Mollusc Communities Research Articles

Mollusc community from a rocky intertidal zone in Acapulco, Mexico

The state of Guerrero, Mexico, has approximately 470 km of seashore but the marine fauna is not well known. The coastline has three marine areas for priority conservation of coastal and oceanic biodiversity, for which Comisión Nacional para la Conservación y Uso de la Biodiversidad (CONABIO) notes a distinct lack of knowledge in these areas. This study was carried out in a rocky intertidal middle zone from Playa ‘Majahua’, Acapulco, located south of Bahia de Puerto Marques. The objectives were to study: the species richness for classes Gastropoda, Bivalvia and Polyplacophora; the community structure from the representation of classes, families and genera; estimate density and species composition within a community; analyse size and structure of populations in the mollusc community; and estimate the diversity index. Three samplings were made in the intertidal middle zone in 2009. Ten square metres were sampled at each visit. Ninety-nine mollusc species were found to be represented, corresponding to 36 families. From all of these species, no record in Acapulco was found for 21 Gastropoda, 5 Bivalvia and 8 Polyplacophora species recorded. Gastropoda was the best represented; 1737 organisms were analysed with an estimated density of 86.8 organisms/m2 and 31 species were dominant. Crucibullum umbrella was the largest sized species. The diversity and equity index estimate in Majahua was the highest found for the rocky coast of Guerrero, indicating a mega-diverse area with great uniformity.

Dianchi Lake macroinvertebrate community succession trends and retrogressive analysis

Historical records and data from yield surveys conducted in 2009 and 2010 were used to investigate macroinvertebrate community succession trends in Dianchi Lake. Species richness has declined from 57 in the 1980s to 32 in 2010, representing a species loss of 44%. Among the major benthic groups, the highest rate of loss was recorded for mollusks (75%) and aquatic insects (39%). Surveys in 2009 and 2010 across the lake revealed that the total density was 1776 ind/m2, comprising oligochaetes (1706 ind/m2) and chironomids (68 ind/m2). Over a nearly twenty-year span (1992-2010), the density and biomass of oligochaetes first increased sharply (1992-2002) and then declined gradually (2002-2010). Further, chironomids have decreased gradually while the proportion of abundant species has increased. Limnodrilus hoffmeisteri became the sole dominant species with an average relative abundance of 74.1%. Cosmopolitan species, such as Einfeldia sp., disappeared across the lake; instead, tolerant species such as Chironomus plumosus, Ch. attenuatus and Tanypus chinensis became the common. Mollusk community structure has become simpler and many native species have gone extinct. Species of concern include Margarya melanioides, M. mondi, M. mansugi and Cipangopaludina dianchiensis, all rated as critically endangered by the IUCN. We found that the Shannon-Wiener index declined in Dianchi Lake, particularly in Caohai Lake, from 2.70 in the 1950s to 0.30 in 2009 and 2010. Species richness and biodiversity was significantly negative correlated with total phosphorus and total nitrogen. Factors responsible for the benthic community retrogression described here include habitat destruction, lowering of water quality, outbreaks of blue-green algae, extinction of submerged plants and lack of germplasm resources.

Molluscan communities in Vistulian loess located in Chobrzany, a village near Sandomierz (Southern Poland)

Malacological analysis was conducted on shell material from profile in Chobrzany village located near Sandomierz. This particular profile represents a vertical wall, up to 6.5 m high. Its upper part is composed of typical, yellow with vertical cracks covered by recent soil. In the lower interval the occurrence of poorly visible lamination and carbonate concretions is observed. Six species of snails were identified. These belong to the so-called loess species. Several types of molluscan communities can be distinguished on the basis of faunistic changes. These molluscs' assemblages correspond with the palaeoenvironment and they allow for palaeoclimatic and stratigraphical reconstructions. The results of malacological analysis indicate that the loesses in Chobrzany could belong to the youngest sequence (Upper Younger Loess), which were deposited during Pleniglacial Phase of Vistulian.

