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.

Hard Clams (Mercenaria mercenaria) Evaluate Predation Risk Using Chemical Signals from Predators and Injured Conspecifics

“…Because blue crabs are generalist consumers and eat almost anything alive or dead (Virnstein, 1977;Eggleston et al, 1992;Micheli, 1995Micheli, , 1997, the threat of predation by crabs is unrelated to the crab's recent foraging activity. As in the previous example with slimy sculpins, knowledge of a blue crab's diet provides no valuable information for their prey, suggesting that it is not advantageous for clams to rely on diet cues as their sole means of evaluating risk.…”

Effects of predation by sea ducks on clam abundance in soft-bottom intertidal habitats

“…Numerous studies of marine communities have demonstrated effects of predators on the abundance, size distribution, and other attributes of their prey, with subsequent consequences for community structure and function (Paine 1966, 1974, Virnstein 1977, Kvitek et al 1992, Langlois et al 2005. In rocky intertidal habitats, which are often characterized by intense competition for space, predators may have a marked, indirect effect on the abundance of certain species by directly limiting the abundance of their strongest competitors (Paine 1966(Paine , 1974.…”

“…In rocky intertidal habitats, which are often characterized by intense competition for space, predators may have a marked, indirect effect on the abundance of certain species by directly limiting the abundance of their strongest competitors (Paine 1966(Paine , 1974. In soft-bottom marine habitats, however, infaunal animals are not generally limited by interspecific competition for space, and the abundance of infaunal animals is often directly affected by their major predators (Virnstein 1977, Peterson 1979, Wilson 1989, Estes & Peterson 2000.…”

“…Previous studies have identified invertebrate predators, such as crabs and polychaetes, as having considerable predation effects in soft-bottom intertidal areas (Virnstein 1977, Commito 1982, Hines et al 1990, Eggleston et al 1992. These invertebrate predators are often numerically abundant and widespread throughout their available habitat and can thus exert strong predation pressure on infaunal animals.…”

“…These invertebrate predators are often numerically abundant and widespread throughout their available habitat and can thus exert strong predation pressure on infaunal animals. Vertebrate predators can also have significant predation effects in soft-bottom habitats, although they are typi-cally far less abundant than invertebrate predators (Virnstein 1977, Quammen 1984, Wilson 1989, Kvitek et al 1992. Vertebrate predators tend to have higher feeding rates and increased mobility, allowing them to quickly respond to variation in prey abundance.…”