Predatory Capacity of King Crabs in Antarctica
For millions of years, cold water temperatures have excluded shell-crushing (durophagous) predators from continental-shelf environments off the western Antarctic Peninsula. Recently, however, king crabs, Paralomis birsteini, have been found in dense, reproductively viable populations on the upper continental slope, and rapid warming might enable them to expand to the shelf. King crabs are crushing shelled invertebrates on the slope, but calcification of sturdy, shell-crushing chelae is likely inhibited by the low saturation state of high-Mg calcite in the deep Southern Ocean. The objectives of this study were to better understand the predatory capacity of P. birsteini by estimating the potential force generation of their chelae and the allocation of calcium carbonate in their exoskeletons. The potential force generation of the crab chelae was compared with the force required to crush their prey. The allocation of calcium-carbonate was compared with temperate, shallow-water species of brachyuran crab to infer the selection pressures on polar, deep-sea crabs. P. birsteini can generate about eight times more force than what is required to crush their shelled, invertebrate prey. They allocate more calcium-carbonate resources to their chelae than to their carapaces, in contrast to brachyurans living in temperate, shallow-water environments. This difference in resource allocation is likely a consequence of the limited predation pressure on the king crabs and the energetic cost of calcification in cold water.