Manganese Uptake and Lethality in the Sea Star Asterias rubens: Effect of Hypoxia.

Oxygen depletion due to eutrophication in marine waters has been an increasing problem worldwide and during oxygen depletion events, benthic organisms may concurrently be exposed to hypoxia and manganese leaching from reduced sediments. In this investigation the uptake and toxic effects of manganese under normoxia and hypoxia were studied in the sea star Asterias rubens. Exposure to 1 mg Mn L^-1 for 4 weeks resulted in increased manganese concentrations in tube feet and pyloric caeca, whereas the concentrations in the aboral body wall showed no statistically significant changes. Manganese concentrations and accumulation did not differ between hypoxia (25% oxygen saturation) and normoxia; mortality was not observed in either of these exposure scenarios. Exposure to 0, 25, 35 and 50 mg Mn L^-1 resulted in a time and concentration dependent increase in mortality over 7 d, aggravated by hypoxic conditions. Hypoxic conditions significantly reduced average survival time at exposure to 50 mg Mn L^-1.