A photographic survey of the epibenthic megafauna of the Arctic Laptev Sea shelf:distribution, abundance, and estimates of biomass and organic carbon demand

Abstract

The epibenthic megafauna of the high-Arctic Laptev Sea shelf was investigated in August/September 1993 and October 1995. At 13 stations in water depths of between 14 and 45 m, series of 5 to 29 photographs, each depicting about 1 m2 of the seabed, were taken to assess epifaunal dis t r~but~on patterns and abundances. Furthermore, population biomass of dominant br~ttle stars was estimated by combining abundance values with size-mass relationships and size frequencies established by measuring specimens on scaled photographs. A total of 13 epibenthic species were identified. Species numbers per station were low, ranging between 1 and 6. Total epibenthic abundances, averaging 173.7 ind. m-2, ranged considerably between 0.1 and 579.5 ind. m-2 Except for some stations on shallow shelf banks 30 m, it reached maximum density and biomass values of 566 ~ n d . m-2 and 1.5 g ash-free dry mass (AFDM) m ', respectively. At some sites, the brittle star Ophlura sarsi occurred in abundances of up to 35 ind. m-' and attained a biomass of 3.8 g AFDM m-2 Of local importance were the sea cucumber Myrjotrochus rinckii (up to 7 0 ind. m-') and the bivalve Arctinula greenlandica (up to 33 ind. m-2). All other species were recorded with distinctly lower densities (S1 ind. mT2). Gross estimates of population respiration and production of dominant brittle stars suggest that their organic carbon demand may amount to a pooled average of about 4 mg C m-' d-' in the Laptev Sea, locally even to a maximum of >l0 mg C m-2 d-' This finding indicates that a substantial portion of the energy flow in this high-Arctic shelf ecosystem may be channelled through dense brittle star assemblages.