Quantifying Eelgrass Habitat Loss in Relation to Housing Development and Nitrogen Loading in Waquoit Bay, Massachusetts

Abstract

Change analysis of eelgrass distribution in Waquoit Bay demonstrated a rapid decline of eelgrass habitat between 1987 and 1992. Aerial photography and ground-truth assessments of eelgrass distribution in the Waquoit Bay National Estuarine Research Reserve documented progressive loss in eelgrass acreage and fragmentation of eelgrass beds that we relate to the degree of housing development and associated nitrogen loading, largely via groundwater, within various sub-basins of the estuary. The sub-basins with greater housing density and higher nitrogen loading rates showed more rapid rates of eelgrass decline. In eelgrass mesocosm studies at the Jackson Estuarine Laboratory, excessive nitro- gen loading stimulated proliferation of algal competitors (epiphytes, macroalgae, and phytoplankton) that shade and thereby stress eelgrass. We saw domination by each of these three algal competitors in our field observations of eelgrass decline in Waquoit Bay. Our study is the first to relate housing development and nitrogen loading rates to eelgrass habitat loss. These results for the Waquoit Bay watershed provide supporting evidence for management to limit development that results in groundwater nitrogen loading and to initiate remedial action in order to reverse trends in eelgrass habitat loss.