Effects of Tropical Storm Agnes on Epifaunal Invertebrates in Virginia Estuaries

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Abstract
The low-salinity regimes in Chesapeake Bay that followed the passage of Tropical Storm Agnes produced unprecedented changes in distributions and abundances of estuarine biota. After the initial surge of fresh water from the Virginia river basins, a second larger flow from the Susquehanna River basin cut off supplies of salt water from the Chesapeake Bay and ocean sumps. This later surge prolonged epifaunal exposure to low salinities of 10 o/oo to 9 days at the mouth of the James River and about 50 days in the Rapahannock River. The lower sectors of the Virginia rivers, where mesohaline species normally live, were most affected. Oligohaline species such as oysters, barnacles, and hooked mussels were severely stressed and many individuals died, but eradication did not occur. Mesohaline species including all sponges, tunicates, echinoderms, many mollusks, and many predators and scavengers, oyster drills, spider crabs, ect., were eliminated from large areas including whole rivers. Recovery of some species, e.g. sea squirts and red sponge, is progressing rapidly but others, colonial tunicates, yellow sponges, oyster drills, ect., may require years. The slowest will be those without pelagic larvae, and those where breeding populations were greatly reduced or eliminated. Oyster drills are an important example. Certain hydroid and bryozoan species with oligohaline affinities extended their distributions and abundances dramatically. The most prominent eruptive species were in the generaAcanthodesia, Garveia, andAnguinella. This report begins with a description of established communities and follows changes of faunal groups due to freshwater and low-salinity exposure. By contrast, most fouling studies of the past began with clean surfaces. After the initial mortalities, open niches were quickly colonized by opportunistic species, thereby initiating new estuarine successions for continuing observations.

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