Comparative predator-mediated habitat use in early juvenile southern Tanner crab (Chionoecetes bairdi), snow crab (Chionoecetes opilio), and red king crab (Paralithodes camtschaticus)

Abstract

Despite declining populations, southern Tanner crab (Chionoecetes bairdi), snow crab (Chionoecetes opilio) and red king crab (Paralithodes camtschaticus) support economically important fisheries in the Gulf of Alaska and the southeastern Bering Sea. In the southeastern Bering Sea these crab species have distinct although overlapping habitats. Juvenile snow crab, a stenothermic arctic species, are concentrated in waters below 2 °C, in contrast to the distributions of Tanner crab and red king crab which occupy much wider thermal ranges. Other aspects of the habitat associations of early benthic stages of Chionoecetes spp. have not been extensively studied. We describe habitat selection and predation avoidance strategies of early benthic stages (C1-C4) of Tanner crab, snow crab, and red king crab with experiments examining (1) sediment grain size associations, (2) burial behavior and (3) use of emergent benthic habitat structure (artificial worm tubes) in response to a predator presence, and (4) effect of worm tube density on the survival of age-0 Tanner crabs in the presence of predatory juvenile Pacific cod (Gadus macrocephalus) and age-1 Tanner crab. Tanner crabs were the only species that exhibited a clear sediment association, selecting silty muds to fine sand rather than larger sands and pebbles. Tanner and snow crabs buried deeper in sandy mud than in fine sand and both species significantly increased burial behavior in response to introduction of a cod predator. Conversely, red king crabs did not exhibit burial behavior even in the presence of a predator. Early juvenile Tanner and red king crabs displayed strong affinity for emergent structure, while snow crabs were evenly distributed between emergent structure and bare sand habitats. Contrary to expectations, crab selection of emergent structure was not significantly influenced by a cod predator presence. In trials with actively foraging predators, survival of juvenile Tanner crabs was higher in worm tube habitat. Our results demonstrate that early juvenile Tanner and snow crabs use burial behavior as the first line of avoidance/defense, while red king crabs rely upon occupancy of structurally complex habitat. Tanner crab affinity for worm tube structure may facilitate foraging in addition to serving as a refuge. Snow crabs settle on organically rich, fine sediments with little to no emergent structure in the eastern Bering Sea and may benefit from reduced predation pressure in cold waters, suggesting the importance of low temperature as a critical habitat feature for this species.