A PHOTOGRAPHIC SURVEY OF THE EPIBENTHIC MEGAFAUNA OF THE ARCTIC LAPTEV SEA SHELF - DISTRIBUTION, ABUNDANCE, AND ESTIMATES OF BIOMASS AND ORGANIC-CARBON DEMAND

The epibenthic megafauna of the high-Arctic Laptev Sea shelf was inves tigated in August/September 1993 and October 1995. At 13 stations in w ater depths of between 14 and 45 m, series of 5 to 29 photographs, eac h depicting about 1 m(2) of the seabed, were taken to assess epifaunal distribution patterns and abundances. Furthermore, population biomass of dominant brittle stars was estimated by combining abundance values with size-mass relationships and size frequencies established by meas uring specimens on scaled photographs. A total of 13 epibenthic specie s were identified. Species numbers per station were low, ranging betwe en 1 and 6. Total epibenthic abundances, averaging 173.7 ind. m(-2), r anged considerably between 0.1 and 579.5 ind, m(-2). Except for some s tations on shallow shelf banks <20 m that were characterized by bottom -water salinities <30 due to fluvial dilution, the brittle star Ophioc ten sericeum dominated the megabenthic shelf assemblages. At the flank s of sunken Pleistocene river valleys in depths >30 m, it reached maxi mum density and biomass values of 566 ind, m(-2) and 1.5 g ash-free dr y mass (AFDM) m(-2), respectively. At some sites, the brittle star Oph iura sarsi occurred in abundances of up to 35 ind. m(-2) and attained a biomass of 3.8 g AFDM m(-2). Of local importance were the sea cucumb er Myriotrochus rinckii (up to 70 ind. m(-2)) and the bivalve Arctinul a greenlandica (up to 33 ind. m(-2)). All other species were recorded with distinctly lower densities (less than or equal to 1 ind. m(-2)). Gross estimates of population respiration and production of dominant b rittle stars suggest that their organic carbon demand may amount to a pooled average of about 4 mg C m(-2) d(-1) in the Laptev Sea, locally even to a maximum of >10 mg C m(-2) d(-1). This finding indicates that a substantial portion of the energy flow in this high-Arctic shelf ec osystem may be channelled through dense brittle star assemblages.