Molluscan Assemblages Research Articles

The use of malacological analysis in studies on anthropogenic transformations in microhabitats: an example from the Cracow region, southern Poland

The presented study is dedicated to the assessment of the scope and degree of anthropopressure, and the dependence of its intensity on the characteristics and nature of micro-environments. The research was based on the subfossil remains of molluscs. Eleven profiles of Late Holocene sediments in the Dulówka valley near Cracow were subjected to malacological analysis. In the upper part of the valley, there are calcareous tufas containing rich molluscan assemblages with a large share of shade-loving species. In the lower part, malacofauna dominated by open-country snails occurs in fluvial sediments. Radiocarbon dating has shown that mollusc-bearing deposits represent the last 2,000 years. The diversity of ecological features of molluscan assemblages in different parts of the valley depends on the intensity of anthropopressure. In the upper part, natural forest communities have survived to the present day, and anthropopressure has only been marked to a limited extent. The lower section has undergone a major transformation, mainly due to deforestation and the development of agricultural areas. Unfavorable terrain conditions for the human economy should be considered the major cause of the low anthropopressure intensity in the upper part of the valley. The malacological analysis used in the study allowed showing a significant diversity of microhabitats within the valley and its uneven susceptibility to human interference in natural processes.

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.

MOLLUSCAN LIVE-DEAD FIDELITY OF A STORM-DOMINATED SHALLOW-MARINE SETTING AND ITS IMPLICATIONS

ABSTRACT Actualistic studies are important for evaluating the fidelity of fossil assemblages in representing the living community. Poor live-dead (LD) fidelity in molluscan assemblages may result from transport-induced mixing. Large-scale mixing is more common in siliciclastic settings with a narrow shelf, high sedimentation rate, and those that are frequented by episodically high-energy events. Chandipur-on-sea, on the east coast of India has an optimal setting to promote such conditions. By studying the LD fidelity and modeling size-frequency distribution (SFD) of the fauna, we attempted to evaluate the contribution of “out-of-habitat” versus “within-habitat” mixing in developing the molluscan death assemblage. The correlation between the composition of live (LA) and death assemblages (DA) was insufficient; unlike LAs, the DAs do not show environmental partitioning in ordination space. A numerical simulation of the shell size frequency distribution (SFD) for DAs from LAs was compared with the observed SFD of the DAs. The results of this simulation indicate that DAs are not likely to be a product of within-habitat mixing. DAs probably received considerable input via regional transport, facilitated by frequent tropical cyclones affecting the coast of Odisha. Chandipur receives a large proportion of cyclones originating above 15°N, which causes a high degree of lateral transport and shell mixing between 15° to 21°N, explained by the high compositional similarity of species within this latitudinal extent. Our study highlights the significance of out-of-habitat transport in shaping the regional distribution of marine fossil assemblages, especially in storm dominated siliciclastic shallow-marine settings.

Thanatocoenoses of mollusc shells in the north-western part of the Black Sea

Following death, mollusc shells become elements of thanatocoenoses of bottom and coastal deposits. At the early stages of succession of storm strands, the conservation of mollusc shells in the coastal deposits is high, which allows to obtain a larger number of shells to determine their traits. The probability of finding shells of rare mollusc species in the coastal strands is significantly higher than in bottom grab samples. Therefore, the taxonomic composition of the thanatocoenoses may correspond to the actual composition of mollusc assemblage in the adjacent coastal waters. Determination of the maximum age of molluscs from coastal emissions by sclerochronological methods can be more accurate characteristics of the lifespan of the considered mollusc species. Wind waves are one of the hydrodynamic processes influencing the formation of coastal emissions. The maximum wave activity in the coastal zone of the sea contributes to an increase in the deposition of storm emissions in the coastal zone. Studies of thanatocoenoses of marine molluscs in storm emissions in the north-western part of the Black Sea were carried out at three test sites, differing in the degree of wave load on the coastal zone. Analysis of coastal emissions in different parts of the coastal zone — various distance from the water's edge—allows us to determine the frequency and power of wave activity, as well as to identify the dominant species of macrozoobenthos in each area. The composition and quantitative characteristics of storm emissions created by wave activity of various intensities demonstrates the relationship between benthic biocoenoses of molluscs and thanatocoenoses of the coastal zone. The dominance of bivalve mollusc shells in emissions corresponds to the ruling species of molluscs in benthic biocoenoses. Shells of molluscs of the family Mytilidae were dominant in coastal emissions of the analysed areas. The maximum concentration of aquatic organisms is presented in emissions located near the edge of seawater. A dependence between the total mass of biogenic components in coastal sediments and different distances from the water edge has been revealed for the north-western part of the Black Sea.

