 1 = algae’s maximum vegetation growth and Season 2 = algae’s minimum vegetation growth). Gastropods and bivalves made up 50% of all invertebrates identified, with a total of 47 species of gastropods, 25 species of bivalves, and one polyplacophoran species recorded. Considering the overall count of individuals, 4562 gastropods, 21,738 bivalves, and 260 polyplacophorans were collected from all available Corallina samples. The results indicated that locations under human impact showed a reduced number of the most abundant gastropod and bivalve species and a reduced average number of individuals.

Ultradian rhythms in shell composition of photosymbiotic and non-photosymbiotic mollusks

Abstract. The chemical composition of mollusk shells is a useful tool in (paleo)climatology since it captures inter- and intra-annual variability in environmental conditions. Trace element and stable isotope analysis with improved sampling resolution now allows in situ determination of the composition of mollusk shell volumes precipitated at daily to sub-daily time intervals. Here, we discuss hourly resolved Mg / Ca, Mn / Ca, Sr / Ca, and Ba / Ca profiles measured by laser ablation inductively coupled plasma – mass spectrometry (ICP-MS) through shells of the photosymbiotic giant clams (Tridacna maxima, T. squamosa, and T. squamosina) and the non-photosymbiotic scallop Pecten maximus. Precise sclerochronological age models and spectral analysis allowed us to extract daily and tidal rhythms in the trace element composition of these shells. We find weak but statistically significant expressions of these periods and conclude that this cyclicity explains less than 10 % of the sub-annual variance in trace element profiles. Tidal and diurnal rhythms explain variability of, at most, 0.2 mmol mol−1 (∼ 10 % of mean value) in Mg / Ca and Sr / Ca, while ultradian Mn / Ca and Ba / Ca cyclicity has a median amplitude of less than 2 µmol mol−1 mol mol−1 (∼ 40 % and 80 % of the mean of Mn / Ca and Ba / Ca, respectively). Daily periodicity in Sr / Ca and Ba / Ca is stronger in Tridacna than in Pecten, with Pecten showing stronger tidal periodicity. One T. squamosa specimen which grew under a sunshade exhibits among the strongest diurnal cyclicity. Daily cycles in the trace element composition of giant clams are therefore unlikely to be driven by variations in direct insolation but rather reflect an inherent biological rhythmic process affecting element incorporation. Finally, the large amount of short-term trace element variability unexplained by tidal and daily rhythms highlights the dominance of aperiodic processes in mollusk physiology and/or environmental conditions over shell composition at the sub-daily scale. Future studies should aim to investigate whether this remaining variability in shell chemistry reliably records weather patterns or circulation changes in the animals' environment.

Species Composition and Ecology of Mollusks of the Unionidae and Corbiculidae Families of the Zaamin Water Storage

The material was collected in the waters of the Zaamin water storage in the summer, autumn and spring seasons of 2018-2023. Collected 67 samples, 244 specimens of mollusks. The determination was carried out according to generally accepted methods. The species composition of mollusks and their ecological state were studied. It was revealed that Euglesa (Euglesa) turkestanica, Euglesa (Pseudeupera) turanica and Odhneripisidium (Kuiperipisidium) sogdianumare common in the waters of the upper part. Corbicula fluminalis, C. (Corbicula) tibetensis, and C. (Corbicula) ferghanensis inhabit the deep-water biotopes of the southern coast of the water storage. A total of 8 species and 1 subspecies of bivalves have been identified.

