No abstract

Abstract. Eutrophication has been reported for autumn months in regions of the Kattegat/Skagerrak, causing stress to bottom-living organisms. The present studies, undertaken in April (1989), investigated the effects of hypoxia and high ammonia levels in the burrowing decapod Nephrops norvegicus (L.). The net ammonia efflux rates and circulating ammonia levels at 6 and 12°C, at normoxia [partial pressure of 02 in the water (torr), Pw02 = 155 torr)] and hypoxia P, vO2 = 24 torr) in normal seawater and ammonia-enriched (300 #mol ammonia 1-t) seawater were examined. The hourly weight-specific efflux rates were very variable and in all groups included some individuals which showed periods of no net efflux, or even a net uptake of ammonia. At each temperature, net efflux-rate differences due to treatments were not significant (P>0.05; ANOVA, in all cases) and only the differences between the net efflux rates of the normoxic groups were significantly affected by temperature (P < 0.05; ANOVA). Circulating ammonia levels were also variable, and at 6°C the ammonia-enriched groups had significantly higher weight-specific blood ammonia content values than the normoxic group (P < 0.05 in both cases). A net uptake of ammonia occurred in ammoniaenriched conditions -probably along a reversed NH4 + gradient, as downhill pNH 3 gradients were maintained in all groups -and may represent the only means by which some branchial efflux of ammonia could proceed.