Baseline assessment of microplastics in commercially important marine bivalves from New York, U.S.A

Microplastic (MP) contamination in bivalve mollusks has become a significant concern over the last few years. These ecologically and economically valuable species are popular seafood items for human consumption. As filter feeders, bivalves may ingest MPs in their bodies, possibly impacting their physiology and fitness. Additionally, a considerable amount of the seafood that humans consume comes from coastal areas where MP concentrations tend to be the highest. This research provides the first examination of MPs in eastern oysters (Crassostrea virginica) and hard clams (Mercenaria mercenaria) that were grown locally in coastal areas of New York, contributing to a baseline for the northeast and mid-Atlantic regions of the U.S. A total of 48 eastern oysters (n = 12 per site, at four sites) and hard clams (n = 24 per site, at two sites) were sampled in summer 2021. While MP fibers and fragments (i.e. polyethylene terephthalate, polystyrene, and polypropylene) were found in some oysters, other contaminants (e.g. indigo dye, phthalocyanine, dye 823, etc.) were found in both bivalve species. Particle composition was verified using Raman microspectroscopy. Although mean MP concentrations were low in eastern oysters (i.e. 0.008 MPs g^-1 of soft tissue wet weight; 0.125 MPs ind^-1) and not found in hard clams, more research is needed to assess the magnitude of contamination in these edible bivalves.

Harmful dinoflagellate Cochlodinium polykrikoides impairs the feeding behavior of larval sheepshead minnows (Cyprinodon variegatus)

Research evaluating the toxicity of the harmful dinoflagellate Cochlodinium (a.k.a. Margalefidinium) polykrikoides has been dominated by acute bioassays while the sublethal effects remain less well understood. This study examined the sublethal effects of C. polykrikoides exposure on the feeding behavior of larval estuarine fish. Sheepshead minnow (Cyprinodon variegatus) larvae were used in feeding experiments which assessed the total consumption of zooplankton prey (i.e., Artemia nauplii) over defined time periods. Larvae exposed to intermediate concentrations (i.e., 10²  cells ml^-1 ) of clonal cultures of C. polykrikoides saw statistically significant reductions (range = 10%-81%) in the Artemia consumed compared to controls (i.e., filtered seawater, culture media or nontoxin producing dinoflagellate). These reductions were found independent of whether the larvae were fed or starved prior to experimentation. As these concentrations are similar to those typically found during mild blooms or at the periphery of dense blooms, these findings have significant implications for the feeding behavior of ichthyoplankton.

Effects of methylmercury on the early life stages of an estuarine forage fish using two different dietary sources

Marine fish accumulate methylmercury (MeHg) to elevated concentrations, often higher than in freshwater systems. As a neurotoxic compound, high MeHg tissue concentrations could affect fish behavior which in turn could affect their populations. We examined the sublethal effects of MeHg on larvae of the Sheepshead minnow (Cyprinodon variegatus), an estuarine fish, using artificial or natural diets with varying MeHg concentrations (0-4.8 ppm). Larvae were fed control and MeHg-contaminated diets at low or normal (10% of their body mass) daily food rations from 7 to 29 days when they reached juvenile stage. Growth, respiration, swimming activity and prey capture ability were assessed. Food ration affected Hg toxicity in our study. Natural diets containing 3.2 ppm MeHg had no impacts on growth and swimming in fish that were fed normal food rations but depressed growth and swimming at low food rations. MeHg toxicity did not differ between artificial and natural foods, however fish accumulated more MeHg from the former. Artificial food containing 4.8 ppm MeHg only affected prey capture after 21 days of exposure. Sheepshead minnows, a forage fish species occupying a low trophic level in coastal waters, can be MeHg tolerant, especially when food is abundant, and can serve as an enriched Hg source for higher trophic level predators.

Effects of the harmful algae, Alexandrium catenella and Dinophysis acuminata, on the survival, growth, and swimming activity of early life stages of forage fish

The effects of co-occurring harmful algal blooms (HABs) on marine organisms is largely unknown. We assessed the individual and combined impacts of the toxin producing HABs, Alexandrium catenella and Dinophysis acuminata, and a non-toxin-producing HAB (Gymnodinium instriatum) on early life stages of two estuarine fish species (Menidia beryllina and Cyprinodon variegatus). Lethal (i.e. time to death) and sublethal (i.e. growth, grazing rate, and swimming activity) effects of cultured HABs were investigated for eleutheroembryo and larval life stages. Mixed algal treatments (i.e. A. catenella and D. acuminata mixtures) were often equally toxic as A. catenella monoculture treatments alone, although responses depended on the fish species and life stage. Fish exposed to toxin producing HABs died significantly sooner (i.e. <1-3 days) than controls. Significant differences in sublethal effects were also found between fed controls and toxic HAB treatments, although responses were often similar to G. instriatum or starved controls. Collectively, the results demonstrate that HABs may reduce fish productivity and fitness.