Marine invertebrates in the Arctic 27 November 2014 This article is part of a series highlighting issues from the Conservation of Arctic Flora and Fauna (CAFF) working group’s landmark Arctic Biodiversity Assessment. This week focuses on Arctic marine invertebrates. Of the roughly 5,000 known Arctic marine invertebrates, more than 90% occur in the benthic realm (the region on, near, or just beneath the sea floor on the continental shelf). The dominant group is crustaceans (species such as crabs, lobsters and krill), with nearly 1,500 species in the Arctic. Other important groups include molluscs (such as squid, octopus, snails, clams and mussels), annelids (segmented worms), and bryozoa (“moss animals”). Species richness is highest in the Chukchi Sea, the Barents Sea and the Kara Sea. Like other organisms in the Arctic, marine invertebrates are likely affected by climate warming, and some effects are already documented along the margins of the Arctic Ocean. Major effects of warming are anticipated on those species that depend on sea ice, and which will therefore lose their habitat as ice disappears. However, overall, global warming is not expected to drastically reduce marine invertebrate species diversity, because much of the Arctic Ocean’s marine invertebrate diversity is made up of species that originate further south and are not unique to the Arctic. On the contrary, there may be increased diversity due to the northward immigration of species from warmer waters further south. As would be predicted, this “borealization” has so far occurred in the margins of the Arctic Ocean, primarily at the two major gateways of the Atlantic and Pacific. In the long term, such migration may eventually lead to a new interchange of species across oceans. Vast areas of the Arctic Ocean have not been comprehensively sampled, so the list of “known species” is expected to grow. In particular, the western Arctic had been poorly sampled until the last few decades, and the Lincoln Sea (which lies north of the Nares Strait) is the least-studied large marine area in the Arctic. It is covered with sea ice year-round. There are exceptions such as the Barents Sea, which has a long history of studies lasting over 100 years. Indeed, the simple fact that it is so much better-studied than many other regions may explain the greater diversity of species that have been identified, in comparison with other marine regions of the Arctic. Click here to read more in the “Marine Invertebrates” chapter of the ABA, written by lead authors Alf B. Josefson and Vadim Mokievsky For more biodiversity graphics, please visit the Arctic Biodiversity Data Service: www.abds.is Photo: Tetsushi Tsunemi / Creative Commons BY-NC-SA / Clione Limacina.