Microplastics (MP; 1 μm to 1 mm) of various shapes and compositions are ingested by numerous marine animals. Recently, proposals have been made to adopt bivalve molluscs as bioindicators of MP ...pollution. To serve as indicators of MP pollution, however, the proposed organisms should ingest, without bias, the majority of plastic particles to which they are exposed. To test this premise, eastern oysters, Crassostrea virginica, and blue mussels, Mytilus edulis, were offered variously sized polystyrene microspheres (diameters 19–1000 μm) and nylon microfibers (lengths 75–1075 × diameter 30 μm), and the proportion of each rejected in pseudofeces and egested in feces was determined. For both species, the proportion of microspheres rejected increased from ca. 10–30% for the smallest spheres to 98% for the largest spheres. A higher proportion of the largest microsphere was rejected compared with the longest microfiber, but similar proportions of microfibers were ingested regardless of length. Differential egestion of MP also occurred. As a result of particle selection, the number and types of MP found in the bivalve gut will depend upon the physical characteristics of the particles. Thus, bivalves will be poor bioindicators of MP pollution in the environment, and it is advised that other marine species be explored.
Summary
Benthic microeukaryotes are key ecosystem drivers in marine sandy beaches, an important and dynamic environment; however, little is known about their diversity and biogeography on a large ...spatial scale. Here, we investigated the community composition and geographical distributions of benthic microeukaryotes using high‐throughput sequencing of the 18S rRNA gene and quantified the contributions of environmental factors and spatial separation on the distribution patterns of both rare and abundant taxa. We collected 36 intertidal samples at 12 sandy beaches from four regions that spanned distances from 0.001 to 12,000 km. We found 12,890 operational taxonomic units (OTUs; 97% sequence identity level) including members of all eukaryotic super‐groups and several phyla of uncertain position. Arthropoda and Diatomeae dominated the sequence reads in abundance, but Ciliophora and Discoba were the most diverse groups across all samples. About one‐third of the OTUs could not be definitively classified at a similarity level of 80%, supporting the view that a large number of rare and minute marine species may have escaped previous characterization. We found generally similar geographical patterns for abundant and rare microeukaryotic sub‐communities, and both showed a significant distance–decay similarity trend. Variation partitioning showed that both rare and abundant sub‐communities exhibited a slightly stronger response to environmental factors than spatial (distance) factors. However, the abundant sub‐community was strongly correlated with variations in spatial, environmental and sediment grain size factors (66% of variance explained), but the rare assemblage was not (16%). This suggests that different or more complex mechanisms generate and maintain diversity in the rare biosphere in this habitat.
Suspension feeding bivalve molluscs interact with different types of microplastics (MP) suspended in the water column. Most bivalves are selective suspension feeders and, thus, do not consume all ...particles to which they are exposed. Selection depends upon the physicochemical properties and size of the particle. Recent work has provided evidence that blue mussels, Mytilus edulis, and eastern oysters, Crassostrea virginica, ingest and egest microspheres (polystyrene) and microfibers (nylon) differently, but whether other factors, such as polymer type and shape, mediate selection have not been explored. To investigate these factors, mussels and oysters were offered similar sized nylon (Ny) and polyester (PES) microfibers or polyethylene (PE) and polystyrene (PS) microspheres, or different sized PES microfibers during a 2 h exposure. Feces and pseudofeces were collected separately and analyzed for MPs, and the data were used to develop a linear regression model for selection. Results demonstrated clear species-specific differences in the efficiency of particle selection. Both mussels and oysters, however, exhibited size-based rejection of PES microfibers, ingesting a higher proportion of shorter fibers than longer fibers. Polymer type did not impact selection of fibers or spheres. The relative size of particles (area and perimeter) was found to be the most important factor in predicting whether a MP will be rejected or ingested.
Microplastics (MP) have repeatedly been found in commercially cultured species of bivalves. There are concerns regarding the amount of MP released into the environment by aquaculture activities, and ...questions regarding possible higher MP loads in farm-grown shellfish compared to levels in shellfish collected from recreational beds. To explore this concept, seawater, aquaculture gear, and eastern oysters (Crassostrea virginica) were sampled from an aquaculture site in Niantic Bay, CT, USA, and a 2-week transplantation experiment was performed in which oysters were transplanted between the aquaculture site and a plastic-free cage off the dock at the University of Connecticut-Avery Point campus. The digestive gland-stomach complex (gut) was dissected from the oysters and MP were extracted from the adjacent seawater and oyster gut samples using previously validated extraction methods. Extensive quality assurance and control measures were taken to reduce MP contamination. Particles in all samples were isolated, imaged under a stereomicroscope, and characterized (size, shape, polymer) using ImageJ software and micro-Fourier transform infrared spectroscopy. Water samples contained 0–0.3 MP/L and oyster gut samples contained 0–1.3 MP/g wet weight indicating very low concentrations of MP at the farm (0–2 MP/individual) or away from the farm (0–3 MP/individual). Aquaculture gear in this area is not contributing to MP ingestion in farmed oysters or elevated MP levels in the surrounding water.
