OCCURRENCE OF THE BENTHIC TRACHYMEDUSA PTYCHOGASTRIA-POLARIS ALLMAN, 1878 (CNIDARIA, HYDROZOA) OFF NORTHEAST GREENLAND AND IN THE NORTHERN BARENTS SEA

The trachymedusa Ptychogastria polaris Allman, 1878 has been identifie d in seabed photographs from high-Arctic shelves and upper continental slopes off Northeast Greenland and in the northern Barents Sea. It wa s found to be a common epifaunal element, being present at 34 of 57 st ations in 40- to 495-m depth and at 7 of 11 stations in 70- to 330-m d epth, respectively. All specimens recorded in the photographs either s at directly at, or hovered very closely (less than or equal to about 1 cm) over, the sea bed, indicating a primarily epibenthic life style o f this hydrozoan species. The small-scale (i.e. within-station) distri bution of medusae was rather patchy, with frequencies along photograph ic transects consisting of 35-73 pictures distributed over seabed stri ps of 150- to 300-m length - varying from 1 to 58% off Northeast Green land and from 1 to 34% in the Barents Sea. Absolute maximum density wa s 6 ind m(-2), and station mean abundances ranged from 0.01 to 0.91 in d m(-2) and from 0.01 to 0.52 ind m(-2), respectively. Values tended t o decrease with water depth, albeit significantly only off Northeast G reenland. Otherwise, no clear relationships to environmental condition s, such as geomorphology or near-bottom water hydrography, were detect ed. Circumstantial evidence suggests that seabed granulometry and pote ntial food supply are important distribution determinants. However, fu rther investigations are required to identify more stringently the key factors controlling the distribution of P. polaris.