MEPS 546:123-133 (2016)  -  DOI: https://doi.org/10.3354/meps11622

ABSTRACT: Hypoxic zones in coastal ecosystems are rapidly expanding as global temperatures and anthropogenic inputs of nutrients continue to increase. These conditions can affect cellular homeostasis and pose serious threats to the fitness of a wide variety of organisms, including ecologically important bivalve species. The overall purpose of this study was to evaluate the effects of hypoxia on antioxidant status and tissue damage in two co-occurring bivalve species, eastern oysters Crassostrea virginica and Atlantic ribbed marsh mussels Geukensia demissa. We examined oysters and mussels collected from a reference site and exposed to different hypoxia regimes in the laboratory as well as bivalves collected from multiple field sites with varying hypoxia regimes. Glutathione (GSH) and lipid peroxidation levels were measured in hepatopancreas (HP) tissues as markers of overall antioxidant status and tissue damage, respectively. Increases in the concentrations of GSH, which is the most abundant cellular antioxidant and a reactive oxygen species scavenger, as well as elevated lipid peroxidation were observed in HP tissues of hypoxia-exposed bivalves. Species-specific differences in responses to hypoxia were also observed, and marsh mussels were found to be much more sensitive to hypoxia than oysters, as there were significant mortalities and higher lipid peroxidation levels in hypoxia-exposed mussels. The results and patterns from the field sites were found to be similar to those obtained from the laboratory studies. These studies suggest that hypoxia can cause increases in cellular damage, alter antioxidant status, and pose significant risks to estuarine bivalves. Assessments of species-specific differences using sublethal biomarkers are essential for developing habitat health criteria that are sufficiently protective for bivalves and other species.

KEY WORDS: Hypoxia · Biomarker · Bivalve mollusk · Oyster · Mussel · Estuary