Komposisi dan Kelimpahan Moluska (Gastropoda dan Bivalvia)

This study aims to determine the composition and abundance of mollusks (Gastropods and Bivalves) in the Aek Pala River, Labuhanbatu Regency. The method used is purposive random sampling. Sampling was carried out using a net source. The results showed that the Gastropod groups found were Pachychilidae, Ampullaridae, Littorinidae, Nassaridae, Thiaridae, Hydrobiidae, Tateidae, Spiraxidae, Vivipararidae and Batillariidae, while the Bivalvia groups were Corbiculidae and Curbulidae. In conclusion, the composition of mollusks found were 10 families of Gastropods and 2 families of Bivalves.
 Keywords: Bivalves, Gastropods, Abundance, Composition, Molluscs

Functional variations of mollusks along an environmental gradient in a coastal lagoon of the Southern Gulf of Mexico

Despite mollusk species play important ecological functions in estuaries, most studies of their assemblage’s variations are based on traditional taxonomical approaches. Biological trait analysis is used in the present work to explore the relationships of the functional composition of mollusks with the environmental gradient along a coastal lagoon of the Southern Gulf of Mexico. Sampling was conducted monthly during a year in soft bottoms and subtidal stilt roots of red mangrove at six sampling sites along the lagoon. In total 24 mollusc species were collected and fitted to a particular category of three biological traits. Spatio-temporal variability of the functional composition of molluscs and their relationships with environmental variables were assessed using three approaches. Functional variations of the molluscan assemblages were detected along the lagoon using the three approaches, showing significant correlations to salinity. Nonetheless, the functional groups (FG) and the community weighed (CWM) mean traits approaches showed a clearer spatial pattern of the functional composition than the functional diversity (FD) approach The FG and the CWM approaches used in the present study could help to broadening the ecological studies of the estuarine systems of the Gulf of Mexico, particularly those aimed to assess the relations between the biological components and environmental variables in order to assess functioning of these ecosystems.

Non-destructive raman spectroscopic determination of freshwater mollusk composition, growth, and damage repair.

Increased acidification of aquatic habitats due to climate change is damaging mollusks. Non-destructive methods for analysis are necessary to study these endangered species. We analyzed five Unionidae gastropods using Raman spectroscopy. Shells were primarily composed of aragonite, a polymorph of calcium carbonate found in shell microstructure. Lattice mode Raman peaks from vaterite, a thought to be rare polymorph of calcium carbonate, were identified in each mollusk. Vaterite is present in mollusks at instances of shell damage and subsequent repair. We demonstrate that Raman spectroscopy is sensitive to vaterite, and it may not be as rare as previously thought. We also collected Raman spectra across the interior of Lampsillis fasciola. This data was analyzed through multivariate analysis, combining Principal Component Analysis with Linear Discriminant Analysis (PCA-LDA). Results of PCA-LDA correlate with growth of the mollusks, demonstrating that Raman spectroscopy combined with multivariate analysis could be used to monitor shell growth.

Taxonomy, palaeoecology and stratigraphy of the middle Miocene mollusk fauna from the Gračanica coal pit near Bugojno in Bosnia and Herzegovina

During the early and middle Miocene, the Dinarides Lake System (DLS) was a major hotspot of freshwater mollusk diversity in southeastern Europe. The numerous intramontane lake basins, originating by combined effects of tectonic subsidence and humid climate, accumulated thick lacustrine successions. Diagenetic overprint and leaching of these carbonate-rich deposits have facilitated insights to faunal contents for only a few basins up to the present. We contribute to filling this gap by documenting for the first time a mollusk fauna from the Bugojno Basin in Bosnia and Herzegovina. The fauna originates from a coal-bearing succession representing a gradual flooding of the coastal wetlands followed upwards by the establishment of perennial lacustrine settings in the basin. Our taxonomic analyses documents 17 gastropod and two bivalve species. New to science are IIllyricocongeria forcakovici nov. sp., Prososthenia krijgsmani nov. sp. and Bania goehlichae nov. sp. The palaeoecological analysis based on quantified samples shows distinct shifts in mollusk composition and abundance. The terrestrial taxa are restricted to the coal-bearing interval of the section; melanopsids, neritids and hydrobiids are abundant in deltaic and littoral settings, whereas bivalves are frequent in littoral and sublittoral environments. In line with previous results, which have evidenced a high degree of intralacustrine radiation in the DLS, the Lake Bugojno fauna shows a low to moderate level of similarity to other DLS faunas. The dissimilarity may partly also result from its younger age as suggested by the presence or absence of regional biostratigraphic marker species.

