Numerous definitions exist for "the Arctic", largely based on political boundaries. For the purposes of ArcOD’s effort, we define the regions based on biologically relevant physical criteria: areas within the seasonally-averaged 2°C surface isotherm or the median maximum sea-ice extent (whichever is greater). For deep-sea pelagic and benthic communities cold Arctic water occurs through the entire Norwegian Sea bounded largely by a deep-sea ridge running form Greenland, through Iceland and the Faroe Island to southern Norway. The boundaries should not be considered absolute, because they shift seasonally, and indications are they have been shifting over the past century. Seasonally, there are large influxes of species from outside of the Arctic into it as part of the cycle that has existed for centuries. Larger more mobile species migrate back out, but for many invertebrates transport into the Arctic is a one-way path that effectively removes them from the species’ reproductive pool.

Despite more than a century of study, there is no pan-Arctic list of all the species living in the Arctic Ocean and the adjoining Sea. Until now the most complete list was the 2001 List of species of free-living invertebrates of Eurasian Arctic Seas and adjacent deep waters, edited by Boris Sirenko from the Zoological Institute in St. Petersburg, Russia. Using this list as a starting point, we have added the known marine vertebrates, and species within the databases currently assembled by the Arctic Ocean Diversity (ArcOD) project, and aligned them with the World Register of Marine Species (WoRMS) who maintain such registers.

The list currently includes all multicellular animals. We are now turning our attention to adding the phytoplankton, macrophytes and eucaryotic protists into the next release, as well as updates to the list based on ArcOD's underway synthesis activities. The next version will also include information on habitat (benthic or pelagic, depth preferences).

Like all such lists, it is an evolving process as new species are added, some are shown to be invalid (or misidentified), and some species are recognized as synonymous with other names by ArcOD and WoRMS taxonomic editors. The ARMS editorial board maintains these registers but is aware that they may not be complete and may contain errors. The board cannot be held responsible for any errors or misuse of data contained in these registers. Comments from our users are more than welcome, so if you come across incorrect or incomplete information, or you are willing to contribute to this initiative, please contact rrhopcroft@alaska.edu.

The ARMS editorial board consists of taxonomic and data management experts. It relies heavily on the established board of editors to establish the validity of species. Distribution records for names listed in the ARMS database have been or are being checked and updated by ARMS taxonomic experts. The ARMS editorial board does not directly have the authority to modify taxonomic information stored in WoRMS; however, the editors may collaborate with WoRMS taxonomic editors to effect changes.