Paleoclimate and changing composition of the Paleogene-Neogene shallow Molluscan Assemblages of Patagonia

A detailed compilation and updated taxonomy of the shallow molluscan assemblages of the Paleogene-Neogene of Patagonia was performed. Together with the Sr-chronostratigraphic framework developed during the last decade, five assemblages of Danian, late middle Eocene, latest Oligocene-early Miocene, middle Miocene and late Miocene ages were recognized. Temporal variation in the composition of these assemblages reflects the successive transient hyperthermal events superimposed to the global cooling trend in the sea surface temperatures during Cenozoic times. Tropical or warmest subtropical temperatures in the region during the Danian and late middle Eocene times coincide respectively with the Dan-C2 and the Latest Danian Event, and the Middle Eocene Climatic Optimum events. Tropical taxa, represented by Tethyan and warm-Cosmopolitan genera constitute 27.6% and 31.3% of the fauna respectively. The declining participation of Paleogene warm-genera, comprising just 15.3% of the fauna, coupled with the massive appearance of the subtropical Neogene Southern elements, reveals a decrease in sea surface temperatures during the latest Oligocene-early Miocene interval until the establishment of warm-temperate conditions in the area. Although lower than during the Paleogene, temperatures should have been higher than today, in coincidence with the late Oligocene warming and the multiple warming events in the early Miocene. The middle Miocene records the first large occurrence of Caribbean taxa that will be continue being important components of the fauna during the late Miocene. The contribution of warm-taxa to the faunas rose from 15.3% in the early Miocene to 23% and 22.8% in the middle and late Miocene respectively. Both faunas point to the development of subtropical conditions in the area and match with the record of three new warming peaks. One hyperthermal event is recognized at the Middle Miocene Climatic Optimum, and the other two increments coincide with the transient peaks occurring at ~11 Ma and ~9 Ma. Paleogene-Neogene heritage in modern faunas of the region is rather poor and comprises 36% of fossil survivor genera. Taxa that managed to survive are mainly Cosmopolitan, Neogene Southern and Endemic genera that mostly had appeared in the early Miocene and adapted to Recent cool and temperate-cool conditions of the Southwesten Atlantic Ocean.

Natural and anthropogenic changes in the environment during the Holocene at the Kraków region (Southern Poland) from study of mollusc assemblages

Natural and anthropogenic changes in the environment during the Holocene at the Kraków region (Southern Poland) from study of mollusc assemblages

The invasive Asparagopsis taxiformis hosts a low diverse and less trophic structured molluscan assemblage compared with the native Ericaria brachycarpa

Invasive seaweeds threaten biodiversity and socio-economics values of worldwide marine ecosystems. Understanding to what extent invasive seaweeds can modify local biodiversity is one of the main priorities in conservation ecology. We compared the molluscan assemblage of the invasive Asparagopsis taxiformis with that of the native Ericaria brachycarpa and explore if variation in the molluscan assemblage diversity was related to the substrate attributes (biomass, and thallus, canopy, and interstitial volumes) of the algae. Results showed that A. taxiformis harboured lower diversity and trophic structure of the molluscan assemblage compared to E. brachycarpa. Biomass was the variable that better explained the variation of abundance and number of species as well as the multivariate structure of the molluscan assemblage. Overall, our results suggest that a complete habitat shift from native to invasive species can potentially trigger bottom-up effects in rocky shores habitats, reducing the biodiversity and the services provided by the invaded habitat.

Effects of habitat structure on the mollusc assemblage in Mussismilia corals: evaluation of the influence of different coral growth morphology

AbstractHabitat structure increases richness and abundance of species in many environments by providing easy access to resources and refuge from predators. In coral reefs, corals are habitat for many organisms and differences in their morphologies may act as variation in habitat structure for associated fauna. In the present study, we investigate whether there are differences in the richness and abundance of molluscs associated with three species of Mussismilia corals exhibiting different growth morphologies, in two different reef areas of the Bahia state. Mussismilia harttii has a meandroid pattern, M. hispida is a massive coral, M. braziliensis also has a massive growth pattern with crevices at the corallum base. Coral characteristics were measured in the laboratory. Significant differences were identified for richness among coral species – higher values were reported in colonies of M. harttii and no significant statistical differences were observed between M. braziliensis and M. hispida. Considering the density of associated molluscs, the same pattern was found. The results are in accordance with previous studies and indicate the importance of M. harttii as a key habitat to maintain a richer and more abundant associated fauna. The internal volume of interpolypal space is an important factor influencing the richness and density of associated species.

