UPTAKE, ACCUMULATION AND REGULATION OF MANGANESE DURING EXPERIMENTAL HYPOXIA AND NORMOXIA BY THE DECAPOD NEPHROPS-NORVEGICUS (L)

A consequence of eutrophication in marine coastal waters is the increased oxygen demand of the sediments. This has resulted in repeated autumnal hypoxia of the bottom waters in many areas and an enhanced flux of manganese (Mn) from the sediment to the overlying waters. Manganese accumulation, subsequent uptake and regulation in the Norway lobster, Nephrops norvegicus, have been investigated, Nephrops norvegicus were continuously exposed for 2 weeks to 555, 1755 and 5555 mu g l(-1) manganese in combination with hypoxia (2.8-3.2 kPa) or normoxia. Net accumulation occurred in animals exposed to concentrations of 1755 mu g l(-1) Mn and higher, Accumulation was greatest in gills and haemolymph and least in muscle tissue. The oxygen level had no effect on the accumulation of bioavailable manganese or copper distribution in any tissue of N. norvegicus. In short term experiments using labelled manganese (Mn-54) lobsters were exposed to 100 mu g Mn l(-1) for up to 72 h. The results confirmed that haemolymph and gills were the main target tissues. Urine Mn excretion after pre-exposure to 100 mu g Mn l(-1) was constant in animals allowed to excrete into clean water for an additional 5 days.