Noncommercial benthic fauna

Eastern Bering Sea


The sea potato, Styela rustica.

Phylum Urochordata, class Ascidiacea, order Stolidobranchia, family Styelidae, species Styela rustica

Distribution and Life History: Styela rustica is one of several common ascidians (tunicates, sea squirts) in the SE Bering Sea. Ascidians are sessile (permanently attached) animals that are either solitary or colonial (Ushakov, 1955b). Solitary ascidians are rather large, with a sack-like body attached to the substrate either by a flattened base, which may have a root-like hapteron, by a stalk, or by the ventral surface (Ushakov, 1955b). The free end of the body is equipped with two siphons through which water enters and exits the body. Ascidians can reproduce both sexually and asexually. Sexual reproduction results in the formation of a tadpole larva that is free-swimming for only minutes or hours before it settles on a hard substrate (O'Clair and O'Clair, 1998). The few predators that are known to take ascidians include some flatworms, gastropod mollusks, crabs, sea stars, and some fishes (O'Clair and O'Clair, 1998). Ascidians are suspension feeders, with prey including a variety of invertebrate larvae (Bingham and Walters, 1989).

Styela rustica - Abundant north of the Alaska Peninsula (Kessler, 1985). Jewett and Feder (1981) found it to make up over five percent of the benthic invertebrate biomass in the SE Bering Sea, and smaller percentages in the NE Bering Sea and SE Chukchi Sea. It was most common in the 40 to 100 m depth range. Styela has a dark brown, potato-shaped body that reaches a maximum height of about 10 cm (Kessler, 1985). It usually grows in clumps that are attached to the substrate, dead snail or clam shell, or sessile invertebrates such as mussels and other ascidians.