Abundant Bivalves Research Articles

Variability in sediment-water carbonate chemistry and bivalve abundance after bivalve settlement in Long Island Sound, Milford, Connecticut

Cues that drive bivalve settlement and abundance in sediments are not well understood, but recent reports suggest that sediment carbonate chemistry may influence bivalve abundance. In 2013, we conducted field experiments to assess the relationship between porewater sediment carbonate chemistry (pH, alkalinity (At), dissolved inorganic carbon (DIC)), grain size, and bivalve abundance throughout the July–September settlement period at two sites in Long Island Sound (LIS), CT. Two dominate bivalves species were present during the study period Mya arenaria and Nucula spp. Akaike's linear information criterion models, indicated 29% of the total community abundance was predicted by grain size, salinity, and pH. When using 2 weeks of data during the period of peak bivalve settlement, pH and phosphate concentrations accounted 44% of total bivalve community composition and 71% of Nucula spp. abundance with pH, phosphate, and silica. These results suggest that sediment carbonate chemistry may influence bivalve abundance in LIS.

Population dynamics and secondary production of Darina solenoides (Bivalvia: Mactridae) in the Río Gallegos Estuary, southern Patagonia

The biology and ecology of Darina solenoides , an abundant bivalve of sandy sediments along Patagonian coasts, is poorly known. Here, we investigated the population dynamics and secondary production of this species in Rio Gallegos Estuary (Southern Patagonia, Argentina, 51°35’S, 69°01’W). Sampling was conducted monthly, from April 2014 to June 2015, by collecting 10 samples from the intertidal fringe using a core of 10 cm inner diameter. The sediment was mainly composed of fine and very fine (77.5%) sand; total organic matter content was 1.8%. The average population density was 779.4 ± 56.4 ind m -2 the population was composed of four modal groups. The settlement of a new cohort occurred in April-May each year. The von Bertalanffy growth function was L ∞ = 49.4 mm; K = 0.5; the calculated lifespan was 4.2 years. Population somatic production was 80.6 g dry mass m -2 yr -1 and the production-to-biomass (P/B) ratio was 0.96. The observed high production supports the hypothesis that D. solenoides is an important resource for many marine species.

Diversity of bivalves in Tanjung Balai Asahan Waters, North Sumatra, Indonesia

Susetya IE, Desrita, Ginting EDD, Fauzan M, Yusni E, Saridu SA. 2018. Diversity of bivalves in Tanjung Balai Asahan Waters, North Sumatra, Indonesia. Biodiversitas 19: 1147-1153. Local and regional market demands for bivalves increase outside Tanjung Balai City and Asahan District Waters, North Sumatra, Indonesia. As a result, high exploitation of bivalves occurred. In the other hand, there were less comprehensive information and studies on the diversity of bivalves in this area. This study aimed to determine the diversity of bivalves and water quality of Tanjung Balai Asahan Waters; was conducted between July 2016 and November 2017. Sampling of bivalves was conducted monthly. Several physical and chemical parameters were quantified. Data analysis included community structure analysis and Principal Component Analysis (PCA). The result showed that there were 16 species of bivalves from 7 families in Tanjung Balai Asahan Waters. Station 2 had the highest composition of bivalves, while the lowest was noted at Station 1. The mean abundance of bivalves at stations 1, 2 and 3 were 352±22 ind/m2, 222±14 ind/m2 and 388±30,2 ind/m2, respectively. In general, the index of diversity was categorized as low to moderate. The evenness index was categorized as low to high, while the dominance index indicated the absence of dominant species at almost all stations except station 1. Water quality of the waters was still in capacity to support the life of bivalves. Based on PCA analysis, it was obtained that the abundance of bivalves was positively correlated with nitrite, nitrate, phosphate, salinity, and pH.

