Effects of Tropical Storm Agnes on soft-bottom macrobenthic communities of the James and York estuaries and the lower Chesapeake Bay

Macrobenthos was studied at 58 previously surveyed stations following the drastic salinity reductions caused by Tropical Storm Agnes. Effects were greatest in the lower, polyhaline portions of the James and York estuaries, where many abundant species were eliminated from shallow bottoms due to the usually low salinities and several species were eliminated or reduced in abundance on deeper bottoms due to the somewhat reduced salinity but, more importantly, to low oxygen concentrations resulting to strong density stratification of the water masses. Irruptions of opportunistic species followed these perturbations and the deep mud bottom community in the lower York estuary had not recovered 2 1/2 years after the storm. The primary alteration to usually mesohaline communities was an infusion of species more abundant in oligohaline and/or shallow brackish habitats. Communities in usually, oligohaline or tidal freshwater reaches of the James and York estuaries and those at the mouth of the bay were hardly affected by Agnes.