Effects of the zebra mussel on nitrogen dynamics and the microbial community at the sediment-water interface

Abstract

A flow-through expenment was conducted on intact cores of sedunents from Saginaw Bay, Lake Huron, to examine how trophic interactions between filter-feeding bivalve mussels and microbial populations could affect nitrogen dynamics at the sediment-water interface. The zebra mussels used in this experiment removed a large proportion of protozoa and phytoplankton from the overlying water, particularly heterotrophic nanoplankton (up to 82 %), while bacterial population~ showed less change. A 3-fold decrease in the protozoan to bacterial carbon ratio corresponded to a 2.5-fold increase in relative ammonium removal rates as estimated from the dark loss of '5N-ammonium. Excretion by the bivalves also increased net ammonium flux to the water, thus elevating the total calculated area1 ammonium removal rates to about 6-fold over rates observed in the control treatment. These data suggest that filter-feedng bivalves may significantly affect nitrogen transformation rates near the sediment-water interface by excreting ammonium and altering the microbial food web structure at the sediment-water interface.