Abstract
Blue king crabs (Paralithodes platypus) are commercially and ecologically important in Alaska, USA, but population abundances have fluctuated over the past several decades likely resulting from a combination of environmental and biological factors, including recruitment variability. Cannibalism between cohorts may be a source of mortality limiting recruitment success in the wild, but the degree of inter-cohort cannibalism is unknown for early benthic phase blue king crabs. In laboratory experiments, we evaluated the effects of habitat type (sand and shell) on the predator functional response and foraging behavior of year-1 blue king crabs as predators of year-0 conspecifics and examined the effects of predator presence on crypsis of prey crabs. In sand, consumption rates increased with predator size and prey density until satiation, while predation rates in shell were low regardless of predator size or prey density. These differential predation rates yielded a type III functional response in sand but a type I functional response in shell habitat. Crypsis of prey crabs was generally high and did not change in the presence of predators. Predator foraging activity was reduced in shell and may be an adaptive behavior to balance foraging efficiency and susceptibility to larger predators. Our results demonstrate that early benthic phase blue king crabs are cannibalistic between cohorts in the laboratory and that shell material is extremely effective for reducing encounter rates with conspecific predators. The distribution and abundance of such habitat may be important for recruitment success in some populations. Future studies should compare benthic habitat and species assemblages in areas with variable abundances, such as the Pribilof Islands and Saint Matthew Island in the eastern Bering Sea, to better understand possible mechanisms for recruitment variability.
Highlights
Cannibalism is widespread in the animal kingdom and occurs among both vertebrates and invertebrates [1,2]
The functional response can determine the stability of predator-prey relationships and whether prey persistence is possible; type II functional responses can be destabilizing to predator-prey relationships because proportional predation rates are highest at low prey densities, whereas type III functional responses are stabilizing as predation rates are lowest at low prey densities[16]
The data were unable to differentiate among the functional response models (Table 1), likely because of low predation rates at all prey densities (Fig. 1B)
Summary
Cannibalism is widespread in the animal kingdom and occurs among both vertebrates and invertebrates [1,2]. Stomach content analysis and field surveys have documented cannibalism in various decapod crustacean species in the wild [3,4,5,6,7,8,9] showing that it is a natural behavior. Cannibalism may be intense during periods of strong recruitment and may influence population dynamics of some crustacean species [6,7,10,11,12]. Three common types of functional responses include type I or density-independent, type II or inversely density-dependent, and type III or densitydependent. The functional response can be changed by a number of factors including habitat (e.g., [17,18,19]), the presence of alternative prey [20,21], predator size [22], prey size [23], and the spatial arrangement of prey patches [24,25]
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