Mollusc communities in Bulgarian fens: predictive power of the environment, vegetation, and spatial structure in an isolated habitat

Mollusc communities of previously unexplored Bulgarian fens were studied in order to determine and generalise the patterns of species richness and composition along the mineral richness gradient. The aim was also to compare predictive values of the environment, vegetation and spatial structure. Altogether, 44 mollusc species were recorded at 40 treeless fen sites. Species richness varied from 0 to 18 species per site, and it was positively associated with the mineral gradient and negatively with altitude. However, the best predictor was obtained using plant species composition. All explanatory variables had higher effect on land snails than on the entire mollusc assemblage (including aquatic species). Species richness and abundance were significantly and positively correlated with the species composition turnover; the communities were highly nested, with poor sites having subsets of the fauna found in the richest. The main direction of mollusc species turnover was highly associated with that observed for vegetation, and the main gradient of plant species composition was able to explain nearly 20% of total variation in mollusc data. We found that spatial structure explained by far the highest proportion of independent variation, which reflected the high level of geographical isolation of Bulgarian fens and regional differences independent of any environmental variation. Our results demonstrate (1) the general role of mineral richness gradient for structuring mollusc communities in fens, (2) the pivotal indicator role of plant species composition in predicting species composition of mollusc communities, despite being trophically independent and (3) the effect of isolation and origins of the habitat on species composition: most species have wide geographical distributions within the habitat type, and geographical patterns within Bulgaria may have a stochastic element.

Mass mortality in Pacific oysters is associated with a specific gene expression signature

Mass mortality events occur in natural and cultured communities of bivalve molluscs. The Pacific oyster, Crassostrea gigas, is a dominant species in many intertidal locations as well as an important aquacultured bivalve species, and for the last 50 years, adult oysters have suffered frequent and extreme mass mortality events during summer months. To investigate the molecular changes that precede these mortality events, we employed a novel nonlethal sampling approach to collect haemolymph samples from individual oysters during the period that preceded a mortality event. Microarray-based gene expression screening of the collected haemolymph was used to identify a mortality gene expression signature that distinguished oysters that survived the mortality event from those individuals that died during the event. The signature was cross-validated by comparing two separate episodes of mortality. Here, we report that near-mortality oysters can be distinguished from longer-lived oysters by the elevated expression of genes associated with cell death, lysosomal proteolysis, and cellular assembly and organization. These results show the potential utility of nonlethal sampling approaches for investigating the environmental causes of mortality in natural populations in the field, and for predicting when such events could occur and which individuals will be affected.

A late Burdigalian bathyal mollusc fauna from the Vienna Basin (Slovakia)

A late Burdigalian bathyal mollusc fauna from the Vienna Basin (Slovakia)This is the first record of a bathyal mollusc fauna from the late Early Miocene of the Central Paratethys. The assemblage shows clear affinities to coeval faunas of the Turin Hills in the Mediterranean area and the Aquitaine Basin in France. The overall biostratigraphic value of the assemblage is hard to estimate due to the general very poor knowledge of Miocene bathyal faunas. Several species, however, are known from deep water deposits of the Middle Miocene Badenian stage as well. This implies Early Miocene roots of parts of the Middle Miocene deep water fauna and suggests a low turnover for bathyal mollusc communities at the Early-Middle Miocene boundary. The nassariid gastropodNassarius janschloegliHarzhauser nov. sp. and the naticid gastropodPolinices cerovaensisHarzhauser nov. sp. are introduced as new species.

Hydroseral habitat requirement of the endangered Shining Ramshorn Snail Segmentina nitida

Before the 1950s, the Shining Ramshorn snail Segmentina nitida was widespread across marshes and drainage ditches in Britain, continental Europe and Scandinavia. However, the population has declined rapidly and the IUCN Red Data list highlights the species as seriously vulnerable to extinction. It is now one of the six freshwater molluscan species protected under the UK Biodiversity Action Plan. Most previous research has focused on species decline and conservation issues. The aim of the research reported here was to clarify the habitat requirements of S. nitida in East Kent within the context of a seral classification. Six hydroseral stages were defined according to plant species composition. Segmentina nitida was limited uniquely to the Carex-Juncus-Eleocharis-Oenanthe community, a late seral stage in ditch succession, which confirms the work of other authors. A general linear statistical model applied to data from these sites suggested that (i) the total number of molluscs within each species varied across samples; (ii) the number of molluscs varied between samples with or without S. nitida; (iii) there was no variation in the total number of molluscs across the locations and (iv) there was no relationship between number of molluscs and sample site within location, implying some degree of connectivity between molluscan communities. Also a two-way ANOVA with Factor 1 as the number of mollusc and Factor 2 as the presence/absence of S. nitida showed a significant interaction effect. These observations are novel for these sites in East Kent and have implications for the ecology, life history strategy and conservation management of S. nitida.

