Coastal Bivalves Research Articles

Efficient and reliable methods for estimating the abundance of keystone coastal macrofauna over large spatial scales.

Coastal bivalves are important ecosystem engineers, and identifying critical habitats can enhance conservation outcomes for threated keystone species as well as determining hotspots for invasive species. As early action is more efficient in both conservation and mitigation of species invasions, efficient and reliable tools for mapping and monitoring species over large scales are essential. We assessed the reliability and efficiency of towed video and quadrat sampling for estimating the abundance of three keystone macrofaunal bivalve species. To assess reliability, we compared the measured density based on each of the two methods to the "true" density estimated by manually surveying an entire transect. We found that both the video and quadrat method caused underestimation of the density of bivalves, but that the amount of underestimation was comparable, and further that both methods took substantially less time than surveying an entire transect manually. The video method underestimated the abundance of Pacific oysters (Magallana gigas), European flat oysters (Ostrea edulis), and blue mussels (Mytilus spp.) by 23%, 24%, and 16%, respectively. The causes of underestimation for the two oyster species were bivalves grouped in clusters, large amounts of small individuals, and generally higher abundances. While Mytilus spp. were underestimated overall, here observer experience was important, with inexperienced observers overestimating and experienced observers underestimating. Our study found both methods to be reliable and efficient for estimating the abundance of three keystone macrofaunal species, suggesting their potential applicability to other sessile or slow-moving species. We propose that these methods, due to their efficiency, can advance scientific knowledge and enhance conservation outcomes by establishing population baselines, assessing trends over time, and identifying and protecting critical habitats.

Organophosphate esters (OPEs) in the marine environment: Spatial distribution and profiles in French coastal bivalves

Organophosphate esters (OPEs), chemicals widely used in industrial production, electronics and domestic products, have become ubiquitous environmental contaminants. In this study, the levels and spatial distribution of 11 OPEs (aryl, alkyl and halogenated) were investigated in over 100 samples of filter-feeding bivalves collected yearly between 2014 and 2021 at sites of contrasted pressure along the French coasts. OPEs were found in virtually all samples, indicating their widespread spatial and temporal occurrence in coastal bivalves and the relevance of their biomonitoring. The median concentrations were between 0.4 (TMPP) and 4.9 ng g−1 dry weight (TCIPP), with TCIPP, TNBP and EHDPP found at the highest median values. TCEP and TBOEP were not frequently detected overall, but each year, the same sites showed repeatedly high concentrations. Structurally-related OPEs generally correlated, but the geographical distributions were not predictable from known anthropogenic pressures (population in the catchment area, industry), with little comparability with other hydrophobic contaminants. If the relation between sources of OPEs and bioaccumulated levels remains uncertain, local hotspots, rather than riverine/atmospheric transportation, could account for their geographical distribution. A systematic review of the levels of OPEs found in filter-feeding bivalves worldwide revealed comparable levels in our study with those reported elsewhere; however, the levels across and within (when available) studies generally spanned several orders of magnitude, indicating high spatial and temporal heterogeneity. In view of the growing concerns regarding OPEs, this study provides essential reference data for future studies of their occurrence on European coasts and supports the need for a more systematic (bio)monitoring of this class of contaminant.

Azaspiracid accumulation in Japanese coastal bivalves and ascidians fed with Azadinium poporum producing azaspiracid-2 as the dominant toxin component.

The filter-feeding bivalves often accumulate marine toxins by feeding on toxic dinoflagellates that produce marine toxins. Azaspiracids (AZAs) are a group of lipophilic polyether toxins which have been detected in a variety of organisms in many countries. In our present study, accumulation kinetics and toxin distributions in the tissues of seven bivalve species and ascidians relevant to Japanese coastal waters were investigated by experimentally feeding a toxic dinoflagellate Azadinium poporum, which produces azaspiracid-2 (AZA2) as the dominant toxin component. All bivalve species and ascidians investigated in this study had the capability to accumulate AZA2 and no metabolites of AZA2 were detected in the bivalves and the ascidians. Japanese short-neck clams, Japanese oysters, Pacific oysters and ascidians accumulated AZA2 with the highest concentrations on the hepatopancreas, whereas the highest concentrations of AZA2 were found on the gills in surf clams and horse clams. Hard clams and cockles accumulated high levels of AZA2 in both the hepatopancreas and the gills. As far as we know, this is the first report describing detailed tissue distribution of AZAs in several bivalve species other than mussels (M. edulis) and scallops (P. maximus). Variation of accumulation rates of AZA2 in Japanese short-neck clams on different cell densities or temperatures were observed.

