Uptake of diatoms in Baltic Sea macrozoobenthos during short-term exposure to severe and moderate hypoxia

Abstract

The effect of severe and moderate hypoxia on food uptake of benthic macrofauna was studied in the laboratory. The hypothesis was that low oxygen concentrations negatively affect feed- ing at oxygen levels that have little effect on the studied animals' survival. The bivalve Macoma balthica, the priapulid Halicryptus spinulosus, the amphipods Monoporeia affinis (subadult & juve- nile) and Pontoporeia femorata (subadult) were offered the 14 C-labelled diatom Skeletonema costa- tum in 0.8 to 10.6 mg O2 l -1 . Feeding was measured as radioactivity uptake. Subadult amphipods were studied one species at a time (single) or together (mixed). Feeding changed in all amphipods at the lowest oxygen concentrations, but no effect was found for M. balthica and H. spinulosus. At the lowest concentration (0.8 mg O2 l -1 ) feeding by subadult M. affinis (single) was only 17% of the full oxygen saturation (10.6 mg O2 l -1 ), and, at 1.6 mg O2 l -1 , 14% of the feeding at 8.9 mg O2 l -1 . Juvenile M. affinis consumed more labelled algae at 3 mg O2 l -1 than at higher oxygen concentrations. M. balthica feeding was not affected. Little radioactivity uptake was registered for H. spinulosus at any oxygen concentration, showing that H. spinulosus is not a surface deposit feeder. The amphipods were the most sensitive to week-long oxygen deficiency. Survival decreased significantly in the lowest oxygen concentrations (0.8; 1.6 mg O2 l -1 ). Of the subadult M. affinis 15 and 65%, respectively, survived, compared with 0 and 58% for P. femorata. Juvenile M. affinis mortality was high in all oxygen concentrations, whereas most M. balthica and H. spinulosus survived.