PARTITIONING OF BENTHIC COMMUNITY RESPIRATION IN THE ARCTIC (NORTHWESTERN BARENTS SEA)

For marine benthos communities, the assessment of a respiration budget encompassing the entire size range from microbes to mobile megafauna has seldom been attempted. An interdisciplinary field study in high Arctic waters (northwestern Barents Sea) in June/July 1991 provided the opportunity to concurrently estimate the oxygen uptake of the different benthic community fractions by a variety of approaches at water depths of 80 to 1010 m. The bulk respiration of micro-, meio- and small macrobenthos was assessed by sediment community oxygen consumption (SCOC) rates measured by shipboard sediment-water incubations of virtually undisturbed cores. The oxygen uptake of community portions not sampled adequately by corers (megabenthic in- and epifauna, including fish) was estimated by applying individual metabolic rates to density or biomass figures derived from seabed images, box corer samples or trawl catches. The respiration estimates of the various community fractions were subsequently compiled in synoptic models of the total benthic community oxygen consumption (BCOC) and its partitioning. In the study area, 2 benthic habitat types were distinguished, differing substantially in depth, sediment texture and, thus, benthic respiration pattern: (1) shallow shelf banks (<200 m) where the seabed is composed of coarse sediments and stones, and (2) deeper trenches or slopes (>200 m) characterized by fine sediments. On the banks, the patchiness of epibenthic brittle stars, which locally occurred in very high densities (up to 700 ind. m(-2)), controlled the benthic community respiration. On average, the megafauna was estimated to contribute about 25% to the median BCOC of about 90 mu mol O-2 m(-2) h(-1) (equivalent to an organic carbon mineralization rate of 21 mg C m(-2) d(-1)). In the shelf trenches and on the slope, however, smaller endobenthic organisms predominated. SCOC, according to our estimates of meio- and macrofaunal respiration, was dominated by the oxygen uptake of microorganisms and accounted for about 85% of the median BCOC of about 140 mu mol O-2 m(-2) h(-1) (35 mg C m(-2) d(-1)). Our results suggest that current models of benthic community respiration should be amended, particularly for Arctic shelf biotopes where abundant megafauna may represent an important pathway of the benthic energy flow.