The composition of mollusks in mangrove ecosystem conservation area Bagek Kembar, West Lombok

Mangrove association mollusks was one of the indicator to describe the status of mangrove ecosystem’s health. This research aimed to analyze the condition of mangrove rehabilitation based on the composition of association mollusks compared with non-rehabilitation area which resulted from a natural succession. It held on July 2019 at mangrove conservation area Bagek Kembar, West Lombok. Data collection method used stratified random sampling by placed some plots sized 1x1 m randomly in a larger plot (10x10 m) which have been determine randomly before. The result showed that there are 24 species of association mollusks which belong to 11 families found in these area. The abundance of mollusks in natural and rehabilitation mangrove was different which is in a row 50.2647 ind/m 2 and 88.4 ind/m 2. Cerithidea cingulata has the highest abundance among the other species with the number of abundance 48.8 ind/m2 in non-rehabilitation ecosystem and reach 29.17 ind/m 2 in rehabilitation area. Based on this research, the condition of mangrove conservation Bagek Kembar still categorized as non-stable condition for supporting the survival of mangroves associated mollusks.

Palaeoenvironments of the Manych Valley at the End of Late Pleistocene Based on Rodent and Mollusk Data from Sanmanych (Rostov District, Russia)

A thorough consideration is given to the geological, palaeotheriological and malacological materials obtained from the Pleistocene Sanmanych locality, which is the only locality with mammal fauna in the Manych depression (46°24′53″ N, 42°36′25″ E). The brackish-water mollusk composition indicated that the bone-bearing series should be correlated to the Early Khvalynian transgression. The fossil record gives an insight into the palaeoenvironment at the time that the Caspian Sea water broke through the Manych depression into the Black Sea basin. The faunal evidence points to arid conditions and a cool climate. The rodent species composition is rather poor; it exclusively includes species indicative for an open environment, which suggests a wide spread occurrence of steppe and semi-deserts in the Manych valley during the Late Glacial (~16–12 ka BP).

ЭВОЛЮЦИЯ ПРИРОДНОЙ СРЕДЫ КАСПИЯ В УСЛОВИЯХ ГЛОБАЛЬНЫХ ИЗМЕНЕНИЙ КЛИМАТА

Evolution of environment of the Caspian Sea in the conditions of global climate changes is considered for two multi-scale temporary periods: the last climatic macrocycle (marine isotope stages, MIS, 5-2) and the Holocene (MIS 1). Both of them are characterized by considerable climatic changes. The Caspian Sea reacted to climatic events of MIS 5 epoch by the development of two transgressive basins - the warm-water Late Khazarian and moderately warm-water Hyrcanian basins. The Atelian regression was answered to the MIS 4 glacial stage and initial phases of interstadial warming MIS 3. The climatic conditions of the second half of interstadial warming were reflected by development of the first stage of the Khvalynian transgression. The transgressive trend of level was interrupted during an epoch of the maximum cold and dryness of MIS 2 stage. During an epoch of glacial degradation the development of Khvalynian transgression was resumed. Climatic events of late glacial epoch, the warming phases Bolling and Allered, got a response in development of the transgressive stage of the Khvalynian basin. Phases of a considerable cold snap (Oldest, Older and Yanger Dryas) were reflected by regressive stages in the history of the Khvalynian basin. The most considerable of them answered to the Yanger Dryas. Development of the Mangyshlakian regression is a response of the Caspian Sea to the continentalization of climate of the Boreal period of the Holocene. In development of the New Caspian transgression, the three transgressive stages are established. They are closely connected with regional climate changes. The composition of mollusks of the Caspian Sea represents the result of evolutionary processes in the Pleistocene faunae occurring in the conditions of climatic changes and transgressive and regressive rhythmics of the basin. The New Caspian (Holocene) complexes reflect the change of biotic conditions of the basin - the invasion of the Black Sea species. The invasiv species and acclimatizin species made much more essential changes to structure of the biodiversity, than it is caused by natural factors. The natural ecosystems underwent the anthropogenous transformation, turning the unique ecosystems of the Caspian Sea created for its Pleistocene history into similarity of the Azov-Black Sea ecosystems.