Molluscan Community Composition and Richness in Four High-Elevation Idaho Streams Includes an Exotic Taxon

Abstract: Effective conservation requires that natural resource managers understand the diversity of organisms within a jurisdictional unit. Too frequently, conservation priorities are determined without adequate biological information, leading to inefficient use of very limited resources. We investigated molluscan community composition and richness within the eastern portion of the Sawtooth National Recreation Area (i.e., management unit) in Custer County, Idaho, USA to (1) identify populations of non-native species, if present, (2) acquire baseline information on the distribution, relative abundance, and diversity of molluscs in this high-elevation ecosystem, and (3) provide resource managers with useful information with which to inform conservation priority-setting. We found a rich molluscan community comprised of 19 species from 11 genera and 7 families. We also documented a single population of the non-native species Radix auricularia Linnaeus, 1758 from samples at Alturas Lake. Management of the ver...

Diversity of aquatic malacofauna of temporary water bodies within the lower Bug River floodplain

ABSTRACT: This study analyses the composition, species richness and diversity (H’) of aquatic molluscan communities in temporary water bodies within the valley of the lower Bug River in eastern Poland. The investigations were carried out in 2007–2009 within the section of the valley located between 190th and 50th km of the river course in 50 water bodies. Relatively rich and diverse malacofauna was found in the investigated habitats: 32 snail species and 6 bivalve species. Species diversity (H’) in individual water bodies ranged from 0.44 to 3.48. About 40% of all mollusc species showed frequencies of 10%. Dominance patterns varied much among the water bodies. Mollusc abundance ranged from 20 to over 1,800 indiv./m. Considerable species richness and diversity were found both within the active floodplain and the former one. This was probably related to the long duration of many of the investigated water bodies, as well as their periodical hydrological connectivity with permanent ones or river channel. From 9 to 12 samples should be enough to compile representative species list of molluscs inhabiting temporary water bodies, but as many as 28–40 samples would be necessary to obtain complete dataset.

Effect of eutrophication on molluscan community composition in the Lake Dianchi (China, Yunnan)

In this paper, three historical biodiversity datasets (from 1940s, 1980–1999 and 2000–2004) and results from the recent inventory are used to trace the long-term changes of the mollusks in the eutrophic Lake Dianchi. Comparison of the obtained results with those of earlier investigations performed during the period of 1940s and 1980–1999 as well as 2000–2004 showed that changes have occurred in the interval. There were 31 species and 2 sub-species recorded prior to the 1940s, but the species richness decreased from a high level of 83 species and 7 sub-species to 16 species and one sub-species from 1990s to the early of 21st century in lake body. Species from the genera of Kunmingia, Fenouilia, Paraprygula, Erhaia, Assiminea, Galba, Rhombuniopsis, Unionea and Aforpareysia were not found in Dianchi basin after 2000. The species from the genera Lithoglyphopsis, Tricula, Bithynia, Semisulcospira and Corbicula were only found in the springs and upstream rivers. Anoxia and the changing of substrates and fish species composition could explain why molluscan community composition changed in eutrophic Lake Dianchi. Additionally, the different sampling methods and ignore of the specific groups in earlier studies are cause for Sphaerium and Pisidium first found in our study. This study is first time to enlarge the investigation region to the Dianchi basin. Although some endemic species disappeared in the lake body, they still distribute in the springs and upstream rivers. The springs and upstream rivers are important refuges for mollusks.

Freshwater mollusc biodiversity and conservation in two stressed Mediterranean basins

This paper reviews the environmental factors that influence biodiversity of freshwater mollusc communities and conservation status of watercourses in two Mediterranean acid mine drainage-impacted basins of the southern Iberian Peninsula. We found 17 mollusc species: 14 gastropods (10 native and 4 introduced) and 3 bivalves. We found five distribution patterns: native headwater ( Arganiella wolfi , Stagnicola palustris , Unio delphinus , Pisidium casertanum and Pisidium personatum ) and mouth ( Hydrobia acuta , Peringia ulvae and Myosotella myosotis ) sensitive-stenochoric species, intermediate sensitive-widely distributed species ( Planorbarius metidjensis and Radix balthica ), insensitive-eurychoric species ( Ancylus fluviatilis ), and erratic-distribution pattern species ( Galba truncatula and Planorbis carinatus ). The highest biodiversity indices have been found in non-impacted headwaters and, to a lesser extent, in tidal streams. The biodiversity of the middle reaches, with varying degrees of impact by acid mine drainage and high water deficit, was scarce and dominated by introduced species. Over 30% of the variation in native and introduced species richness is explained by environmental gradients related to heterogeneity (instream macrophytes cover and Fhi and Qbr indices) and acid runoffs (pH, conductivity, turbidity and concentration of sulphides). Severely impacted sites have no mollusc species. The conservation status of watercourses is also very remarkably influenced by the heterogeneity and contamination of the environment. Conservation values are higher in water bodies located in protected northern and southern sites in both basins.

