Bioreactivity and Microbiome of Biodeposits from Filter-Feeding Bivalves

Bivalves serve an important ecosystem function in delivering organic matter from pelagic to benthic zones and are important in mediating eutrophication. However, the fate of this organic matter (i.e., biodeposits) is an important consideration when assessing the ecological roles of these organisms in coastal ecosystems. In addition to environmental conditions, the processing of biodeposits is dependent on its composition and the metabolic capacity of the associated microbial community. The objectives of this study were to compare the biological reactivity, potential denitrification rates, and microbial communities of biodeposits sourced from different bivalve species: hard clam (Mercenaria mercenaria), eastern oyster (Crassostrea virginica), and ribbed mussel (Geukensia demissa). To our knowledge, this is the first study to investigate and compare the microbiome of bivalve biodeposits using high-throughput sequencing and provide important insight into the mechanisms by which bivalves may alter sediment microbial communities and benthic biogeochemical cycles. We show that clam biodeposits had significantly higher bioreactivity compared to mussel and oyster biodeposits, as reflected in higher dissolved inorganic carbon and ammonium production rates in controlled incubations. Potential denitrification rates were also significantly higher for clam biodeposits compared to oyster and mussel biodeposits. The microbial communities associated with the biodeposits were significantly different across bivalve species, with significantly greater abundances of Alteromonadales, Chitinophagales, Rhodobacterales, and Thiotrichales associated with the clam biodeposits. These bioreactivity and microbial differences across bivalve species are likely due to differences in bivalve physiology and feeding behavior and should be considered when evaluating the effects of bivalves on water quality and ecosystem function.