Mollusk communities differ between microenvironments within a shallow lake in the Pampean Region, Argentina

El objetivo de este trabajo es comparar la distribucion de los ensambles de moluscos en diferentes sitios dentro de un lago somero pampeano y evaluar la relacion que existe entre la abundancia y la riqueza de moluscos y las variables ambientales. Los moluscos mostraron una distribucion en parches, pero no azarosa. Tres de los sitios que eran mas profundos y que estaban dominados por macrofitas emergentes estuvieron caracterizados por mayores abundancias de los gasteropodos Heleobia parchappii, Physa acuta y Uncancylus concentricus. En contraste, los otros dos sitios que estuvieron caracterizados por menores profundidades, menores pH, mayor diversidad de vegetacion y temperaturas del agua mas altas estuvieron dominados por Biomphalaria peregrina y por el bivalvo Musculium argentinum. Este estudio evidencia la distribucion en parches de moluscos dulceacuicolas en lagos someros de la ecorregion pampeana donde las variables ambientales explican de forma parcial la distribucion local dentro del lago.

On the Taxonomic Composition of Mollusks from the Tavda Formation of Western Siberia

The taxonomic composition of bivalves and gastropods from the clays of the Tavda Formation was studied from the Kyshtyrla Quarry, 23 km south of the city of Tyumen and from the drill core of Boreholes 8 and 11 south of the city of Omsk. The Kyshtyrla malacofauna is represented by siderite molds and imprints, rarely entire shells, sometimes bivalved specimens, among which 19 taxa were identified. The borehole material contained eight species of eight genera. These assemblages show striking resemblance to the Chegan Fauna of North Ustyurt, Aral and Turgay, suggesting their similar age and direct paleogeographic connections between these basins. Both assemblages indicate marine, probably slightly brackish-water environments and relatively shallow-water deposition below the surf zone in conditions varying from normal aeration (favorable for benthic organisms) to dysoxic.

Riqueza y distribución vertical de los moluscos del litoral rocoso de la provincia de Islay, Arequipa, al sur del Perú

El litoral rocoso es un ecosistema heterogéneo en el que se distinguen una franja supralitoral, una zona mediolitoral y una franja infralitoral, al reconocer a las especies de moluscos como indicadoras de una zonación vertical. Este trabajo contribuye al conocimiento de la riqueza y la distribución vertical de los moluscos intermareales para la provincia de Islay, Arequipa, Perú. Se realizó una búsqueda intensiva en los meses de noviembre y diciembre del año 2013, para poder determinar la riqueza y se establecieron tres cuadrantes de 25 x 25 cm de lado distribuidos perpendicularmente a la línea costera con 14 repeticiones en los 7 sitios de estudio, para establecer su distribución vertical. Se utilizó un análisis de componentes principales (ACP), un escalamiento multidimensional no métrico (nMDS) y curvas de rango-abundancia para la determinación de la distribución vertical, y un análisis de similaridades (ANOSIM) para determinar diferencias entre la composición de moluscos entre los sitios de estudios y las subzonas del litoral. Se encontraron un total de 57 taxones, donde Echinolittorina peruviana fue la especie más representativa en la franja supralitoral, Perumytilus purpuratus para la zona mediolitoral y Tegula atra para la franja infralitoral. No se presentaron diferencias significativas en la composición de moluscos entre los sitios de estudio, pero sí entre las subzonas, al ser la zona mediolitoral la que presentó mayor riqueza y abundancia de organismos. La similitud fue mayor entre las subzonas medio e infra- con respecto a la supralitoral.