Long-term changes in mollusc communities of the Ognon river (France) over a 30-year period

The mollusc fauna of the Ognon river, one of the main tributaries of the Saone, surveyed for the fi rst time in 1977, was re-sampled in 2007 to assess long-term changes. Overall, the total number of collected individu- als increased by 33.6 % (55.2 % for gastropods and 23.7 % for bivalves) but total species richness remained stable during the period (40 vs. 39 species) although there was considerable species turnover: 8 disappearances offset by 7 appearances including that of the invasive Corbicula fl uminea which accounted for 30.4 % of the total number of individuals in 2007. The use of trend test, similarity index and principal component analyses (PCA) revealed radical changes in mollusc communities between years particularly in the upstream-downstream gradients of species rich- ness, total number of molluscs, and gastropods, bivalves, pulmonates, sphaeriid and unionid mussel densities. The upstream colonisation of several species was observed in the upper part of the river but in the lower part divergences in terms of species richness, density and structure increased in a downstream direction. The chronology of the changes observed strongly suggest that competition for food following the proliferation of C. fl uminea and the 2003 heatwave may be, responsible for the dramatic decline of native bivalves (Unionidae and Sphaeriidae, respectively). Given the magnitude of these changes, a return to a state prior to the disturbance of the malacological structure is hardly conceivable. However, the evolution towards a new relatively stable state is an alternative hypothesis.

Measures of taxonomic distinctness do not reliably assess anthropogenic impacts on intertidal mollusc communities

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 413:81-93 (2010) - DOI: https://doi.org/10.3354/meps08713 Measures of taxonomic distinctness do not reliably assess anthropogenic impacts on intertidal mollusc communities Trudy L. Costa1,2,3, Timothy D. O'Hara1,*, Michael J. Keough2 1Sciences Department, Museum Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia 2Department of Zoology, University of Melbourne, Victoria 3010, Australia 3Present address: School of Biological Sciences, University of Wollongong, New South Wales 2500, Australia *Corresponding author. Email: tohara@museum.vic.gov.au ABSTRACT: Indices of taxonomic distinctness measure the taxonomic breadth of a community and may be more sensitive to human impacts than conventional diversity indices. They have the advantage of being, in theory, insensitive to sampling effort and can be calculated using presence/absence data. The average taxonomic distinctness index and variation in taxonomic distinctness index were used to assess the effects of putative human impacts on molluscan community composition at 63 rocky intertidal platforms on the coast of Victoria, Australia. The use of 2 sampling techniques, viz. timed searches and quadrats, was compared. Sites exposed to sewage discharge maintained high taxonomic distinctness, and those exposed to high levels of human visitation did not have consistently lower values than controls. Results varied, sometimes markedly, depending on which survey technique was used. Neither average taxonomic distinctness nor its variance were strongly correlated with large-scale environmental gradients, small-scale habitat differences or other diversity indices. It is most likely that taxonomic distinctness measures did not discriminate sites exposed to putative disturbance because of the high taxonomic diversity of intertidal mollusc assemblages, and because low values of taxonomic distinctness were not exclusive of impacted conditions. KEY WORDS: Trampling · Sewage · Disturbance · TAXDTEST · Community composition · Invertebrate · Diversity Full text in pdf format PreviousNextCite this article as: Costa TL, O'Hara TD, Keough MJ (2010) Measures of taxonomic distinctness do not reliably assess anthropogenic impacts on intertidal mollusc communities. Mar Ecol Prog Ser 413:81-93. https://doi.org/10.3354/meps08713Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 413. Online publication date: August 26, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

GENDER DIFFERENCES AMONG SCHIZOPHRENIC PATIENTS ADMITTED TO THE PSYCHIATRIC EMERGENCY ROOM AND THE INSUFFICIENCE OF OUTPATIENT CARE IN BRAZIL

