The distribution of juvenile benthic invertebrates in an arctic glacial fjord

Abstract

The distribution of juvenile benthic invertebrates with respect to their abiotic environment was investigated at four locations along a gradient in Kongsfjorden (79°N, 12°E), Spitsbergen, in September 1997. Heavy discharge of inorganic sediments released by the three glaciers was expected to be one of the main structuring factors of benthic communities in the fjord. Juveniles of 76 species/families are identified. Total abundance increases with distance from the fjord head due to the dominance of opportunistic polychaetes, while diversity is highest close to the glacier. Juvenile polychaetes are the most abundant taxon over all stations (92%), followed by bivalves, crustaceans and others. Polychaetes also provide most species (55%) and are the dominant taxon at every station. Their abundance is highly correlated with total organic carbon, indicating that most of them are deposit feeders. Young crustaceans rapidly decrease towards the fjord mouth, probably due to stronger bottom currents. Even though young oligochaetes are exclusively found near the glacier, no species seem to be well adapted to the high sedimentation rate close to the glacier. Juvenile suspension-feeding bivalves seem to be less disturbed by glacial discharge but appear to be more vulnerable to currents on the more exposed sites. The importance of deposit feeders and carnivores increases towards the outer stations. Non-metric multidimensional scaling confirms the distinct gradient in community composition along the fjord. Coupling the biotic data to abiotic factors (depth, bottom-water salinity, bottom-water temperature, sediment grain size and sedimentation rate) using canonical correspondence analysis revealed that hydrographic factors are more responsible for the structuring of the benthic juvenile community at the shallow stations close to the glacier (except the station directly at the glacier). At the outer deeper stations, sediment grain size and related properties may play a more important role.