Eastern Bering Sea

HYDROIDS

Taxonomy: Phylum Cnidaria, class Hydrozoa, orders Hydroida and Stylasterina

Species Representatives: Sertularia robusta, Hydractinia sp.

Distribution and Life History: Hydroids are small, mostly colonial animals in the cnidarian Class Hydrozoa. About 200 species have been identified in Alaska (O'Clair and O'Clair, 1998). The species encountered on the NMFS trawl survey have yet to be identified. Most of these are colonial forms that are either erect and tree-like, or prostrate encrustations on mollusk shell (live or dead), rock, and other hard surfaces. The erect species generally grow no taller than 15 cm. Some hydroids have alternating benthic and pelagic generations. The pelagic medusae are like tiny jellyfish. Reproduction in the group is varied and complex, with many species having a free-swimming planula larva that spends hours to days in the water column before settling to the bottom (Barnes, 1980).

On the west Kamchatka Shelf, a rich assemblage dominated by hydroids, bryozoans, and sponges was the favored habitat of young-of-the-year red king crab (Paralithodes camtschaticus) and hydroids were considered to be their main food. On stations where young crab were caught, hydroids averaged more than 50% of the total biomass (Tsalkina, 1969). Such strong linkage is not suspected in the SE Bering Sea , although hydroids are part of the sessile invertebrate communities where young-of-the-year red king crab occur (McMurray et al., 1984, Stevens and MacIntosh, 1991). In the SE Bering Sea, the hermit crab Labidochirus splendescens (splendid hermit) is typically found in a moon snail shell encrusted with the velvet textured hydroid Hydractinia sp. (Kessler, 1985).