Protaspis larva of an aglaspidid-like arthropod from the Ordovician of Siberia and its habitat

A fossil larva lacking segmentation of the calcified carapace, closely resembling the trilobite protaspis, has been found associated with other skeletal elements of an angarocaridid Girardevia species in the mid Darriwilian of central Siberia. The presence of protaspis larvae in the angarocaridids, generally believed to represent a branch of the Aglaspidida, supports their proximity to trilobites and proves a low position on the arthropod phylogenetic tree but does not necessarily contradict the chelicerate affinity. The cephalic appendages of angarocaridids bore massive gnathobases with detachable spines, closely similar to those known in extant xiphosurans and in their probable Cambrian relatives. The stratigraphic succession of the angarocaridids, their phosphatized cuticle pieces being abundant in the Ordovician strata of Siberia, shows a gradual improvement of mechanical resistance of their carapaces, eventually resulting in a honeycomb structure. The associated benthic mollusc assemblage is dominated with the bellerophontids showing high mortality at metamorphosis and only the limpet-like Pterotheca, infaunal bivalves, and scaphopods being able to survive this in a substantial number. This suggests a strong selective pressure from predators equipped with well-skeletonised oral apparatuses able to crush mineralized body covers of their prey. Possibly, these were some of the associated conodonts of appropriate size and co-evolving towards their ability to crush more and more resistant cuticle. Less likely candidates for durophagy are endoceratid or orthoceratid cephalopods. Also the angarocaridids themselves, equipped with robust gnathobases of cephalic appendages, apparently predated on benthic shelly animals.

Decreasing in patch-size of Cystoseira forests reduces the diversity of their associated molluscan assemblage in Mediterranean rocky reefs

Canopy-forming seaweeds of the genus Cystoseira (Fucales, Phaeophyceae) form diverse and productive habitats along temperate rocky coasts of the Mediterranean Sea. During the last decade, Cystoseira forests have retracted their range considerably due to many interacting environmental, biological and anthropogenic pressures. We investigated how reducing in patch-size of C. montagnei affects their associated molluscan communities at the shallow northwest rocky shores of Palermo (Sicily, Italy). Molluscs were sampled from the fronds of individual thalli, clumps of 3 and 5 thalli of C. montagnei over an annual vegetative cycle (May–September) in two sites within the Marine Protected Area “Capo Gallo-Isola delle Femmine”. We measured five substrate attributes of the alga (thallus volume, canopy volume, interstitial volume, algal surface, and biomass) and explored their relationships with the diversity of the associated molluscan assemblage. A total of 3756 individuals of molluscs were collected, belonging to 30 families and 57 species, being Rissoidae the most speciose family and Barleeidae the dominant in terms of abundance. The molluscan assemblage on C. montagnei displayed significant spatial and seasonal variations, with the maximum number of individuals and species in summer, whereas evenness and diversity displayed maximum values in spring. The abundance, species richness and diversity of the molluscan assemblage decreased with decreasing in patch-size of C. montagnei, regardless of the vegetative phase of the alga or the sites considered in the study, while evenness showed an opposite trend. The substrate attributes of C. montagnei changed over the vegetative cycle of the alga and showed a similar pattern across sites with values that tended to decrease in autumn during the quiescence phase of the alga. Variation in patch-size of C. montagnei affected also the substrate attributes of the individual alga, with individual thalli becoming smaller with increasing patch-size. The algal surface of a single thallus of C. montagnei ranged on average from 956 cm2 in spring to 289 cm2 in autumn. Furthermore, algal surface together with thallus volume and dry weight were the substrate attributes that explained better the variation of the number of molluscan individuals and species. Overall, our results suggest that the reduction of both patch-size and algal substrate of C. montagnei forests altered the structure and composition of its associated molluscan assemblage. We argue that a reduction or loss of Cystoseira forests could probably trigger bottom-up effects in rocky shores habitats, with consequences for the whole ecosystem structure, functioning and services provided to humans.

