Iceland: a laboratory for non-indigenous ascidians

Abstract

Non-indigenous species (NIS) represent a serious problem worldwide, where ascidians are one of the most important taxa. However, little has been done to document the non-indigenous ascidians in Iceland, and over the past decade only two species had been recorded prior to the present study, Ciona intestinalis in 2007 and Botryllus schlosseri in 2011. To increase the knowledge of this taxon, extensive sampling was carried out in shallow waters around Iceland, during the summer 2018, in ports and on ropes of a long-line mussel aquaculture. In total, eleven species were identified, four native and seven NIS, of which Diplosoma listerianum, Ascidiella aspersa, Botrylloides violaceus, Molgula manhattensis and Ciona cf. robusta, are now reported for the first time in Iceland. The highest abundance of non-indigenous ascidians appeared among the ports in southwestern Iceland (Sandgerði, Hafnarfjörður). As pointed out for other regions, the most likely vector is maritime traffic (hull fouling and ballast water), although other vectors cannot be ruled out. The future expansion of these non-indigenous ascidians around Iceland must be monitored, where local maritime traffic could play an important role. Furthermore, global warming may facilitate the access and establishment of these species in colder areas with arctic influence (north and east of Iceland), which are likely still free of these species.