Influence of salinity and suspended matter on benthos of an Arctic tidal flat

An Arctic tidal Bat in Spitsbergen (Svalbard Archipelago) was studied along a transect from the river on the landward side to the adjacent fjord in Ju ly 1996 and 1997. The concentration of suspended particulate matter ranged From 500 mg I-1 in the river to 50-200 mg I-1 over the tidal flat and to le ss than 20 mg I-1 in the surface water of the fjord. Sedimentation rates ra nged from 10 g m(-2) d(-1) close to the river mouth to 60 g m(-2) d(-1) on the tidal Rat and reached maximum values of over 500 g m(-2) d(-1) just acr oss the tidal Bat break, characterized by a sharp salinity and depth gradie nt. Macrozoobenthos biomass increased from 1 g ww m(-2) in the tidal Bat to over 50 g ww m(-2) in the fjord basin. The number of macrobenthos species increased from 3 to 70 across the steep depth/salinity gradient. Diversity was little different between stations exposed to heavy and low sedimentatio n in the fjord. The critical zone of environmental change appears to be ver y narrow and is situated just on the tidal shelf break, where zoobenthos ch anges as sharply as the salinity/depth gradients. (C) 1999 International Co uncil for the Exploration of the Sea.