Tunicate - Invasive Species

Invasive Species

Over the past few years, urochordates (notably of the genera Didemnum and Styela) have been invading coastal waters in many countries, and are spreading quickly. The carpet tunicate (Didemnum vexillum) is a mat-like organism that can smother other sea life, has very few natural predators, and is causing much concern. D. vexillum colonies are yellowish cream in color, and look like thick sponge-like masses and can overgrow objects on the sea floor such as gravel, mollusc shells, and possibly other encrusting species. These colonies are flexible, irregular, long, flat, and often exist as branched outgrowths projected from the surface referred to as tendrils. Some of the tendrils result from the colony encrusting worm tubes or other cylindrical objects but many are solid with a firm gelatinous core. The individuals of the colony are called zooids and many zooids with individual siphonal openings cover the surface of the colony.

Introduction of invasive tunicates usually occurs by transport on the hulls of ships and possibly in ballast water. Current research indicates that many tunicates previously thought to be indigenous to Europe and the Americas are, in fact, invaders. Some of these invasions may have occurred centuries or even millennia ago. In some areas, tunicates are proving to be a major threat to aquaculture operations.

The U.S. Geological Survey, NOAA Fisheries, and the University of Rhode Island are investigating this phenomenon as they have been spotted in 2004 in Georges Bank. They requested that any information or sightings of these invading colonies be reported to United States Geological Survey to aid in their investigation.