Rapid assessment of the invasive Xenostrobus securis on cultured oysters in Hong Kong

The recently introduced bivalve Xenostrobus securis, which has established itself in the estuarine environments in Hong Kong, represents a potential threat to the local oyster aquaculture industry and native communities. Through a rapid assessment survey, the fouling bivalves on the cultured oyster Crassostrea hongkongensis were sampled along Deep Bay in February 2017. Six common fouling bivalves were identified in this survey, including the invasive X. securis, native Hiatella sp., Neotrapezium liratum, Arcuatula senhousia, Brachidontes variabilis and cryptogenic Perna viridis. Significant difference in bivalve assemblage was found between sampling sites along Deep Bay (p=0.0001). Across Deep Bay, X. securis was the most abundant fouling bivalve on C. hongkongensis (up to 3574 ind m−2), suggesting ecological advantages over native species. The sampled X. securis appeared to be comprised of juvenile individuals with an average shell length of 10.05 mm (± 1.96 SD). This study documents the first record of X. securis as a major fouling species on cultured oysters in Hong Kong. Although X. securis was the most abundant bivalve on cultured oysters in Deep Bay, its overall density was relatively low compared to other invaded regions. Therefore, we encourage the development of early response frameworks to monitor the population of X. securis and prevent potential economic and ecological losses in the area.

Small proportions of silt linked to distinct and predictable differences in marine macrofaunal assemblages on the continental shelf of the Pacific Northwest

Increasing interest in offshore development has motivated intensified efforts to map the seafloor for marine spatial planning. However, surficial geologic maps do not accurately represent habitats for various species groups of concern. This study used a bottom-up approach to integrate macrofaunal densities and benthic conditions on the Pacific Northwest shelf to identify macrofaunal assemblages and associated habitat features. Benthic cores and water-column profiles were collected from 137 stations from 50 to 110m depth. Analyses grouping stations based on both similar species abundances and benthic conditions resulted in six broad habitats. Within the sampled depth and latitudinal range, sediment characteristics were the primary structuring variable. A major break in assemblages was detected between sediment that had less than 1% silt/clay and those containing more than 1% silt/clay. Assemblages differed primarily in the bivalve species present and secondarily in polychaete species. Within the greater than and less than 1% silt/clay habitats, further discretization of assemblages was based mostly on differing abundances of characteristic bivalves and polychaetes associated with differing median grain sizes, which did not correspond to traditional definitions of fine or medium sand. These data show that a bottom-up methodology is necessary to discern habitats for macrofauna and that site-specific physical sampling is necessary to predict macrofaunal assemblage composition. However, if detailed sediment characteristics are known, macrofaunal assemblages may be predicted without time-intensive biological sampling and processing. These results also indicate that seemingly small sedimentary changes due to offshore installations may have measureable effects on the relative abundances and even the species composition of macrofauna.

Selection and Availability of Shellfish Prey for Invasive Green Crabs [Carcinus maenas(Linneaus, 1758)] in a Partially Restored Back-Barrier Salt Marsh Lagoon on Cape Cod, Massachusetts

ABSTRACT European green crabs (Carcinus maenas) are voracious, invasive predators of molluscs and their range is expanding throughout the northwest Atlantic Basin. Green crabs rapidly established following the 2002 partial restoration of East Harbor (EH) (42″039330 N, 70″079430 W), a back-barrier salt marsh lagoon within Cape Cod National Seashore, MA, where crabs potentially contribute to abrupt shifts in bivalve abundance and compromise restoration outcomes. Green crab prey preferences and effects on molluscan assemblages at this site have not been documented. Between June and September 2013, the prey selections of green crabs were documented using mesocosm feeding experiments and green crab diet through stomach content analyses. To evaluate prey availability, molluscan assemblage characteristics were also characterized using benthic coring. In the mesocosm experiments, green crabs strongly preferred large softshell clams [Mya arenaria (Linneaus, 1758)] and also chose small M. arenaria and Baltic clams ...