Mollusk Response to Anthropogenic Impacts: An Example from Cross River Estuary, South Eastern Nigeria

The Mollusks of the Cross-River Estuary were sampled monthly between June and August during the rainy season using the direct search and litter-sieving methods. The results show that the extent of alteration of the natural ecosystem from anthropogenic activities could be deduced using the variations in numerical abundance and composition of mollusks in the environment. The most dominant mollusk communities in this study are represented by Neritina glabrata (30.29% during the first sampling and 49.08% during second sampling), Pachymeninx aurita (30.28% during the first sampling and 24.15% at second sampling), Tympanotonus Fuscatus (24.90% and 24.87% during the first and second sampling respectively) and Mactra glabrata (7.00% and 2.00% during the first and second sampling respectively). Low numerical abundance was recorded during the first sampling (241 individuals) as compared to the second sampling (381 individuals) which was attributed to the impacts of silt sedimentation caused by the dredging activities on the estuary in the first month of sampling. The general low diversity of mollusks assemblages recorded in this study reflects the strong impacts of anthropogenic activities. This study has demonstrated the fact that mollusk communities can be utilized as important marker for monitoring anthropogenic impacts and the state of health of the aquatic environment. The study however records various sampling variables due to the nature of the sampling methods. In order to obtain more precise data for a reliable assessment of anthropogenic impacts on the Cross-River Estuary, detailed study of the mollusks communities considering variables such as weather, season and salinity is therefore recommended.

Investigating the last glacial Gravettian site ‘Ságvár Lyukas Hill’ (Hungary) and its paleoenvironmental and geochronological context using a multi-proxy approach

Gravettian population during the last glacial maximum (LGM) was sparse in Europe; this is generally related to harsh environmental conditions. Here we report of geoarcheological investigations (physical, chemical and biological data) of the Ságvár site in the Hungarian part of the Carpathian Basin in southeastern Europe. Geochronological control is given by luminescence dating, which places loess accumulation between 20.6±1.4ka and 17.7±1.2ka. This study demonstrates that human occupation at Ságvár did not occur during a rather mild climatic phase, but during a ‘typical’ cold LGM climate. Of the two cultural layers discussed at the section, the upper one can be clearly distinguished in the section by the physical proxy data, while the lower one is observed only in some proxies. Similarly, previous archeological investigations describe a higher tool density in the upper layer. The mollusk composition indicates dry climate for both occupation phases, but the paleoecology of the lower occupation phase suggests also the presence of mosaic spots of wet tundra, which allowed for increased weathering processes in the sediment. These are preserved as indications for weak pedogenesis in the physical and chemical proxy data, although a disturbance of human occupation in the signal cannot be excluded. This study demonstrates the advantages of integrating proxy data of different disciplines.

A critical examination of the possible application of zinc stable isotope ratios in bivalve mollusks and suspended particulate matter to trace zinc pollution in a tropical estuary

The application of zinc (Zn) isotopes in bivalve tissues to identify zinc sources in estuaries was critically assessed. We determined the zinc isotope composition of mollusks (Crassostrea brasiliana and Perna perna) and suspended particulate matter (SPM) in a tropical estuary (Sepetiba Bay, Brazil) historically impacted by metallurgical activities. The zinc isotope systematics of the SPM was in line with mixing of zinc derived from fluvial material and from metallurgical activities. In contrast, source mixing alone cannot account for the isotope ratios observed in the bivalves, which are significantly lighter in the contaminated metallurgical zone (δ66ZnJMC = +0.49 ± 0.06‰, 2σ, n = 3) compared to sampling locations outside (δ66ZnJMC = +0.83 ± 0.10‰, 2σ, n = 22). This observation suggests that additional factors such as speciation, bioavailability and bioaccumulation pathways (via solution or particulate matter) influence the zinc isotope composition of bivalves.

Fish-otoliths from the marine-brackish water transition from the Middle Miocene of the Belgrade area, Serbia.

