The relative effects of interspecific and intraspecific diversity on microplastic trapping in coastal biogenic habitats

Intraspecific variations in oyster (Magallana gigas) ploidy does not affect physiological responses to microplastic pollution

Recent advances in genetic manipulation such as triploid breeding and artificial selection, have rapidly emerged as valuable hatchery methodologies for enhancing seafood stocks. The Pacific oyster Magallana gigas is a leading aquaculture species worldwide and key ecosystem engineer that has received particular attention in this field of science. In light of the growing recognition of the ecological effects of intraspecific variation, oyster polyploids provide a valuable opportunity to assess whether intraspecific diversity affects physiological responses to environmental stressors. While the responses of diploid and triploid oysters to climate change have been extensively investigated, research on their sensitivity to environmental pollution remains scarce. Here, we assess whether genotypic (i.e., ploidy) variation within Magallana gigas affects physiological responses to microplastic pollution. We show that diploid and triploid M. gigas have similar clearance rates and ingest similar amounts of microplastics under laboratory-controlled condition. In addition, they exhibited similar heart rates after prolonged exposure to microplastic leachates. Our findings suggest that intraspecific variations within M. gigas ploidy does not affect oyster responses to microplastic pollution. However, regardless of ploidy, our work highlights significant adverse effects of microplastic leachates on the heart rate of M. gigas and provides evidence of microplastic ingestion in the laboratory.

Microplastics associated with stranded macroalgae on an impacted estuarine beach, Rio de Janeiro, Brazil

Microplastics (MPs) are contaminants widely distributed in marine ecosystems. Only few studies approached MP interactions with marine plants, which are considered potential traps for MPs. Here, we determined MPs' densities and types associated with stranded macroalgae on a eutrophic beach in Guanabara Bay. Our results showed that red algae exhibited higher MP densities (1.48 MPs g-1), possibly due to their more branched thalli, than green algae (0.27 MPs g-1). The predominant MP types were blue and white fragments <3 mm in size and polymers were classified as polyethylene and polyvinyl chloride in fragments, and polypropylene in fibers. The higher densities of MPs in algae seemed to be influenced by the inner bay waters. The densities of MPs associated with algae from Guanabara Bay surpassed those reported in other studies. High MPs densities increase the chances that organisms associated with algae entangle or ingest MPs, impacting their health and survival.

Biomonitoring of microplastics, anthropogenic microfibres and glass retroreflective beads by marine macroalgae

Microplastics and other microscopic debris are a concern in the coastal environment but measurements in the water column and sediment are often problematic and rely on non-standardised and highly variable methodologies. To this end, we explore the potential of different species of temperate-cold marine macroalgae as passive biomonitors of anthropogenic microparticles at three contrasting locations in southwest England. Specifically, fronds from samples of fucoids and Ulva lactuca (n = 9 in total, and three from each location) have been sectioned and analysed directly under a microscope and anthropogenic microparticles counted and subsequently characterised for chemical composition. Microparticles were heterogeneously distributed throughout sections from the same sample. However, on a dry weight basis, combined microparticle concentrations for each sample ranged from about 7.5 g-1 to 110 g-1, and from about 0.2 cm-2 to 0.9 cm-2, and for a given species were higher in samples from a semi-enclosed harbour and urban beach than in samples from a protected beach facing the open sea. These values compare with published concentrations of microplastics and microfibres reported for the regional water column on the order of 0.1 m-3. Most particles were cellulosic (e.g., rayon) and petroleum-based (mainly polyester and polyethylene terephthalate) fibres but plastic fragments were also present on most samples. Glass retroreflective beads derived from road markings were also present at up to 18 g-1 on fucoids from the urban beach because of its proximity to a stormwater effluent. Most microparticles were adhered to the smooth parts of the macroalgal surface but some displayed wrapping around edges and creases or entrapment by appendages. The practical and environmental implications of macroalgae passively capturing significant quantities of anthropogenic microparticles are discussed.

Microplastic shape influences fate in vegetated wetlands

Coastal areas are prone to plastic accumulation due to their proximity to land based sources. Coastal vegetated habitats (e.g., seagrasses, saltmarshes, mangroves) provide a myriad of ecosystem functions, such as erosion protection, habitat refuge, and carbon storage. The biological and physical factors that underlie these functions may provide an additional benefit: trapping of marine microplastics. While microplastics occurrence in coastal vegetated sediments is well documented, there is conflicting evidence on whether the presence of vegetation enhances microplastics trapping relative to bare sites and the factors that influence microplastic trapping remain understudied. We investigated how vegetation structure and microplastic type influences trapping in a simulated coastal wetland. Through a flume experiment, we measured the efficiency of microplastic trapping in the presence of branched and grassy vegetation and tested an array of microplastics that differ in shape, size, and polymer. We observed that the presence of vegetation did not affect the number of microplastics trapped but did affect location of deposition. Microplastic shape, rather than polymer, was the dominant factor in determining whether microplastics were retained in the sediment or adhered to the vegetation canopy. Across the canopy, microfibre concentrations decreased from the leading edge to the interior which suggests that even on a small-scale, vegetation has a filtering effect. The outcome of this study enriches our understanding of coastal vegetation as a microplastics sink and that differences among microplastics informs where they are most likely to accumulate within a biogenic canopy.