Feeding ecology of Limnoperna fortunei in southern China: insights from stable isotopes and fatty-acid biomarkers

ABSTRACTLimnoperna fortunei (L. fortunei) is one of the most abundant freshwater bivalves in southeast Asia, with wide-ranging direct and indirect impacts on ecosystems. To estimate material flows in the habitats of L. fortunei, a combination of stable-isotope and fatty-acid analyses were applied to assess the feeding spectrum of L. fortunei in southern China. Using the isotope-mixing model, the contribution proportions to the diet of L. fortunei were estimated as 19.8%–28.2% for plankton, 57.6%–65.2% for particulate organic matter (POM) and 10.2%–21.1% for sediment organic matter. We conclude that POM is the principal food source of L. fortunei. The δ13C enrichment of fixed carbon from POM to L. fortunei was 0.67%–2.41%. Based on the fatty acid data, it was estimated that L. fortunei consumed or selectively accumulated Chlorophyceae, Cryptophyceae, Dinophyceae, bacteria and terrestrial organic matter. The feeding spectrum of L. fortunei is similar to that of Dreissena polymorpha. We suggest that L. fortunei is able to differentiate suitable food items using chemical cues and the surface properties of particles.

Benthic Community Structure and Sediment Properties in Barnegat Bay, New Jersey, Before and After Hurricane Sandy

Hurricane Sandy was an extraordinarily large storm that affected most of the eastern coast of the USA in October 2012. To assess this storm’s impact, the benthic invertebrate community structure and sediment properties were compared in samples collected 3.5 months prior to (July 2012) and 8 months after (July 2013) the hurricane at 97 locations in Barnegat Bay, New Jersey, USA. Barnegat Bay is a shallow back-barrier estuary just north of where Sandy made landfall. For all locations taken together, sediment total nitrogen concentration was lower afterwards, while total organic carbon and total phosphorus concentrations were similar. Sediment median particle size was the same before and after, but the sediment was better sorted after the storm. There were no differences in total abundance of invertebrates, species richness, species diversity, or the abundance of polychaetes, bivalves, or gastropods. Malacostracan crustaceans were more abundant after Sandy (average 82 (0.04 m2)−1) than they were before (average 64), due almost entirely to increased abundance of ampeliscid amphipods, which showed a shift toward smaller sizes in 2013. Annelids in the order Clitellata were on average less abundant after the hurricane (17) than before (53). The apparent minimal effect of Sandy on the benthic community in Barnegat Bay was probably because the passage of the hurricane had no detectable effects on salinity or dissolved oxygen concentrations throughout the bay.

Molluscan Fauna in Bang Taboon Mangrove Estuary, Inner Gulf of Thailand: Implications for conservation and sustainable use of coastal resources

Molluscan fauna, dealt with diversity and abundance of gastropods and bivalves in Bang Taboon mangrove estuary, Inner Gulf of Thailand was investigated seasonally. Totally 3,337 individuals, representing 18 species (6 bivalves and 12 gastropods) with two dominant species, Assiminea brevicula and Tegillarca granosa . The mean density of overall molluscs was 11.79±0.47 n/m 2 , recorded in September. The highest value of diversity was 0.78±0.53, recorded in March. The most species-rich and individuals were recorded in the large mudflat within intertidal mangrove zone and formed a distinct community structure in the vegetated area at 15 cm depth. Results from the Analysis of the Similarity (ANOSIM) showed a clearly significant difference of species diversity and abundance at different areas, depths and seasons (P = 0.001). Although Bang Taboon estuary is impacted by human activities, the habitat remains an important nursery ground for numerous molluscs including many commercial species. The findings of this study can be taken as a base data that would help maximizing mangrove and fisheries resources conservation and utilization in a sustainable way in Bang Taboon estuary and adjacent areas in the inner Gulf of Thailand.

