, Volume 10, Issue 3, pp 227-245

Long-term variation in mesohaline Chesapeake Bay macrobenthos: Spatial and temporal patterns

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Abstract

Macrobenthos, sediments, and environmental conditions were sampled in the mesohaline region of western Chesapeake Bay (1971–1984) and the Potomac River (1980–1984). The survey data were used to quantify variation in macrobenthos and the physicochemical environment due to seasonal dynamics, spatial pattern (regional and local), and annual as well as long-term trends. Field experiments were conducted to test hypotheses suggested by the analysis of the survey data. Long-term and regional changes in the physiochemical environment, particularly salinity and dissolved oxygen concentration, had major influences on regional and long-term abundance patterns of macrobenthos. Two major species groups were identified along the mesohaline salinity gradient: those characteristic of high and low mesohaline salinities. Salinity increased and dissolved oxygen concentration below the pycnocline declined over the 14 yr. Estuarine endemic and euryhaline marine species concomitantly decreased in abundance. Opportunist species responded to increasing salinity and declining oxygen levels with increases in abundance. Predation on macrobenthos by fish and crabs affected the amplitude of annual recruitment pulses. Food availability apparently determined the magnitude of summer macrobenthic mortality. Spring was a critical period for the establishment of distributional patterns. The macrobenthos of the upper Chesapeake Bay was relatively stable over the study period mainly due to the stability and predictability of physicochemical processes controlling recruitment patterns.