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Since the discovery of the invasive colonial tunicate Didemnum vexillum Kott, 2002 on Georges Bank in 2002, research has focused on investigating the spread of the tunicate invasion, evaluating its potential impact on the benthic community, identifying it to species level, and determining its region of origin. The percent cover of Didemnum vexillum, measured from bottom photographs, ranges from 0-100% in individual photos and between 0-79% when averaged within photo transects. Individual photos represent an area of the seabed measuring ~ 0.39 m2 while photo transects range from ~ 700-1000 meters in length. Hydroids are the second most abundant epifaunal taxon. The macrofauna identified in bottom photo analysis comprises 21 different taxa, of which burrowing and non-burrowing anemones are the most numerous. Our detailed analysis of bottom photographs suggests that Didemnum vexillum is able to out-compete other epifaunal and macrofaunal taxa. An Analysis of Similarity (ANOSIM) test on macrofauna abundance data collected with a Naturalist dredge from 1994 to 2006, indicates that Didemnum vexillum has had a significant impact on the species composition of the benthic community. The abundance of two polychaete species, Nereis zonata Malmgren, 1867 and Harmothoe extenuata Grube, 1840, increased significantly in infested areas compared with uninfested areas, according to two-way Analysis of Variance (ANOVA). We found four distinct nucleotide sequences of the 18s rDNA gene among 17 samples of Didemnum species, three from Georges Bank and one from New Zealand. Two of the Georges Bank sequences were identified as Didemnum albidum Verrill, 1871, a species native to the northeast United States. The third sequence represents the invasive Didemnum vexillum from Georges Bank, and the fourth sequence an undescribed species from New Zealand (not D. vexillum).

Publication Title, e.g., Journal

Proceedings of the 2nd International Invasive Sea Squirt Conference





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This work is licensed under a Creative Commons Attribution 4.0 License.