Ecological drivers and habitat associations of estuarine bivalves

Community composition of the infaunal bivalve fauna of the St. Lucie Estuary and southern Indian River Lagoon, eastern Florida was sampled quarterly for 10 years as part of a long-term benthic monitoring program. A total of 38,514 bivalves of 137 taxa were collected and identified. We utilized this data, along with sediment samples and environmental measurements gathered concurrently, to assess the community composition, distribution, and ecological drivers of the infaunal bivalves of this estuary system. Salinity had the strongest influence on bivalve assemblage across the 15 sites, superseding the influences of sediment type, water turbidity, temperature and other environmental parameters. The greatest diversity was found in higher salinity euhaline sites, while the greatest abundance of individual bivalves was found in medium salinity mixohaline sites, the lowest diversity and abundances were found in the low salinity oligohaline sites, demonstrating a strong positive association between salinity and diversity/abundance. Water management decisions for the estuary should incorporate understanding of the role of salinity on bivalve diversity, abundance, and ecosystem function.

Aspectos biológicos básicos de <i>Pinctada imbricata</i> (Bivalvia: Pteriidae) en la laguna de La Restinga, isla de Margarita, Venezuela

Pearl oysters are abundant bivalves in the northeastern coast of South America that form dense shoals in the Caribbean Sea, where they are exploited for marketing, making them a valuable resource in northeastern Venezuela. In order to provide information on Pinctada imbricata in the La Restinga Lagoon, its growth, size structure, condition index and natural mortality were estimated from April 2012 to January 2013. A total of 40 random samples of pearl oysters were collected on a monthly basis by freediving in a linear transect of approximately 200 m. The total length and total weight ratio indicated a negative allometric growth. A multimodal distribution was shown in almost all sampling months, with sizes ranging between 21.56 and 54.61 mm of total length. The modal peak observed in most of the months was between 24 and 28 mm, indicating a continuous recruitment throughout the year. The maximum peak of the monthly condition index was in May 2012, while the minimum was in November 2012. Growth parameters were L∞ = 68.5 mm, K = 1.18/year and t0 = 0.37, reaching the regulatory market size of 50 mm at approximately 18 months, with an estimated 2.92 year maximum longevity. Total mortality, corresponding to natural mortality M, was calculated as Z = 1.40/year.

A new Permian bivalve-dominated assemblage in the Rio do Rasto Formation, Paraná Basin, Brazil: Faunal turnover driven by regional-scale environmental changes in a vast epeiric sea

The basal portion of the Permian Rio do Rasto Formation (Serrinha Member), Passa Dois Group, Paraná Basin, Brazil, records an entirely new bivalve fauna intercalated between the underlying Pinzonella neotropica assemblage (uppermost portion of the Teresina Formation) and the overlying Leinzia similis assemblage (Rio do Rasto Formation). Mollusks of these assemblages lived in marginal shallow-water habitats of an immense epeiric sea and were dominated by endemic bivalve species. Taxonomic analysis revealed the presence of Terraia curvata (60.61%), Astartellopsis prosoclina (19.70%), Cowperesia emerita (10.61%), Leinzia curta (4.55%), Terraia bipleura (3.03%) and Beurlenella elongatella (1.52%), which are associated with conchostracans and plant remains. Species composition, abundance, and dominance in this novel assemblage differ notably from the preceding ones, suggesting a substantial evolutionary turnover. Regional-scale environmental changes recognized based on taphonomy, facies analysis, and geochemical data consist of progressive freshening of the marginal habitats of the Paraná Basin and taxic changes that include the following: (a) loss of genera, (b) decrease in bivalve abundance and ecological guilds, (c) disappearance of the dominant bivalve group (Pinzonellinae) and (d) diversification of Terrainae bivalves. The ecological signature also changed notably because only infaunal suspension-feeding bivalves are present, indicating a significant loss of functional diversity at the regional scale. Likely stressor factors (among others) are tied to freshening events, suggesting profound changes in (a) salinity, (b) primary productivity and (c) a lack of coarse, stable substrates coupled with high bioturbation rates. Hence, our regional example could offer valuable clues to benthic (bivalve) community responses in a habitat subjected to (a) rapid climate changes and (b) freshening events in shallow-water settings. Finally, the stratigraphic range of the dominant species (T. curvata) appears to be restricted to the basal portion of the Rio do Rasto Formation. Based on the presence of this species and of C. emerita, the novel assemblage is tentatively correlated with that of the Permian Gai-As Formation in the Huab region of Namibia, thus supporting previous assumptions of a seaway connecting both basins during the Guadalupian Epoch.

