Red king crab ( Paralithodes camtschaticus) early post-settlement habitat choice: Structure, food, and ontogeny

Abstract

Little is known about nursery habitat function for red king crab ( Paralithodes camtschaticus), a commercially important species that associates with complex benthic habitats from settlement through the first two years of life. During settlement, the red king crab actively seeks complex benthic habitats, with high availability of vertical structure and crevice space. Habitat choice for early juvenile red king crab may be driven by habitat complexity, or a function of several potential mechanisms, including foraging requirements, and shifting ontogeny. We established habitat preference and foraging behavior for two size classes of age-0 red king crab (small 2–4 mm, and large 7.5–9 mm carapace length) with laboratory experiments using habitat treatments composed of individual complex substrates that were living, biogenic substrates, including structural invertebrates, bryozoans and hydroids, and macroalgae in branched and blade forms. Non-living structural mimics of the biogenic substrates were presented to crabs as clean and fouled mimic treatments. We quantified the proportion of crab associations and foraging activity with single habitat treatments within a 24 h period. Substrates that were statistically attractive to small crabs were paired to test small crab foraging behavior. A variety of substrates were statistically attractive to red king crab. Small crabs associated with complex biogenic habitats and fouled mimics (group mean ± SE 64% ± 4%) more often than clean mimics (29% ± 4%), and preferred to forage on the structural invertebrates (foraging frequency 81%) when presented with paired biogenic and fouled mimic substrates. Large crabs associated with habitats composed of structural invertebrates (group mean ± SE 78% ± 2%) statistically more often than macroalgae and fouled and clean mimics (32% ± 5%). Strong attraction to structural invertebrates by early juvenile red king crab is likely driven by foraging opportunities. Our experiments demonstrate that biological habitat features may be functionally more important to early juvenile red king crab than complex physical structure alone. Habitats formed by structural invertebrates, in particular, may enhance growth and survival of early post-settlement stage red king crab in excess of other highly structured habitats, including macroalgae and complex physical substrates.