Basin-wide infaunalisation of benthic soft-bottom communities driven by anthropogenic habitat degradation in the northern Adriatic Sea

Shallow coastal seas play an important role in the economy of many countries by sustaining fisheries, tourism, aquaculture and other economic activities. Their exploitation has large-scale ecosystem effects that are easily overlooked, as they often built up over decades or centuries, and historical ecological reference data are rarely available. Here, we assess these effects by comparing live and surface death assemblages (recording historical community states) of soft-bottom molluscs across a range of habitats in the northern Adriatic Sea, using the degree of mismatch between the 2 assemblages as a proxy for ecological change. We found a consistent live-dead mismatch at all stations. Although the degree of mismatch varied between stations with low and high time-averaging (i.e. the range of post-mortem shell ages), the community change followed the same trend over the entire Adriatic basin regardless of the type of sedimentary environment, with a loss of epifaunal species and the reduction of grazers, carnivores, and herbivores. In turn, the abundance of infaunal and opportunistic species feeding on plankton or detritus strongly increased in the living communities. Directionality and magnitude of these changes cannot be explained by time-averaging or by differences in species durability, but reflect a true ecological shift in response to multiple, long-lasting anthropogenic pressures, mainly bottom trawling, eutrophication and hypoxia. The original heterogeneous assemblages characteristic of different sedimentary habitats are thus replaced by a more infaunal, functionally impoverished and less diverse benthic community representing a new ecological baseline shaped by human impact.

Spatial Organization of the Micromollusc Community under Recreational Load

The recreational load is an important factor in transforming the living conditions of living organisms in the urban environment. This article examines the role of recreation as a driver of the changing habitat of soil micromolluscs in the park environment in an urban landscape. The hypothesis that recreational exposure changes the hierarchical organization of the spatial distribution of the micromollusc community was tested. An experimental polygon was located in Novooleksandrivskiy Park (Melitopol, Ukraine) and represented 7 transects with 18 test points in each. The set of soil properties explained 24.7% of the variation in the mollusc community. The distance from trees was able to explain 6.8% of mollusc community variation. The distance from recreational pathways was able to explain 12.2% of the variation in the mollusc community. The spatial eigenfunctions were able to explain 54.2% of mollusc community variation. The spatial patterns of variation in the structure of the assemblage of molluscs were found to be due to various causes. Thus, the broad-scale component was due to the distance from trees and the distance fro m the recreational pathways and was associated with the variability of soil penetration resistance, aggregate structure, electrical conductivity, soil moisture and density. The recreational load is the cause of this pattern formation. In turn, the medium-scale component reflected the influence of soil aggregate composition on the mollusс community and components independent of soil properties. The fine-scale component reflected the variability of the mollusc community, which was independent of soil properties.

Human- and climate-induced changes of mollusc assemblages of millpond deposits in the valley of Jarosławianka Stream (Poland)

Deposits from a millpond in the Jarosławianka Stream valley (Sławno Plain, NW. Poland) were subject to malacological analysis in order to reconstruct the history of environmental transformations of the pond from its establishment in 1351 to the end of its functioning in 1960. Thirty five mollusc taxa occurred in the pond during its functioning: 21 taxa of water snails, 11 bivalves, and 3 terrestrial snails. Six phases of development of the pond were distinguished, based on the mollusc assemblages: phase I (1351–1450 CE) – very favourable habitat conditions, high species richness and diversity; phase II (1450–1490 CE) – deterioration of habitat conditions – decrease in the number of species and individuals; phase III (1490–1590 CE) – improving conditions and reappearance of species which had occurred in the pond in phase I; phase IV (1590–1750 CE) – the least favourable conditions and poor malacofauna in terms of species number and abundance; phase V (1750–1790 CE) – renewed development of the malacofauna; phase VI (after 1790 CE) – end of functioning of the pond. The phases of pond development were associated with hydrological transformations, resulting from climatic factors and human economic activity.

