Foraging behavior of an estuarine predator, the blue crab Callinectes sapidus in a patchy environment

Abstract

. 2000. Foraging behavior of an estuarine predator, the blue crab Callinectes sapidus in a patchy environment. -Ecography 23: 21 -31.To define general principles of predator-prey dynamics in an estuarine subtidal environment, we manipulated predator density (the blue crab, Callinectes sapidus) and prey (the clam, Macoma balthica) patch distribution in large field enclosures in the Rhode River subestuary of the central Chesapeake Bay. The primary objectives were to determine whether predators forage in a way that maximizes prey consumption and to assess how their foraging success is affected by density of conspecifics. We developed a novel ultrasonic telemetry system to observe behavior of individual predators with unprecedented detail. Behavior of predators was more indicative of optimal than of opportunistic foraging. Predators appeared responsive to the overall quality of prey in their habitat. Rather than remaining on a prey patch until depletion, predators appeared to vary their patch use with quality of the surrounding environment. When multiple (two) prey patches were available, residence time of predators on a prey patch was shorter than when only a single prey patch was available. Predators seemed to move among the prey patches fairly regularly, dividing their foraging time between the patches and consuming prey from each of them at a similar rate. That predators more than doubled their consumption of prey when we doubled the number of prey (by adding the second patch) is consistent with optimizing behaviors -rather than with an opportunistic increase in prey consumption brought about simply by the addition of more prey. Predators at high density, however, appeared to interfere with each other's foraging success, reflected by their lower rates of prey consumption. Blue crabs appear to forage more successfully (and their prey to experience higher mortality) in prey patches located within 15 -20 meters of neighboring patch, than in isolated patches. Our results are likely to apply, at least qualitatively, to other crustacean-bivalve interactions, including those of commercial interest; their quantitative applicability will depend on the mobility of other predators and the scale of patchiness they perceive.

Behavioral responses of free-ranging blue crabs to episodic hypoxia. II. Feeding

“…data). This is inconsistent with previous laboratory (Lipcius & Hines 1986, Mansour & Lipcius 1991, Eggleston et al 1992) and field studies (Clark et al 2000. Collectively, these results suggest that blue crabs may rely on alternative sources of prey in the NRE especially during late summer months when infaunal prey availability is limited.…”

Density-dependent predation by blue crabs Callinectes sapidus on natural prey populations of infaunal bivalves

“…We did not include the 10 clams m -2 treatment level used in the field experiment in order to reduce the number of treatment combinations and to reduce the likelihood of all the clams being consumed in the 2 crab treatments. Experimental crab densities are higher than those found naturally over large areas but are similar to those at prey patches where crabs aggregate (Clark et al 1999b(Clark et al , 2000. Experimental clam densities fall within the lower end of natural clam densities in the Rhode River (Eggleston et al 1992, Seitz et al 2001 (Table 1).…”

“…These results suggest that, at low prey density, crabs facilitate rather than interfere with each other's foraging. Facilitation could occur if the chemical cues of crabs macerating clams stimulate other crabs to forage in the same area (Clark et al 2000).…”

How small-scale variation in oyster reef patchiness influences predation on bivalves

“…None of the sessile prey types used in our experiments exhibited a pattern of higher predation mortality inside patchier habitat, implying that guild type may be important to how predation risk in bivalves changes with habitat patch size. Supporting field evidence also shows that mobile bivalves experience higher predation in patchy environments (Bologna & Heck 1999, Clark et al 2000. Although there is little guidance in the literature to infer possible mechanisms behind changes in sheepshead foraging behavior with habitat patchiness, their strong disturbance of continuous oyster habitat during foraging might have led to higher predation rates on small oysters in continuous than in fine-scale patchy habitat, which they disturbed less.…”