Discovery and significance of the colonial tunicate <I>Didemnum vexillum</I> in Alaska

Abstract

The colonial tunicate, Didemnum vexillum Kott, 2002, has a history of invading and overgrowing marine communities in temperate waters worldwide. The species can colonize and dominate remarkably large areas of benthic habitat, including coastal bays and outer coastal areas, causing concerns about potential long-term effects on community structure, critical habitats, and fisheries resources. We report here the confirmed occurrence of D. vexillum in Alaska, representing a dramatic 1000 km northward extension of this non-native species along the western coast of North America. The species was detected as part of a &quot; bioblitz&quot;, engaging citizen scientists to survey local biota and detect non-native marine species incursions. Following detection, the identity of D. vexillum was confirmed with robust genetic methods, and morphological characters were also consistent with previous species descriptions. Although invasions have been relatively rare in Alaskan waters to date, it is now clear that D. vexillum is established in at least one site (Whiting Harbor) near Sitka, Alaska. Given the explosive growth and spread of this species in other global regions, and its potential for significant impacts across diverse habitats in Alaska, current efforts are underway to evaluate its distribution and options to eradicate or control the species.