Lethal and sublethal effects of simulated dredged sediment deposition on overwintering blue crabs Callinectes sapidus

Abstract

Regular maintenance of waterways and ports requires dredging and disposal of accumulated sediment, which can injure or kill infaunal and epifaunal species. Our understanding of the lethal and sublethal effects of dredged sediment deposition in marine communities is based predominantly on benthic infaunal species, whereas knowledge of the effects of these additions on mobile macrofauna is limited. We explored lethal and sublethal effects of simulated dredged sediment (hereafter, sediment) on blue crabs Callinectes sapidus. Twenty mature female crabs were allocated into 4 treatments: no sand, no sediment; sand, no sediment; sand + 2.5 cm sediment; and sand + 10.0 cm sediment. Accounting for size, mortality in the 10 cm sediment treatment was immediate and 10- to 20-fold higher than that in other treatments. Crabs that eventually died also experienced sublethal effects as evidenced by a reduced behavioral repertoire. These results suggest that in winter, all mature female crabs will suffer high mortality under 10 cm of dredged sediment deposition, while smaller crabs may suffer substantial mortality and sublethal effects at even lower levels. As blue crab activity is temperature dependent, the detrimental effects can be minimized by disposing of dredged sediment either where crabs are not abundant or when water temperatures are higher and blue crabs can avoid burial.