High carbon demand of dominant macrozoobenthic species indicates their central role in ecosystem carbon flow in a sub-Arctic fjord

摘要

ABSTRACT: The sea urchin Strongylocentrotus droebachiensis and the scallop Chlamys islandica dominate the shallow macrobenthic community in Kobbefjord, southwest Greenland (64°09’N, 51°36’W). Densities were estimated from seafloor photographs along 3 depth transects (0 to 120 m). Annually formed growth bands in the interambulacral plates of S. droebachiensis and in the ligament of C. islandica were used to establish growth functions. Growth data combined with size frequencies, size–mass relationships and fjord bathymetry were used to estimate annual production and carbon demand of the 2 species in order to assess their ecological importance. Distributions of the 2 species were strongly related to depth and partially separated. Averaged over all depths, the densities were estimated at 4.9 ind. m–2 (range: 0 to 38 ind. m–2) and 5.6 ind. m–2 (range: 0 to 57 ind. m–2) for S. droebachiensis and C. islandica, respectively. Maximum ages of S. droebachiensis and C. islandica were estimated at 24 and 39 yr, respectively. Somatic growth of both species was relatively slow, and their reproductive output constituted the bulk (62 to 73%) of their total annual production. Mean annual production in the fjord was estimated at 3.2 g ash-free dry weight (AFDW) m–2 for S. droebachiensis and 2.5 g AFDW m–2 for C. islandica. The total annual carbon demand of the 2 species was estimated at 30.6 g C m–2, corresponding to 21–45% of annual pelagic primary production in this area. In conclusion, S. droebachiensis and C. islandica play important roles in carbon cycling of Kobbefjord and can be regarded as central species of the shallow benthic community. A comparison with literature estimates of annual macrozoobenthic carbon demand in Arctic and sub-Arctic habitats revealed that the macrozoobenthic carbon demand in Kobbefjord is relatively high and that annual carbon requirements of macrozoobenthos in the Arctic seem to reflect the level of pelagic primary production.