Classification: Unlisted Invasive Species
aquatic managers ask the public to report sightings of tunicates
and other aquatic invasive species. To report sightings contact:
Aquatic nuisance species coordinator for WDFW
WDFW Assistant aquatic nuisance species coordinator
A colonial tunicate (“sea squirt”) introduced from Europe, Botryllus schlosseri is a colonial tunicate consisting of many small individuals called zooids. Each zooid pumps water through its own siphon, filters out oxygen and feeds on small organisms such as phytoplankton, zooplankton, oyster and mussel larvae, and other suspended organic materials. It then discharges the filtered water and waste into a common center of a system of other zooids, typically arranged in a star-shaped cluster, where it exits out a small pore. A colony consists of many of these star-shaped clusters linked together within a purple to brown or clear, firm, fleshy matrix. A single cluster is usually less than one-half inch in diameter and may have up to about 20 zooids. Each zooid within a colony is of the same color. The color of separate colonies, however, can vary between orange, yellow, black, gray-green, or white.
B. schlosseri prefers protected marine waters and can reproduces rapidly, fouling ship hulls, docks, piers and shellfish aquacultures. It can attach to a variety of solid surfaces including gravel, seabed, metal, tires, plastic, styrofoam, rope, fiberglass, wood, and shellfish.
Unlike the solitary tunicates, the colonial B. violaceus broods its larvae internally by the fertilization of its eggs from male gametes of nearby colonies. It then releases the planktonic larvae into the water column where it eventually settles on a firm surface where it metamorphoses into a zooid and then buds off to the sides asexually to form the multiple star-shaped systems that make up a colony. The larvae are very short lived, likely settling onto a firm surface and near the point of origin. However, fragments from a colony can survive indefinitely, reproducing asexually while drifting, or traveling within ship ballast water to colonize new areas.
See the Tunicate information page for more information.