Zooplankton recolonization of the inner estuary of Bilbao: influence of pollution abatement, climate and non-indigenous species

Variations in mesozooplankton abundance and community structure in response to water quality improvement and to variations in hydro-climatic conditions were studied in the inner estuary of Bilbao from 1998 to 2011. A process of recolonization was observed with a marked increase in copepod abundance and a smaller increase in the abundances of appendicularians, meroplanktonic bivalves and gastropods, at the expense of the decrease in groups of gelatinous predators. Within the copepods, an initial phase in this recolonization occurred through an increase in neritic copepods. However, in a second phase, the non-indigenous species Acartia tonsa and Oithona davisae increased and became dominant. In the last 2 years, a third non-indigenous species Pseudodiaptomus marinus was observed in lower densities, and Calanipeda aquaedulcis abundance increased becoming co-dominant with A. tonsa. All non-indigenous copepod species had summer/autumn peaks and were characteristic of brackish conditions, which suggests that unsaturated ecological niches in brackish waters were important for the settlement of non-indigenous species. Pollution abatement allowed for zooplankton recolonization, but variations in community structure, both at the broad taxonomic group and at the copepod species level, were greatly influenced by hydro-climatic factors, temperature being the single best explanatory variable of zooplankton variations.

Invasive prey indirectly increase predation on their native competitors.

Ecological theory predicts that invasive prey can interact with native prey directly by competing for shared resources or indirectly by changing the abundance or behavior of shared native predators. However, both the study and management of invasive prey have historically overlooked indirect effects. In southern California estuaries, introduction of the Asian nest mussel Arcuatula senhousia has been linked to profound changes in native bivalve assemblages, but the mechanisms of these interactions remain unclear. We performed three field experiments to assess the mechanisms of competition between Arcuatula and native bivalves, and evaluated the potential for Arcuatula to indirectly mediate native predator-prey dynamics. We found that Arcuatula reduces the diversity, abundance, and size of native bivalve recruits by preemptively exploiting space in surface sediments. When paired with native shallow-dwelling clams (Chione undatella and Laevicardium substriatum), Arcuatula reduces adult survival through overgrowth competition. However, Arcuatula also attracts native predators, causing apparent competition by indirectly increasing predation of native clams, especially for poorly defended species. Therefore, invasive prey can indirectly increase predation rates on native competitors by changing the behavior of shared native predators, but the magnitude of apparent competition strongly depends on the vulnerability of natives to predation. Interestingly, our results indicate that the vulnerability of invasive prey to predation can greatly exacerbate impacts on their native competitors. Our findings suggest that consideration of both direct and indirect effects of invasive prey, as well as native predator-prey relationships, should lead to more effective invasive species management.

Species-specific effects of seagrass on belowground biomass, redox potential and Pillucina vietnamica (Lucinidae)