In this paper, three historical biodiversity datasets (from 1940s, 1980–1999 and 2000–2004) and results from the recent inventory are used to trace the long-term changes of the mollusks in the eutrophic Lake Dianchi. Comparison of the obtained results with those of earlier investigations performed during the period of 1940s and 1980–1999 as well as 2000–2004 showed that changes have occurred in the interval. There were 31 species and 2 sub-species recorded prior to the 1940s, but the species richness decreased from a high level of 83 species and 7 sub-species to 16 species and one sub-species from 1990s to the early of 21st century in lake body. Species from the genera of Kunmingia, Fenouilia, Paraprygula, Erhaia, Assiminea, Galba, Rhombuniopsis, Unionea and Aforpareysia were not found in Dianchi basin after 2000. The species from the genera Lithoglyphopsis, Tricula, Bithynia, Semisulcospira and Corbicula were only found in the springs and upstream rivers. Anoxia and the changing of substrates and fish species composition could explain why molluscan community composition changed in eutrophic Lake Dianchi. Additionally, the different sampling methods and ignore of the specific groups in earlier studies are cause for Sphaerium and Pisidium first found in our study. This study is first time to enlarge the investigation region to the Dianchi basin. Although some endemic species disappeared in the lake body, they still distribute in the springs and upstream rivers. The springs and upstream rivers are important refuges for mollusks.

Effect of hydrological connectivity on the molluscan community structure in oxbow lakes of the Łyna River

Abstract During 2004 and 2005 research on the malacocenoses existing in oxbow lakes differ in terms of hydrological connectivity was conducted in the valley of the Łyna River. The results showed that the connection of an oxbow lake with the river is the key factor influencing the abundance and biomass of molluscs in the lake. Three types of oxbow lakes representing lentic, semi-lotic and lotic environments were considered. In the lentic oxbow lake Mollusca was dominated by Potamapyrgus antipodarum Gray, the semi-lotic by Viviparus viviparus L., and the lotic by Pisidium sp. The most hospitable conditions for the molluscs' development were found in the semi-lotic reservoir where contact with the river was maintained by backwater in the downstream arm. The separation of the reservoir from the river caused a total reduction of the Bivalvia representatives. Diversity of the malacocenoses resulted mainly from different abilities to adapt to temporary oxygen deficits. Each type of oxbow lake is characterized by an individual pattern of oxygen distribution. To avoid anaerobic conditions and enable the development of biodiversity in floodplains, water bodies should be supplied by well-aerated river water.

Doplněk k poznání vodních měkkýšů Labe mezi Hřenskem a Střekovem a srovnání s malakofaunou Labe v jiných úsecích [A supplement to the knowledge on aquatic molluscs of the Elbe River between Hřensko and Střekov and a comparison with molluscan communities in other parts of the Elbe River (Czech Republic)

Doplněk k poznání vodních měkkýšů Labe mezi Hřenskem a Střekovem a srovnání s malakofaunou Labe v jiných úsecích [A supplement to the knowledge on aquatic molluscs of the Elbe River between Hřensko and Střekov and a comparison with molluscan communities in other parts of the Elbe River (Czech Republic)

Doplněk k poznání vodních měkkýšů Labe mezi Hřenskem a Střekovem a srovnání s malakofaunou Labe v jiných úsecích [A supplement to the knowledge on aquatic molluscs of the Elbe River between Hřensko and Střekov and a comparison with molluscan communities in other parts of the Elbe River (Czech Republic)

This paper completes knowledge on aquatic molluscs of the free flowing part of the Elbe River between Hřensko and the weir with lock in Ústí nad Labem – Střekov. Altogether, 21 species of aquatic molluscs (9 gastropods, 12 bivalves) were found in 2009. Viviparus viviparus, Potamopyrgus antipodarum, Bithynia tentaculata, Ancylus fluviatilis, Unio pictorum, Anodonta anatina, Corbicula fluminea, Sphaerium corneum and Pisidium supinum were the most frequently occurring molluscs found during this research. The occurrence of two endangered bivalves Pseudanodonta complanata and Pisidium moitessierianum was recorded. No significant difference from the previous author’s research was found. Molluscan communities of this part of the river were compared with those of the upper canalized part of the Elbe River which contain more species (especially gastropods) living predominantly in stagnant or slowly flowing waters e. g. Stagnicola palustris, S. corvus, Lymnaea stagnalis, Planorbis planorbis, Bathyomphalus contortus, Anisus vortex, Hippeutis complanatus, Ferrissia fragilis.