We describe here the first fossil otoliths from the Middle Miocene (Badenian and Sarmatian) of Belgrade, Serbia. They were obtained from Lower Badenian outcrops at Slanci and from upper Badenian and Sarmatian sediments recovered from four shallow wells near the village of Barajevo. The otoliths from the Lower Badenian of Slanci represent fishes typical for an open marine environment, characterized primarily by the mesopelagic families Myctophidae and Bregmacerotidae, a faunal composition that is also well known from other time equivalent locations in the Central Paratethys. The upper Badenian and Sarmatian composition of the fish fauna, in contrast, is dominated by otoliths of the family Gobiidae, indicating a sharp environmental shift from open marine to shallow water, probably slightly brackish environments, which is also confirmed by the faunal composition of mollusks, foraminifera, and ostracods. Most of the gobiid genera identified in the samples from Barajevo represent small fishes of the so-called sand gobies with Ponto-Caspian affinities, such as Economidichthys, Knipowitschia, or Pomatoschistus, or are entirely endemic to the Ponto-Caspian Basin, such as Hyrcanogobius. Another group of endemic Ponto-Caspian gobies is the first fossil record interpreted to represent the genus Proterorhinus. These and other finds currently being investigated indicate that the origin of the extant, rich, endemic gobiid fauna of the Ponto-Caspian Basin dates back to a crucial time in the development of Paratethys during the Middle Miocene when it segregated from the Mediterranean with the onset of phases of low salinity in the basin. In addition, we briefly discuss the distribution of certain gobiid species during Late Badenian and Sarmatian as it begins to emerge. The following new taxa are described based on fossil otoliths: Hyrcanogobius hesperis n.sp. and Proterorhinus vasilievae n.sp.

Testing the efficacy and reliability of common zooarchaeological sampling strategies: a case study from the Caribbean

Zooarchaeological analysis typically involves implementing a suitable sampling strategy that provides meaningful information representative of a site under investigation. To test the efficacy of how various sampling procedures can influence interpretation of a faunal assemblage, we analyzed in full, a large assemblage of mollusks (minimum number of individuals [MNI] = 58,000+) from the late Ceramic Age (ca. AD 850–1440) site of Coconut Walk on the island of Nevis (northern Lesser Antilles, Caribbean). These remains were recovered from 25 discrete 1 × 1 m units within a larger 5 × 5 m trench that overlaid a dense midden deposit. Using statistical procedures, we compared the results of the number of identified specimens (NISP), MNI, and weight (g) of each mollusk taxon between both units and plana to determine how different sampling strategies would have affected the interpretation of mollusk composition across space and time had different sampling procedures been used. The results reveal that sampling less than 16% (4 out of 25 squares for this study) of a midden is likely to produce results outside of a 95% confidence interval for the population composition, with samples of connected squares having a higher likelihood to lie outside the interval. Discerning change between plana (or layers) may require a larger sample (i.e., 16%+). In addition, samples selected randomly or judgmentally will produce similar results, provided that proper spacing is given between units. The data in this case suggest that the midden was efficiently sampled for midden composition and key species at a rate of 16% of the surface area.

Multi-proxy evidence of Late Quaternary environmental changes in the coastal area of Puerto Lobos (northern Patagonia, Argentina)

A multidisciplinary approach involving geomorphology, taxa composition of mollusks and taphonomy performed on bivalve shells, linked to mineralogical and microstructural analyses, provide evidence of Late Quaternary environmental changes in the coastal area of Puerto Lobos, in northern Patagonia. Digital elevation models (DEMs) showed a beach ridge system developed parallel to the coast, indicating sea level variations during MIS1, MIS5e, and earlier in the Pleistocene. These ridges can be correlated with other marine ridges along the Patagonian coast, showing a similar geomorphological pattern and similar temporal evolution. In relation to faunal composition, when comparing the Pleistocene with the Holocene, the most relevant differences are the presence of Tegula atra and Mactra patagonica in the Pleistocene sediments and a diversification of taxa in the Holocene. During the late Holocene, the coastal area of Puerto Lobos also recorded a faunal shift in which species belonging to the Magellan Province displaced the fauna of the Argentinean Province to the north, probably in coincidence with the Little Ice Age (LIA). Taphonomic analysis on Glycymeris longior and Venus antiqua shells, two common taxa in these beach ridges, indicate greater energy in the depositional environment correlated with the youngest Holocene beach ridge. These shells exhibited taphonomic differences between them in relation to fracturing, explained on the basis of higher elasticity in the G. longior shell than in V. antiqua shell, because of its crossed lamellar microstructure.