The Importance of Predation by Crabs and Fishes on Benthic Infauna in Chesapeake Bay

Abstract

The significance of large motile predators in controlling the distribution and abundance of the macrobenthic invertebrates within the sediments (the infauna) in a shallow subtidal sand community was tested using manipulative field experiments. The blue crab (Callinectes sapidus) and 2 species of bottom—feeding fishes, spot (Leiostomus xanthurus) and hogchoker (Trinectes maculatus), were either excluded from or confined to small areas using wire mesh cages. Callinectes and Leiostomus effectively reduced infaunal desnities; Trinectes did not. The infauna responded to decreased predation with a large increase in density and diversity within 2 mo. The large population increases were exhibited by opportunistic species, which are considered to be most subject to predaton. Species whos populations where least affected by predation were those species which live deep in or quickly retract into the sediment. These species thus avoid predation and were generally the dominat species in the natural community. For species whose density increased greatly in exclosures, recruitment was by planktonic larvae and growth was very rapid, individuals grwoing to maturity in only a few months. Densities of all infaunal species increased in exclosures, suggesting that their population densities under natural conditions are not controlled by competitive interactions. In community, infaunal population sizes are limited by predation and not by food or space. Severe predation pressure and physical disturbances, particulary sediment instability, keep population levels far below the carrying capacity of the environment. Severe predation, and the rapid growth, short generation times, and rapid turnover rates of constituent populations suggest that such infaunal communities, despite a low standing crop, are an important food source for predator species important to man.