Evaluating the interaction of the invasive tunicate Didemnum vexillum with the Atlantic sea scallop Placopecten magellanicus on open and closed fishing grounds of Georges Bank.

An invasive colonial tunicate (Didemnum vexillum) was initially observed on Georges Bank in 1998, and it has since spread in benthic environments on fishing grounds and areas closed to bottom-fishing. It can form dense mats on gravel substrates that are also a preferred habitat for the Atlantic sea scallop (Placopecten magellanicus), which supports one of the most valuable commercial fisheries in the United States. We used HabCam, a vessel-towed underwater imaging system, to investigate the spatial distributions of P. magellanicus and D. vexillum in a region that includes fishing grounds and an area protected from bottom-fishing. We found a negative relationship between P. magellanicus and D. vexillum, even after controlling for substrate and management status, suggesting that D. vexillum competes for habitat with P. magellanicus. We also applied the geostatistical method of universal kriging to interpolate the distribution of D. vexllium based on the covariables gravel, depth and area. Our results indicate that D. vexillum is more common in areas open to fishing than in the areas closed to fishing, even taking bottom substrate effects into account. Didemnum vexillum appears to have spread over portions of the northern edge of Georges Bank. This research evaluates potential fish and invertebrate habitat degradation caused by an invasive species. [ABSTRACT FROM AUTHOR]