Abstract: | The intentional introduction of a species for the enhancement of stock or establishment of new fisheries, often has unforeseen
effects. The red king crabs, Paralithodes camtschaticus, which was introduced into the Barents Sea by Russian scientists, has established a self-sustaining population that has expanded
into Norwegian waters. As top benthic predators, the introduced red king crabs may have possible effects upon native epifaunal
scallop (Chlamys islandica) communities. These benthic communities may be a source of prey species in late spring, when the red king crabs feed most
intensively. Foraging rates (consumption, killing or severely damaging) of red king crab on native prey organisms were measured
by factorial manipulation of crab density (0.5, 1.5 and 3 per m 2), size classes (immature, small mature, and large mature crabs), and by evaluating prey consumption after 48 h, in order
to extrapolate a scenario of the likely impacts. Foraging rates of the red king crab on scallops ranged between 150 and 335
g per m2 within 48 h. These rates did not change when crab density was altered, though an increased amount of crushed scallops left
uneaten at the tank floor, were correlated with high density of small mature crabs. Foraging rate changed significantly with
crab size. Consequently, the susceptibility of native, shallow water epibenthic communities to red king crab predation in
the early life history stages, and during the post-mating/molting spring period, must be considered significant when foraging
rates are contrasted with natural scallop biomass between 400 and 1200 g scallops per m2. |