The network of roots and rhizomes of seagrasses plays an important role in coastal ecosystems by anchoring the substrate firmly, controlling the biogeochemistry of the sediments and providing habitat for many infaunal organisms. The purpose of this study was to compare five seagrass communities in southern Thailand in terms of species composition, belowground biomass, redox potential and the abundance of the dominant bivalve Pillucina vietnamica. The communities of Halophila ovalis, Cymodocea rotundata, Thalassia hemprichii, H. ovalis with C. rotundata and C. rotundata with T. hemprichii were studied. Belowground biomass, redox potential, bivalve abundance and bivalve size differed among communities and depths (P < 0.05). The redox potential in vegetated areas was lower than in bare sand, showing that seagrass roots trapped more organic matter than did bare sand. The lowest redox potential was in a monospecific patch of the branching root species, C. rotundata. The abundance of P. vietnamica in vegetated areas was lower than in bare sand (P < 0.05). Pillucina vietnamica was relatively large in size in the monospecific stands of C. rotundata and T. hemprichii, where relatively high root biomass and belowground biomass, respectively, were found. Our results suggest that seagrass promotes anoxic conditions belowground by trapping sediment but could obstruct the burrowing activity of lucinids, as dense populations of lucinids occurred mainly in bare sand. However, seagrass also provided shelter for lucinids, as larger bivalves were found in seagrass areas. The interactions among belowground seagrass parts, the biogeochemistry of sediments and the lucinids are highly complex and merit further study.

Distribution, Abundance, and Habitat Associations of a Large Bivalve (Panopea generosa) in a Eutrophic Fjord Estuary

ABSTRACT Marine bivalves are important ecosystem constituents and frequently support valuable fisheries. In many nearshore areas, human disturbance—including declining habitat and water quality—can affect the distribution and abundance of bivalve populations, and complicate ecosystem and fishery management assessments. Infaunal bivalves, in particular, are frequently cryptic and difficult to detect; thus, assessing potential impacts on their populations requires suitable, scalable methods for estimating abundance and distribution. In this study, population size of a common benthic bivalve (the geoduck Panopea generosa) is estimated with a Bayesian habitat-based model fit to scuba and tethered camera data in Hood Canal, a fjord basin in Washington state. Densities declined more than two orders of magnitude along a north—south gradient, concomitant with patterns of deepwater dissolved oxygen, and intensity and duration of seasonal hypoxia. Across the basin, geoducks were most abundant in loose, unconsolidat...

Ecological consequences of the Guadalupian extinction and its role in the brachiopod-mollusk transition

AbstractThe Guadalupian (middle Permian) extinction may have triggered substantial ecological restructuring in level-bottom communities, such as turnover in dominant brachiopod genera or a shift from abundant brachiopods to mollusks, despite comparatively minor taxonomic losses. However, ecological changes in relative abundance have been inferred from limited data; as a result, constraints on important shifts like the brachiopod-mollusk transition are imprecise. Here, I reevaluate the magnitude of ecological shifts during the Guadalupian–Lopingian (G-L) interval by supplementing previous census counts of silicified assemblages with counts from non-silicified assemblages and global occurrence data, both sourced from the Paleobiology Database. Brachiopod occurrences are consistent with more pronounced faunal composition changes from the Guadalupian to Lopingian than among stages within those intervals, but only in Iran and South China, and not in Pakistan or a Tethys-wide data set. In Iran and South China, Bray-Curtis dissimilarity values comparing occurrence frequencies between adjacent stages were elevated across the G-L transition, although other intervals exhibited similarly large shifts. However, genus occurrence frequencies were less strongly correlated or were anti-correlated across the G-L transition, suggesting moderate faunal turnover among dominant brachiopod genera. In contrast to previous inferences from silicified faunas, abundances of brachiopods, bivalves, and gastropods remained consistent from the Guadalupian to Lopingian in non-silicified local counts and global occurrences, implying that the brachiopod-mollusk shift did not occur until the end-Permian extinction. Ecological and taxonomic consequences were both minor in level-bottom settings, suggesting that severe environmental perturbations may not be necessary to explain biotic changes during the Guadalupian-Lopingian transition.

