Distribution and diversity of desmosomatid and nannoniscid isopods (Crustacea) on the Greenland-Iceland-Faeroe Ridge

The distribution and diversity of isopods (Crustacea, Isopoda; families Desmosomatidae Sars, 1897 and Nannoniscidae Hansen, 1916) was examined in Icelandic waters where a diversity of water masses (temperature range -0.9 to 12°C) occurs and the topography is characterized by the large and shallow Greenland-Iceland-Faeroe (GIF) Ridge extending across the North Atlantic in an east-west direction. Both families were species rich in the area, in total occurring with 34 species in 20 genera. Most of the species were restricted either to the north (10) or to the south (14) of the GIF Ridge, occurring either in cold (-0.8 to 2.8°C) or warm (>2°C) water masses. Five species were found on both sides of the Ridge, occurring at a wide range of temperatures (-0.9 to >4°C), while another five species extend across the GIF Ridge. Most species occurred in two and more water masses and the species north of the Ridge occurred usually within narrower temperature range than the species living south of the Ridge. The water masses in association with the Ridge seem to limit distribution of most species. Despite similar number of species occurring in the areas north and south of the Ridge, the areas differ considerably in diversity pattern with depth.