Microplastic particles are phagocytosed in gill cells of deep-sea and coastal mussels

It is becoming obvious that the abundance of microplastics is increasing in worldwide oceans, raising concerns about their impact on marine ecosystems. Tiny plastic particles enter the body of marine organisms not only via oral ingestion but also through the body surface (e.g., gills or epidermis), but the mechanism of internalization into cells is poorly understood. In this study, we conducted experiments using deep-sea chemosynthetic mussels with limited feeding by exposing their gills to fluorescently labeled microplastic beads. We identified the gill cell types that preferentially internalized the beads and demonstrated the inhibitory effect of phagocytosis inhibitors on bead uptake. Furthermore, using correlative light-electron microscopy, we microhistologically verified that beads were enclosed within membrane-bound vacuoles. Our results indicated that microplastic particles were internalized into gill cells of deep-sea and coastal mussels by phagocytosis. This study highlights the need for further research on plastic contamination via the body surface to conserve the highly endemic and vulnerable deep-sea fauna and mitigate human health risks from consuming coastal bivalves.

Preliminary Studies on Species Diversity of Coastal Bivalves and the Traditional Knowledge on Bivalve Fishery in Sedili Kechil, Johor

Research on bivalves in Malaysia and documentation on bivalve fishery is still lacking in the recent years. Study on the diversity of bivalves will help contribute to the Malaysian database and the documentation of traditional knowledge on bivalve fishery will prevent the knowledge from going extinct. Therefore, this study was conducted to determine the species diversity of bivalves present in Sedili Kechil, Johor and also to gain access to the traditional knowledge of the fishermen involved in bivalve fishery practiced in the area. Bivalves were handpicked randomly throughout the coastal region and a total of 10 respondents make up the sample size of this study. The traditional knowledge was gathered with the aid of a semi-structured questionnaire through a combination of non-participant observation and in-depth interview method. This study has collected the first record of species of bivalves in Sedili Kechil. The bivalves’ diversity in Sedili Kechil is medium to low diversity by using Shannon Wiener Index (1.26) and Pielou’s Index of Evenness (0.41) and the traditional knowledge is documented regarding the variety of habitat preferences, fishery seasons, and exploitation and preservation methods. It is discovered that most bivalves occupy sandy substrates with four periods of availability and with different exploitation methods with respective to species. No preservation method is practiced by the villagers. The association with abiotic components and non-abiotic components and preference timing and depth for bivalve fishery are also noted. This record on species diversity and the documentation of traditional knowledge is hoped to be contributing to the Malaysian database and become preliminary data for future research.

The killer within: Endogenous bacteria accelerate oyster mortality during sustained anoxia

AbstractSustained periods of anoxia, driven by eutrophication, threaten coastal marine systems and can lead to mass mortalities of even resilient animals such as bivalves. While mortality rates under anoxia are well‐studied, the specific mechanism(s) of mortality are less clear. We used a suite of complementary techniques (LT50, histology, 16S rRNA amplicon sequencing, and valvometry) to show that the proliferation of anaerobic bacteria within eastern oysters (Crassostrea virginica) accelerates mortality rate under anoxic conditions. Manipulative laboratory experiments revealed that oyster survival under anoxic conditions was halved when bacteria were present compared to when they were excluded by the broad‐spectrum antibiotic chloramphenicol. Histological assessments supported this mechanism and showed infiltration of bacteria in oysters that were not treated with antibiotics compared to a general lack of bacteria when oysters were treated with antibiotics. 16S rRNA amplicon sequencing failed to identify any particular genera of bacteria responsible for mortality, rather a diversity of endogenous anaerobic and/or sulfate‐reducing bacteria were common among oysters. In addition, monitoring of oyster valve gaping behavior in the field revealed that oysters showed remarkable valve closure synchrony when first exposed to anoxia. However, oysters periodically opened throughout anoxia/hypoxia in both the lab and field, suggesting that the infiltration of exogenous bacteria from the environment may also influence mortality rates under natural settings. Coupled with previous studies, we posit that mass mortality events in a wide range of coastal bivalves are likely the result of co‐morbidity from asphyxiation and bacterial processes.

Does the environmental condition affect the tolerance of the bivalve Anomalocardia flexuosa to different intensities and durations of marine heatwaves?