Palaeoenvironmental conditions of the Palaeolithic–Neolithic transition in the Fergana Valley (Central Asia) – New data inferred from fossil mollusсs in Obishir-V rockshelter (Kyrgyzstan)

In the Fergana Valley and the surrounding territories, the number of archaeological sites increased during the Early Holocene. The coincidence of this cultural event, represented by the Obishirian archaeological unit with the onset of the Holocene, suggests that this growing intensity of human activity was driven by climate change, in particular warming and/or wetting. To test this hypothesis, we used fossil terrestrial molluscs from Obishir-V, the eponymic Obishirian site in southern Kyrgyzstan, as a proxy of palaeoenvironmental conditions. We studied pre-Obishirian loess-like deposits from the final Pleistocene and the Early–Middle Holocene sequence of Obishirian-bearing deposits. We analysed taxonomic composition of the mollusc assemblages and used it to infer palaeoecological characteristics, namely preferences in temperature and humidity as well as in differing habitats. Our results showed that the palaeolandscapes and the vegetation during the accumulation of the studied deposits remained almost unchanged. The mollusc assemblages reveal constant dry and warm climatic conditions and stable steppe-like vegetation. Our observations of rather stable climatic conditions in the Fergana Valley during the Pleistocene–Holocene turnover suggests that climate was only a minor driver of the rapid demographic change in Central Asia during those times. Some other factors beyond the changes of humidity must have played an important role. On the basis of our data derived from fossil mollusc assemblages at Obishir-V, we propose to consider the hypothesis that the factor responsible for the intense human occupation of the Fergana Valley during the Early Holocene had not an environmental, but rather a cultural background, such as the neolithization process, such as introduction of domestic livestock.

Cascading response of flora and terrestrial mollusks to last deglacial warming

The cascading impacts of climate-driven vegetation change on terrestrial invertebrates via trophic and habitat routes is a matter of outstanding concern. However, the combined responses of plant-animal associations in terrestrial ecosystems have seldom been reported on geological timescales, which raises the important questions of how frequently and to what extent such multi-trophic shifts in taxa have occurred during previous warming scenarios. Here we use a combination of mollusk, palynological, and climatic proxy evidence preserved within loess deposits in the southern Chinese Loess Plateau (CLP) to demonstrate how long-term changes in hydroclimatic dynamics during the past 26 kyr were reflected in the subsequent ecological changes. Specifically, there was a shift from a predominantly cold-tolerant mollusk fauna in a dry-steppe environment under cold-dry conditions during the last glacial, to a predominantly thermal-mesophilous fauna in a meadow-steppe environment under a warm temperate climate in the early-middle Holocene. Warmth-adapted mollusk species such as Opeas striatissimum and Punctum orphana were found to have been associated with several deciduous tree taxa (e.g., Corylus, Quercus, and Pterocarya) in both the Holocene record and in the modern ecosystem (based on surveys of 356 surface-soil plots). This suggests there is a clear ecological interdependency between specific vegetation types and mollusk assemblages. As such, the long-term vegetation-mollusk fossil records highlight the indirect impacts of climate change on terrestrial invertebrate turnover via plant-derived food structure and habitat routes, with major implications for understanding how these ecosystems are likely to respond to future climate changes.

Cenozoic Stratigraphy of the Eastern Part of the Opukha–Pekulney Depression, Koryak Upland, Northeast Russia

The Cenozoic marine deposits (two formations) developed in the eastern part of the Opukha–Pekulney Depression of the Koryak Upland are described. Until recently, there was scarce information about them. The lower (Retyrveem) formation is composed of dark conglomerates and sandstones with a large number of carbonate nodules and representative assemblages of bivalve and gastropod mollusks (more than 400 tests and imprints were studied) and Early Eocene benthic foraminifers. Two subformations and six units were distinguished in the formation. The upper (Morzhovaya) formation is composed of light loose gravestones and sandstones, including fragments of Early Miocene mollusks and foraminifers. The study of faunal assemblages makes it possible to correlate these formations with stratigraphic units of adjacent areas and to reveal hiatuses in the section covering most of the Paleocene sequence, on one hand, and the Upper Eocene and Oligocene, on the other hand. The Retyrveem Formation encloses warm-water molluscan assemblages, the appearance of which in the northern boreal latitudes is supposed to be related to the Early Eocene global warming. Images of the characteristic molluscan remains are given for the first time.