•Microplastic concentrations were explored on an oyster aquaculture farm.•Oysters were transplant to or away from the aquaculture farm.•Microplastics in oyster-gut and seawater samples were compared to aquaculture gear.•Microplastic concentrations are low at and away from the farm in Long Island Sound.•Aquaculture gear did not contribute to microplastic ingestion in farmed oysters.
Ingestion of microplastics (MP) by suspension‐feeding bivalves has been well‐documented. However, it is unclear whether exposure to MP could damage the stomach and digestive gland (gut) of these ...animals, causing ramifications for organism and ecosystem health. Here, we show no apparent effects of nylon microfiber (MF) ingestion on the gut microbiome or digestive tissues of the blue mussel, Mytilus edulis. We exposed mussels to two low concentrations (50 and 100 particles/L) of either nylon MF or Spartina spp. particles (dried, ground marsh grass), ca. 250–500 μm in length, or a no particle control laboratory treatment for 21 days. Results showed that nylon MF, when aged in coarsely filtered seawater, developed a different microbial community than Spartina spp. particles and seawater, however, even after exposure to this different community, mussel gut microbial communities resisted disturbance from nylon MF. The microbial communities of experimental mussels clustered together in ordination and were similar in taxonomic composition and measures of alpha diversity. Additionally, there was no evidence of damage to gut tissues after ingestion of nylon MF or Spartina spp. Post‐ingestive particle processing likely mediated a short gut retention time of these relatively large particles, contributing to the negligible treatment effects.
Mussels were exposed to either nylon microfibers, a particle control, or non‐particle control for 21 days. Gut microbiomes showed resistance to disturbance from microbial biofilm communities, and gut tissues did not show damage from the ingestion of particles.
Microplastics (MP, <5 mm) are found in coastal waters across various environmental compartments (biota, water, marine snow, sediment). The eastern oyster (Crassostrea virginica) is a commercially ...important species that ingests MP; however, oysters are discriminant suspension feeders that do not consume all particles to which they are exposed. This study explored the relationship between MP in oysters on a recreational oyster bed and the surrounding environmental compartments in Long Island Sound (LIS; USA). The quantity and types of MP in oysters, water, marine snow, and sediment samples were determined. Precautions were taken to minimize and monitor MP contamination in the field and laboratory to improve the quality of data collected. Microplastics were isolated from samples via chemical digestion, and any suspected particles were identified using micro-Fourier transform infrared spectroscopy. A total of 86 MP were identified out of 885 suspected particles across environmental media. The highest MP count in an individual oyster was nine, indicating low concentrations of MP in oysters and the surrounding environment. Few polymers, except polyethylene terephthalate, were shared between oysters and the surrounding environmental compartments. Sediments contained the highest number of MP across all environmental compartments (42 total). These data aid in determining the types of MP (polymer composition, shape, size) to which oysters are exposed and identified those ingested. The low numbers of MP recorded, coupled with the lack of alignment of polymers between oysters and their surrounding environment, demonstrates further that oysters are a poor bioindicator species for MP pollution.
•Oysters are selective suspension feeders that do not consume all the particles they are exposed to.•Concentrations and polymers were explored and compared across oysters, water, marine snow, sediment on a recreational bed.•Microplastic concentrations are low and the polymers in oysters do not align with those in the surrounding environment.•These data indicates that oysters are a poor bioindicator species for microplastics pollution.
The capabilities of bivalve molluscs to feed selectively have been well documented, and physicochemical properties of particles have been implicated as possible factors in the selection process. In ...this study, the surface-property profiles of nine different microalgal species were determined by characterizing the surface charge, wettability (=contact angle), and surface carbohydrate moieties. Three fluorescein isothiocyanate (FITC) conjugated lectins were used to characterize carbohydrate moieties, including concanavalin A (ConA), Pisum sativum agglutinin (PEA), and wheat germ agglutinin (WGA). Distinct surface-property profiles were identified using linear discriminant analysis (DA) and used to design mixed-algal feeding experiments to assess particle selection by the blue mussel Mytilus edulis and the eastern oyster Crassostrea virginica. Results demonstrated preferential ingestion of some algal species over others, with strong rejection of some species (e.g. Pavlova lutheri and Prasinocladus marinus). These data were then used to develop DA and multiple linear regression models that considered the quantified surface properties and microalgal fates (rejected, ingested, or no selection) to examine determinants of selection. The DA model correctly classified 58% of the selection outcomes in mussels and 57% in oysters. Wettability was the most important factor in predicting selection in mussels, and surface charge was most important for oysters. In the multiple linear regression analyses, lectin affinity and wettability were the strongest predictors of particle selection, explaining ca. 90% of the variability in electivity index for mussels and 94% of the variability for oysters. By characterizing both physical and chemical surface properties of several microalgaeused as food for suspension-feeding bivalves, we demonstrate that multiple surface-property characteristics need to be considered in order to develop meaningful models of particle selection in bivalves. Future research also should take into account species-specific differences in selection.