Populations of the clam Anomalocardia flexuosa, subjected to different pollution conditions, were experimentally exposed to marine heatwaves of actual and future intensities and varying durations. We measured physiological and biochemical biomarkers and survival rates of the species under simulated heatwave events of 7 and 11 days. We observed that both the response of A. flexuosa to heatwaves and its baseline values of biomarkers were distinct between populations, demonstrating that the previous exposure to contaminants negatively interferes with the thermal tolerance of this bivalve. The duration and intensities of heatwaves here tested represent a considerable challenge for the survival of coastal bivalves. Our results suggest that the predicted increase in the ocean's average temperature and the frequency and intensity of marine heatwaves, as well as urbanization and increasing occupation of coastal regions, are factors that synergistically make A. flexuosa increasingly vulnerable over the decades.

Nationwide monitoring of microplastics in bivalves from the coastal environment of Korea.

Bivalves are useful bioindicators of microplastic contamination in the marine environment for several reasons, such as extensive filter feeding activity, broad geographical distribution, and limited movement capability. This study conducted a nationwide monitoring of microplastic pollution along the Korean coasts using filter-feeding bivalves (including oyster, mussel, and Manila clam) as bioindicators to identify the national contamination level and characteristics of microplastics. Seawater sample was collected from the same sampling stations of oyster and mussel for comparison. Microplastics were widely distributed in both coastal bivalves and waters with mean concentrations of 0.33±0.23 n/g (1.21±0.68 n/individual) in oyster/mussel, 0.43±0.32 n/g (2.19±1.20 n/individual) in Manila clam, and 1400±560 n/m3 in seawater. Despite the lack of significant relationship in the abundance of microplastics, their dominant features such as size, shape, color and polymer type were similar between bivalves and seawater. Fragments (69% for oyster/mussel, 72% for Manila clam, and 77% for seawater), particles smaller than 300μm (96% for oyster/mussel, 83% for Manila clam, and 84% for seawater) and colorless (79% for oyster/mussel, 85% for Manila clam, 75% for seawater) were the dominant shape, size and color, respectively. The major polymer types were polypropylene, polyethylene, and polyester. The microplastic level in bivalves was relatively high in urbanized areas with a wide diversity of polymer types compared with those in non-urbanized areas, and the proportion of polystyrene in the Korean samples was abundant compared with other regions due to wide use of polystyrene products in Korea. Our result suggests that microplastic contamination is widespread in the Korean coastal environment, and bivalves can reflect the microplastic pollution characteristics of the surrounding waters where they live.

In situ recovery of bivalve shell characteristics after temporary exposure to elevated pCO2.

Ocean uptake of carbon dioxide (CO2) is causing changes in carbonate chemistry that affect calcification in marine organisms. In coastal areas, this CO2-enriched seawater mixes with waters affected by seasonal degradation of organic material loaded externally from watersheds or produced as a response to nutrient enrichment. As a result, coastal bivalves often experience strong seasonal changes in carbonate chemistry. In some cases, these changes may resemble those experienced by aquacultured bivalves during translocation activities. We mimicked these changes by exposing juvenile hard clams (500 μm, Mercenaria mercenaria) to pCO2 in laboratory upwellers at levels resembling those already reported for northeastern US estuaries (mean upweller pCO2 = 773, 1274, and 1838 μatm) and then transplanting to three grow-out sites along an expected nutrient gradient in Narragansett Bay, RI (154 bags of 100 clams). Prior to the field grow-out, clams exposed to elevated pCO2 exhibited larger shells but lower dry weight per unit volume (dw/V). However, percent increase in dw/V was highest for this group during the 27-day field grow-out, suggesting that individuals with low dw/V after the laboratory treatment accelerated accumulation of dw/V when they were transferred to the bay. Treatments also appeared to affect shell mineral structure and condition of digestive diverticula. Although treatment effects diminished during the field grow-out, clams that were pre-exposed for several weeks to high pCO2 would likely have been temporarily vulnerable to predation or other factors that interact with shell integrity. This would be expected to reduce population recovery from short-term exposures to high pCO2.

Comprehensive monitoring of synthetic musk compounds from freshwater to coastal environments in Korea: With consideration of ecological concerns and bioaccumulation

