An aggressive, invasive aquatic organism that is on the state’s most dangerous species list has been discovered in both Winchester Bay and Coos Bay, and scientists say this “colonial tunicate” – Didemnum vexillum – has serious economic and environmental implications.

Its propensity to foul surfaces of boats, fishing nets, water intakes, docks and buoys could make it costly to control, and its ability to smother shellfish beds and sensitive marine environments threatens other marine life.

“This is not a welcome addition to our bays and now the clock is ticking,” said Sam Chan, Oregon Sea Grant’s  invasive species specialist at Oregon State University and chair of the Oregon Invasive Species Council. “The fouling potential from tunicate invasions can be severe, given its ability to reproduce asexually by budding, or breaking off as fragments, and through sexual reproduction where tadpoles emerge, swim and attach themselves to surfaces to form new colonies.”

The Didemnum invertebrates were first discovered earlier this year  in Winchester Bay, and later in Coos Bay. They are native to Japan and can live from the estuary to the continental shelf. In calm water, colonies may grow in long, beard-like expanses on substrates such as docks, mooring lines, boat hulls and aquaculture infrastructure.

In faster currents, Didemnum forms low, undulating mats overgrowing seabeds of pebbles, boulders and jetty rock. The organisms will grow over, and choke clams, oysters, mussels, anemones and other marine creatures by covering their feeding siphons, and can serve as a barrier between bottom-feeding fish and their prey.
Read more …