Responses of stream benthic macroinvertebrate communities to timber harvesting: Best management practices in a low-gradient watershed in Central Louisiana, USA

AbstractForests are the most dominant land-use type in Louisiana, and timber harvesting is the most economically important of the state’s agricultural commodities. Louisiana has developed voluntary best management practices (BMPs) to minimize negative effects of forest operations on stream water quality, but little is known about how aquatic communities inhabiting low-gradient, headwater streams respond to timber harvesting, and if the current BMPs are effective in protecting community structure and function. In 2005, we initiated a multidisciplinary study in the Flat Creek watershed in central Louisiana to discern the effects of timber harvesting activities, with and without BMP implementation, on benthic aquatic macroinvertebrates. During fall 2007, trees were removed adjacent to two headwater streams in the watershed, and benthic macroinvertebrate samples were subsequently collected at seven stream locations seven times between 2006 and 2009. Our objectives were to describe the community structure of benthic macroinvertebrates in low-order, low-gradient streams, how macroinvertebrate communities responded to timber harvest operations, and whether significant changes in community structure were evident under different levels of BMP implementation. The community structure was predominantly generalist taxa including chironomids, sphaeriid bivalves and asellid isopods. Analyses of variance demonstrated significant increases in bivalve abundance and decreases in the abundance of malacostracan and shredding taxa at most of the sampling sites downstream of BMP-implemented harvest locations in the spring. Additionally, significant increases in bivalves were also found at two sites during late summer. Our results suggest that timber harvesting activities, regardless of BMP implementation, had limited shortterm impacts on resident macroinvertebrates in these lowgradient, subtropical streams. Continued monitoring at the study sites will allow us to better understand the longterm effects of timber harvesting in these stream systems, particularly the resilience of stream biota to harvestingrelated stream conditions.

Changes in macrozoobenthic assemblages in a shallow subtropical lake (Lake Taihu, China): 1987–1988 vs. 2007

Lake Taihu is subject to severe eutrophication due to high nutrient inputs. We compared the macrozoobenthic assemblages of Lake Taihu in 1987–1988 and in 2007. Changes in benthic communities between the two periods were significantly different among the four lake regions (the River Mouth, the North Bay, the Open Lake, and the East Bay), corresponding well with the changed environmental conditions. The River Mouth and North Bay showed the greatest changes in benthic fauna, corresponding with severe degradation in water quality. In 1987–1988, benthic communities were dominated by Tubificidae and Bivalvia in the River Mouth and the North Bay, respectively. In 2007, however, benthic fauna were mainly dominated by Tubificidae in the North Bay and total macrozoobenthos increased approximately 18-fold in abundance. The Open Lake was dominated by bivalves (mainly Corbicula fluminea) in both sampling periods, whereas an increased abundance of bivalve was observed from 1987–1988 to 2007. In the East Bay, which was covered by abundant macrophytes, the macrozoobenthos community decreased in abundance and was characterized by high species richness of gastropods. In addition, the abundance of gastropods, tubificids, and chironomids increased significantly between the two sampling periods. The relatively stable ecological conditions in the East Bay (e.g., trophic state and spatial distribution of macrophytes within the East Bay) might be responsible for the relatively small changes. Our results showed complex variation patterns of macrozoobenthic assemblages among different sections of Lake Taihu, which may be associated with the great environmental heterogeneity in this large shallow lake.

Bivalve and barnacle larvae distribution driven by water temperature in a Mediterranean lagoon.

The objective of this study was to explore the relationships between the distribution of some meroplanktonic species and water temperature. Meroplankton larvae abundance of bivalves, and barnacles and water temperature fluctuations were studied from February 2011 to January 2012 at five stations in Ghar El Melh lagoon (GML) Mediterranean Sea, northern Tunisia). According to redundancy analysis (RDA), a significant difference was found in the distribution of larvae among the seasons (F = 10.28, p < 0.001); summer and autumn appear to be the period of bivalve larvae development, whereas the arrival of barnacle larvae coincided with winter and spring. The generalized additive models (GAMs) show strong correlation of bivalve larvae with high temperature (F = 23.2; p < 0.001) and the affinity of barnacle larvae to low temperature values (F = 8.41; p = 0.004). This environmental parameter accounted for 26 % of the deviance in variability in larvae abundance. The development process of many generations of larvae may therefore have been predetermined by temperature.