This study investigated the concentration levels of synthetic musk compounds (SMCs), including HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-(g)-2-benzopyran), AHTN (7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene), MK (Musk ketone), and MX (Musk xylene), in freshwater, freshwater and coastal sediments, and coastal bivalves from freshwater to coastal environments. The levels in freshwater close to sewage treatment plants (STPs) showed higher contamination and suggested a medium to high ecological risk, especially posed by MK making more than 65% contribution to the combined risk by the total SMCs. STP effluent discharge points showed higher SMC concentrations in freshwater and coastal sediments. Predominant HHCB contributions regardless of sample types such as abiota and biota were consistent with the greater usage of HHCB than AHTN and MK in Korea. However, the higher contributions of AHTN than those predicted from AHTN consumption in Korea indicate the need for further research on the characteristic properties of individual SMCs, including partitioning, biomagnification, degradation, and metabolism for a realistic risk characterization. With respect to the highest HHCB levels in coastal bivalves reported, we determined the biota-sediment accumulation factor (BSAF) to understand the bioaccumulation of SMCs between coastal sediment and bivalves. The calculated BSAF values suggested that SMCs in bivalves were not biomagnified via the food chain but mostly partitioned from sediment. To our knowledge, this is the first study to measure BSAF values of SMCs, especially HHCB, AHTN, and MK, in coastal bivalve samples.

Diet and Daily Consumption Rates ofRapana venosa(Valenciennes, 1846) (Gastropoda: Muricidae) from the Río de la Plata (Argentina-Uruguay)

In this study we describe the feeding biology of the exotic predatory whelk Rapana venosa from the Río de la Plata when offered representative coastal bivalves from both soft and hard bottoms. Furthermore, we estimate daily consumption rates using two mussel species commonly found on local rocky outcrops and artificial reefs. R. venosa gastropods (n = 21; shell height (SH), 45–117 mm) were obtained by trawling in the Río de la Plata, and were kept in controlled laboratory settings. To describe its feeding behavior, 10 potential prey species were offered to the gastropods, including Mactra isabelleana, Erodona mactroides, Pitar rostratus, Donax hanleyanus, Mesodesma mactroides, Mytilus platensis, Brachidontes rodriguezi, Mytella charruana, Amiantis purpurata, and Crassostrea gigas. All prey species were consumed. The empty shells left after consumption frequently showed broken shells and rasp signatures on the edges, suggesting a prey attack by marginal chipping or a similar mechanism. This common pattern was not observed in A. purpurata or C. gigas. To explore potential effects of size on feeding behavior, the gastropods were separated into three size classes and offered M. platensis, B. rodriguezi, and M. charruana mussels. Small, intermediate, and large gastropods (SH <60 mm, 60–90 mm, and >90 mm, respectively) consumed comparable mussel size ranges. Small gastropods fed on prey sizes up to 30% larger than their size, whereas large gastropods consumed the largest mussel offered (SH, 78 mm). To estimate daily consumption rates, the 21 gastropods were fed with M. platensis and B. rodriguezi in individual tanks for 12 days. They ate 1.45 ± 0.67 SD mussels and 0.68 ± 0.65 g/day per gastropod. The proportion of tissue wet weight consumed did not change with prey species, but varied among the size classes of R. venosa. Small (<60 mm) and intermediate (60–90 mm) gastropods consumed a similar proportion of prey tissue (up to 12% of their tissue wet weight). In contrast, large gastropods (>90 mm) ate up to 5% of their tissue wet weight. This work is the first report of R. venosa feeding behavior and daily consumption rates in Argentina. The gastropods succeeded in attacking and feeding on a broad variety of local bivalve species characterized by noticeable differences in shell shape, size, and life habits.

Do organisms living around hydrothermal vent sites contain specific metallothioneins? The case of the genus Bathymodiolus (Bivalvia, Mytilidae)

The unusual characteristics of the hydrothermal vent environment (high pressure and metal concentrations, low pH, etc.) leads us to wonder how species living in this particular biotope have adjusted to these severe living conditions. To investigate the consequences of high metal concentrations, filter-feeding organisms are commonly used in ecotoxicological studies. Metallothioneins (MTs) are proteins conserved throughout the animal kingdom and involved in intracellular metal regulation Therefore, we tried here to find out whether the metallothioneins of hydrothermal bivalves are different from those of coastal bivalves. The characterization of DNA sequences coding MTs from some of the most common hydrothermal bivalves, belonging to the genus Bathymodiolus (Mytilidae) was performed by reverse transcription polymerase chain reactions (RT-PCRs). The complementary DNAs (cDNAs) of MT-10 and MT-20 isoforms were obtained for the Atlantic and Pacific hydrothermal mussels ( Bathymodiolus azoricus and Bathymodiolus thermophilus). The MT-10 transcripts were 222 nucleotides long and the MT-20 transcripts, 207 nucleotides. The polymorphism of the MT cDNAs in these two hydrothermal species is discussed. The comparison between metallothionein cDNA sequences of the Mytilus and the Bathymodiolus genera shows strong homologies among metallothioneins of coastal and hydrothermal mussels.