Microplastic trapping efficiency and hydrodynamics in model coral reefs: A physical experimental investigation

Coastal ecosystems, such as coral reefs, are vulnerable to microplastic pollution input from proximal riverine and shoreline sources. However, deposition, retention, and transport processes are largely unevaluated, especially in relation to hydrodynamics. For the first time, we experimentally investigate the retention of biofilmed microplastic by branching 3D printed corals (staghorn coral Acropora genus) under various unidirectional flows (U = {0.15, 0.20, 0.25, 0.30} ms-1) and canopy densities (15 and 48 corals m-2). These variables are found to drive trapping efficiency, with 79-98% of microplastics retained in coral canopies across the experimental duration at high flow velocities (U = 0.25-0.30 ms-1), compared to 10-13% for the bare bed, with denser canopies retaining only 15% more microplastics than the sparse canopy at highest flow conditions (U = 0.30 ms-1). Three fundamental trapping mechanisms were identified: (a) particle interception, (b) settlement on branches or within coral, and (c) accumulation in the downstream wake region of the coral. Corresponding hydrodynamics reveal that microplastic retention and spatial distribution is modulated by the energy-dissipative effects of corals due to flow-structure interactions reducing in-canopy velocities and generating localised turbulence. The wider ecological implications for coral systems are discussed in light of the findings, particularly in terms of concentrations and locations of plastic accumulation.

Intraspecific genetic lineages of a marine mussel show behavioural divergence when exposed to microplastic leachates

Worldwide, microplastic pollution has numerous negative implications for marine biota, exacerbating the effects of other forms of global anthropogenic disturbance. Mounting evidence shows that microplastics (MPs) not only cause physical damage through their ingestion, but also act as vectors for hazardous compounds by leaching absorbed and adsorbed chemicals. Research on the effects of plastic pollution has, however, largely assumed that species respond uniformly, while ignoring intraspecific diversity (i.e., variation within a single species). We investigated the effects of plastic leachates derived from factory-fresh (virgin) and beached microplastics on the behavioural responses of two genetic lineages of the Mediterranean mussel Mytilus galloprovincialis. Through laboratory behavioural experiments, we found that during exposure to leachates from beached microplastics (beached MPLs), Atlantic specimens moved significantly less than Mediterranean individuals in terms of both (i) proportion of individuals responding through movement and (ii) net and gross distances crawled. In contrast, no significant intraspecific differences were observed in the behaviour of either adults or recruits when exposed to MPLs from virgin microplastics (virgin MPLs). Additionally, the reception of cues from three amino acids (L-cysteine, proline and L-leucine) at increasing concentrations (10-5 M to 10-3 M in charcoal-filtered seawater) was tested by electrophysiological analysis using mussels exposed to beached MPLs or control seawater. We found significant intraspecific differences in response to 10-3 M L-cysteine (regardless of treatment) and 10-4 M L-cysteine (in mussels exposed to beached MPLs) and to 10-3 M proline (in mussels exposed to beached MPLs) and 10-5 M L-leucine. Our study suggests that intraspecific variation in a marine mussel may prompt different responses to plastic pollution, potentially triggered by local adaptation and physiological variability between lineages. Our work highlights the importance of assessing the effects of intraspecific variation, especially in environmental sentinel species as this level of diversity could modulate responses to plastic pollution.

Microplastics - A major contaminant in marine macro algal population: Review

Microplastics (MPs) are a significant concern in this modern environment, and the marine environment is a sink for them now. Researchers have taken an interest in marine microplastic studies recently, which has opened the door to research in macroalgae and microalgae. Macroalgae are the primary producers in maritime ecosystems and are economically significant. This review aimed to identify the microplastic interactions with marine macroalgae and the impacts of microplastics on macroalgae based on existing literature while also recognizing knowledge gaps. MPs were mostly fibers and polymers with notable production and application levels; their abundance differed among species. More MPs were found in filamentous species than in other types. The results of this study indicated that, in maritime environments, macroalgae contribute to MP biomagnification and bioaccumulation. Adequate studies are needed to fill the research gaps in this area of MPs in macroalgae and their effects.

The effect of interspecific and intraspecific diversity on microplastic ingestion in two co-occurring mussel species in South Africa

Interspecific and intraspecific diversity are essential components of biodiversity with far-reaching implications for ecosystem function and service provision. Importantly, genotypic and phenotypic variation within a species can affect responses to anthropogenic pressures more than interspecific diversity. We investigated the effects of interspecific and intraspecific diversity on microplastic ingestion by two coexisting mussel species in South Africa, Mytilus galloprovincialis and Perna perna, the latter occurring as two genetic lineages. We found significantly higher microplastic abundance in M. galloprovincialis (0.54 ± 0.56 MP items g-1WW) than P. perna (0.16 ± 0.21 MP items g-1WW), but no difference between P. perna lineages. Microbeads were the predominant microplastic (76 % in P. perna, 99 % in M. galloprovincialis) and polyethylene the prevalent polymer. Interspecific differences in microplastic abundance varied across locations, suggesting diverse sources of contamination. We suggest that microplastic ingestion can be species-specific even in organisms that coexist and play similar functional roles within ecosystems.