Phytoplankton uptake by a resilient urban estuary bivalve, Mytilopsis leucophaeata

Abstract

Urban estuaries face numerous problems stemming from excess nutrients from stormwater runoff. Baltimore Harbor, an urban estuary, has intense and frequent phytoplankton blooms that can lead to hypoxic and anoxic zones, and ultimately fish kills. Efforts to reduce the nutrients, that fuel algae blooms, focus on point sources and not remediation once the nutrients have entered the water. In water removal of nutrients is often in the form of phytoplankton uptake by bivalve suspension feeders. Commercial bivalve species have been studied for their ability to remove phytoplankton and sequester nutrients in the coastal zone. In urban estuaries, commercially important bivalves often do not naturally occur, or urban pollution would make them unsuitable for human consumption. Therefore, we set out to determine if a locally abundant non-commercial mussel, Mytilopsis leucophaeata, could reduce phytoplankton levels and how environmentally relevant temperature and salinity may impact clearance rates. Our study developed a standard method to quantify phytoplankton removal of two cultured phytoplankton species (Isochrysis sp. and Chaetoceros sp.), by measuring both in vivo and extracted chlorophyll. We then evaluated the ability of the mussels to remove algae under varied temperatures and salinity that are typical for Baltimore Harbor. Our results show that at lower temperatures there is a lower clearance rate, and salinity did not significantly affect the clearance rates of the mussels. Overall, our results show potential for the use of this native non-commercial bivalve to reduce phytoplankton blooms in Baltimore Harbor.