Oldest evidence of Acheulean occupation in the Upper Seine valley (France) from an MIS 11 tufa at La Celle

The tufa deposit of La Celle, located in the Upper Seine valley (Northern France), has been known for more than a century and extensive collections of shells and leaf impressions exist. These fossils led earlier authors to recognize the tufa as evidence of an old temperate phase of the Pleistocene. New studies have recently been undertaken at the site in order to reappraise its palaeontological potential and to improve its dating. Recent investigations are based on the analysis of a new series of stratified samples, coupled with a revision of material in several old collections. The new work shows that the tufa accumulated under interglacial conditions and demonstrates the progressive development of forest biotopes culminating in the climatic optimum. In the upper levels the reopening of the landscape is registered by both molluscan communities and plant remains. The tufa at La Celle has been correlated with MIS 11, based on the geomorphological context of the site, together with the occurrence of ‘the Lyrodiscus fauna’, a malacological assemblage characteristic of tufa deposits of this period in Northwest Europe. This correlation is supported by radiometric measurements (U-series and ESR/U-series,) which have produced a mean age of ∼400 ka. Mammalian remains are also preserved and include Macaca and Hippopotamus, which are the first well-provenanced records of these species from this region. An archaeological horizon with flint artefacts demonstrates human occupation during the interglacial optimum. Analysis of the lithic artefacts confirms their similarity with the Acheulean assemblage collected at the end of the 19th century. La Celle therefore represents one of the best dated Acheulean occupation sites in Northern France and one where the palaeoenvironmental context can be described in great detail.

Spatio-temporal and environmental gradient effects on mollusc communities in a unique wetland habitat (Turloughs)

Turloughs are karst wetlands unique to Ireland. We sought to elucidate mollusc community composition across a broad range of turloughs and to establish the major factors determining spatial distribution and community composition to better inform management decisions. Quantitative pond-net surveys for molluscs were conducted onCarex nigra dominated vegetation zones at each of eight turloughs. Surveys were conducted at each site twice — once just after flooding (early) and once before emptying (late). Thirteen other homogeneous zones were surveyed in the same way once, to assess relationships with environmental variables over the full hydrological gradient. The abundance of temporary-wetland specialists was significantly higher in the early as compared to the late samples, but late samples were more dissimilar to each other than early ones. Site was a more effective grouping variable than time of sampling for theCarex nigra community, and this effect was even higher when considering the whole hydrological gradient. The idiosyncratic nature of the turlough mollusc fauna was notable in both the indicator species analysis and the nestedness analysis. Results suggest a blanket approach to the conservation of turlough molluscan faunas is not appropriate and that turloughs should be considered individually when developing management recommendations.

Molluscan Community Recovery Following Partial Tidal Restoration of a New England Estuary, U.S.A.

Abstract Historic human‐imposed tidal flow restrictions at many New England estuaries have resulted in dramatic alteration of estuarine community structure and function. East Harbor, a 291‐ha coastal lagoon and salt marsh in Truro, Massachusetts, was artificially isolated from Cape Cod Bay in 1868. After the isolation, salinity decreased to near freshwater levels, and estuarine fish and invertebrate populations declined precipitously. Partial tidal flow was restored to East Harbor in 2002; since then, East Harbor has experienced substantial increases in salinity, and native fauna has begun to return to the system. The objective of this study was to obtain information on marine molluscan populations recolonizing East Harbor. Using a combination of benthic cores and direct searching, we surveyed 50 plots throughout the estuary in July and August 2005. We detected 16 molluscan species in East Harbor as a whole; the four most abundant species were Mya arenaria, Littorina spp., Mytilus edulis, and Mercenaria mercenaria. We found significant differences in species richness and abundance of these species among three regions of East Harbor that varied markedly in salinity and distance to Cape Cod Bay; diversity and abundance were both highest in Moon Pond, which has a direct connection with sources of seawater and marine biota, and lowest in the northwest cove, which receives high freshwater discharge. These findings demonstrate the effectiveness of Cape Cod National Seashore’s preliminary tidal restoration efforts while underscoring the continued need for full tidal restoration at East Harbor and other tide‐restricted estuaries.