Low diversity or poorly explored? Mesophotic molluscs highlight undersampling in the Eastern Mediterranean

Mesophotic assemblages are the next frontier of marine exploration in the Mediterranean Sea. Located below recreational scuba diving depths, they are difficult to access but host a diverse array of habitats structured by large invertebrate species. The Eastern Mediterranean has been much less explored than the western part of the basin and its mesophotic habitats are virtually unknown. We here describe two mesophotic (77–92 m depth) molluscan assemblages at a rocky reef and on a soft substrate off northern Israel. We record 172 species, of which 43 (25%) are first records for Israel and increase its overall marine molluscan diversity by 7%. Only five of these species have been reported in recent surveys of the nearby Lebanon, suggesting that our results are robust at a broader scale than our study area and that the reported west-to-east declining diversity gradient in the Mediterranean needs a reappraisal based on proper sampling of the eastern basin. We found only four (2%) non-indigenous species, represented by seven (0.5%) specimens. These results suggest that pristine native assemblages still thrive at this depth in Israel, in contrast to the shallow subtidal heavily affected by global warming and biological invasions, calling for strong conservation actions for these valuable but vulnerable habitats.

Littoral vegetation predicts mollusc distribution in a network of unconnected small karstic lakes in the Mediterranean zone of Albania

AbstractSmall lakes and ponds in karstic systems have received little attention in terms of mollusc research. Although these systems represent a refuge for lentic biota in most of the Mediterranean, there are virtually no ecological studies from many regions, including Albania. Therefore, we quantitatively studied mollusc assemblages at 58 sampling sites within a compact karstic area of Central Albania and measured a set of potentially important environmental variables. Only nine ubiquitous species, including three non‐native mollusc species, were recorded. Gyraulus albus, Radix auricularia and Physa acuta were the most frequent species. Individual sites hosted notably species‐poor assemblages, ranging between zero and six species, with more than half of the studied sites being unoccupied. Mollusc presence was predicted mainly by fine substrate, depth of soft sediment and high transparency. Despite the importance of calcium for molluscs, more species were recorded at sites with a low calcium concentration. Regression tree analysis explained 40% of the total variation, defining reed cover and lake surface area as the most important variables for mollusc species richness. Based on mollusc species composition, the sites were clustered into four groups, differing mainly in submerged littoral vegetation cover, depth of soft sediment and reed cover. Our results showed that limited development of littoral vegetation and the area of lakes are the major drivers for mollusc species presence and their distribution in the studied network of unconnected karstic lakes.

Mollusks in the Stratigraphic Subdivision of the Cenozoic Key Section at Kvachina Bay, West Kamchatka

The characteristics of the mollusk assemblages in the Cenozoic key section at Kvachina Bay in West Kamchatka are given. Sixteen stratigraphically successive beds with mollusks, which are grouped in five horizons, are recognized in the sedimentary sequence with a total thickness of approximately 450 m. The biostratigraphic units are correlated with the regional horizons, and their age is determined in the interval of Middle Eocene–Middle Miocene. A number of specific features of the paleogeographic settings and climatic conditions are recognized.

Bathymetrical and temporal variations in soft-bottom molluscan assemblages in the coastal area facing the Sarno River mouth (Mediterranean Sea, Gulf of Naples)

Molluscan assemblage of coastal area facing the very polluted Sarno River estuary to offshore (Gulf of Naples, Italy) was studied, focusing on temporal and depth-related distribution of species diversity, quali-quantitative composition and trophic guilds structure. A total of 9 stations, at depths ranging between 7 and 95m, were sampled in triplicate by means of a 0.17 m 2 Van Veen grab in four sampling occasions (2 seasons, winter and summer, during 2 years, 2015 and 2016). A total of 1,744 individuals, belonging to 78 species and 3 classes (Bivalvia, Gastropoda and Scaphopoda), was recorded. Bivalves, followed by gastropods, qualitatively and quantitatively dominated the mollusc assemblages and both these taxonomic groups showed the highest values in the shallower stations down to about 25 m depth. In the deeper stations, only the bivalve taxon was dominant, even though exhibiting a much lower species richness and abundance. On the overall, the molluscan species were ascribed to 6 feeding guilds: Suspension and deposit feeders were the dominant trophic groups, occurring at all stations along the bathymetrical gradient, while predators, detritus feeders, ecto-parasites and scavengers were poorly represented and mainly occurred in the shallowest stations. The mollusc composition and distribution pattern along the bathymetrical gradient over time show signs of structural stability that might be mainly due to the continuous supply of organic matter from the river mouth expanding to all area. These results are of primary importance for filling the knowledge gaps on benthic biodiversity over a still poorly known and very fragile coastal area under continuous anthropogenic pressures mainly through the runoff of a very polluted river.