•Surface properties of microalgae were characterized and used to develop particle selection assays for mussels and oysters•Results were modeled with microalgal surface characteristics to determine important predictors of particle selection•A discriminant analysis predicted selection 58% of the time in mussels, and 57% in oysters•Multiple regressions demonstrated microalgal-lectin affinity and wettability were the strongest predictors of selection•Regression models explained ca. 90% of the variability in electivity index for mussels and 94% for oysters
The microbial communities and overall health of the eastern oyster, Crassostrea virginica, have long been topics of interest due to the fundamental economic and ecological roles this species ...maintains. A broad scale characterization of the oyster microbiome over spatial and seasonal scales, however, has never been carried out. The primary goal of this study was to examine the factors mediating microbial communities of the gut and pallial fluid of C. virginica at three sites within the Long Island Sound estuary, with a focus on both genetic structure (T-RFLP) and physiological profiling (EcoPlates) of the microbiome. Results indicated that the genetic structure of microbial communities of oysters was minimally separated across sites, but was influenced by season. Although the microbial community structure was similar, the number of carbon sources utilized by these communities (richness) varied across site, season, and anatomical location within the host. Parameters including oyster condition index, Dermo disease, and ambient water temperature were measured to assess their influence on the oyster microbiome. Only water temperature was found to have a significant relationship with microbial community structure and richness. Results suggest that a core microbiome may exist within the eastern oyster, specifically for those populations that are not genetically distinct.
The blue mussel (Mytilus edulis) is a suspension feeder which has been used in gut‐microbiome surveys. Although raw 16S sequence data are often publicly available, unifying secondary analyses are ...lacking. The present work analysed raw data from seven projects conducted by one group over 7 years. Although each project had different motivations, experimental designs and conclusions, all selected samples were from the guts of M. edulis collected from a single location in Long Island Sound. The goal of this analysis was to determine which independent factors (e.g., collection date, depuration status) were responsible for governing composition and diversity in the gut microbiomes. Results indicated that whether mussels had undergone depuration, defined here as voidance of faeces in a controlled, no‐food period, was the primary factor that governed gut microbiome composition. Gut microbiomes from non‐depurated mussels were mixtures of resident and transient communities and were influenced by temporal factors. Resident communities from depurated mussels were influenced by the final food source and length of time host mussels were held under laboratory conditions. These findings reinforce the paradigm that gut microbiota are divided into resident and transient components and suggest that depuration status should be taken into consideration when designing and interpreting future experiments.
A multi‐study analysis of raw 16S gut microbiome data collected from blue mussels revealed that depuration strongly influences the recovered microbial community. When mussels were collected from the natural environment and sampled without depuration, the resulting gut microbiome was likely a mixture of both resident and transient microbes. When mussels were allowed to depurate and clear their digestive systems prior to sampling, the recovered gut microbiome was likely comprised of mostly resident microbiota.
One previously unstudied aspect of differences between sexual and asexual life stages in large‐scale transport and accumulation is density (mass per unit volume) of cells in each life stage. The ...specific density was determined for Scrippsiella lachrymosa cells in medium with and without nitrogen (N) enrichment through density‐gradient centrifugation. Growth medium without N addition is often called “encystment medium” when used for the purpose of resting cyst formation in cyst‐forming dinoflagellates; mating gametes are usually seen after 2–3 days. Significant differences in specific density were found after 2 days in encystment medium simultaneously with the observation of typical gamete swimming behavior and mating. The specific density of cells in encystment medium was 1.06 g · cm−3; whereas, the specific density of cells in growth medium was 1.11 g · cm−3. Cells in encystment medium were found to have significantly increased lipid content, reduced chlorophyll content, and reduced internal complexity. The findings may explain differential transport of less dense and chemotactically aggregating gametes into surface blooms in contrast to denser vegetative cells that perform daily vertical migration and do not aggregate. Passive accumulation of non‐migrating gametes into layers in stagnant water also can be explained, as well as sinking of zygotes when the storage of highly dense starch increases. Resting cysts had a density of over 1.14 g · cm−3 and would sink to become part of the silt fraction of the sediment. We suggest that differences in behavior and buoyancy between sexual and asexual life stages cause differences in cell accumulation, and therefore large‐scale, environmental transport could be directly dependent upon life‐cycle transitions.
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