Stable macrofauna community structure despite fluctuating food supply in subtidal soft sediments of Oslofjord,Norway

At a locality at 32-m depth in Oslofjord, Norway, temperature varied from 4.8° to 9.2°C and salinity varied from 31.2 to 33.3 S over a two-year period. There was a peak in chlorophyll a, and C and N in April–June and a smaller peak in November in the sediment. Bacterial numbers showed maxima in July–August and November–December. The macrobenthic fauna was typical of a species-rich and undisturbed boreal community of silt-clay sediments. The community was predominantly composed of surface and subsurface deposit feeders. Over the twoyear period there was little variation in numerical abundance or biomass of the species despite the variation in food input. The lack of seasonality shown by the fauna probably relates to the lack of variability of the physical environment. The mechanism by which this control is achieved, however, is not known. There are large predators/disturbers in the community such as the polychaetes Lumbrineris fragilis, Glycera rouxii, G. alba, Nephthys spp. and the echinoid Brissopsis lyrifera, which probably play an important role in structuring the community.