Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

1990

Journal

Bulletin of Marine Science

Volume

46

Issue

1

First Page

62

Last Page

82

Abstract

Blue crabs (Callinectes sapidus) are major predators of juvenile oysters (Crassostrea virginica) in Chesapeake Bay, yet little information exists on the foraging behavior and predatorprey dynamics for this predator-prey system. Laboratory experiments assessed functional responses of blue crabs to six densities of three size-classes of juvenile American oysters. Behavioral subcomponents of the crabs' functional response were quantified: total and successful encounter rates, proportional attack success, persistence time in unsuccessful encounters, and breaking, eating and handling times in successful encounters. Specific opening techniques were used by crabs for the three oyster size-classes. Blue crabs exhibited a hyperbolic type II functional response regardless of oyster size, with an inverse relationship between predation rates and increasing oyster size. Crab persistence times with oysters were positively correlated with attack success rates at three oyster size-classes, and inversely related to prey density, suggesting higher selectivity by blue crabs at higher oyster densities. Oysters >30 mm shell-height may be near the critical size for crushing by large crabs as a result of increased variations in (I) shell to crab strength ratios, (2) opening techniques with oyster attachment site and growth geometry, and (3) oyster density. These findings indicate that crab acceptance or rejection sequences of bivalve prey depend on prey density and size, that predation by large male C. sapidus can lead to local extinction of juvenile oysters (x = 15- 35 mm SH) regardless of density and, that increasing shell-height provides a refuge from predation.

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