Eastern Bering Sea

SEA ONION

Taxonomy: Phylum Urochordata, class Ascidiacea, order Stolidobranchia, family Pyuridae, species Boltenia ovifera

Distribution and Life History: Boltenia ovifera, a stalked, solitary ascidian, is widely distributed in the North Atlantic and North Pacific. See the sea potato (Styela rustica) account for generic information on ascidian life history.

Boltenia ovifera - Locally abundant north of the Alaska Peninsula (Kessler, 1985). Found in the Okhotsk and Bering Seas, mainly at depths of 25-100 m, usually together with sponges and hydroids (Ushakov, 1955b). Sexual reproduction results in the formation of a tadpole larva that is free-swimming for only hours before it settles on a hard substrate and begins it’s metamorphosis to the adult form. In the Bay of Fundy, the tadpole larvae appeared in the plankton in January and February, far preceding the appearance of any other plankton (Lacalli, 1981). The adult sea onion has a white or pinkish bulb-like body that floats in the water column and is tethered to the bottom by a stalk that terminates in a root-like holdfast or hapteron. The stalk is usually two to three times the length of the bulbous body, with the entire animal reaching 30 cm or more in length (Kessler, 1985). Compound ascidians like Molgula sp, bryozoans and hydroids are frequently attached to its stems and holdfasts. Sea onions and associated attached invertebrates are know to provide habitat to small juvenile red king crab (Paralithodes camtschaticus) (McMurray et al., 1984, Stevens and Kittaka, 1998).