Accumulation of manganese in the haemolymph, nerve and muscle tissue of Nephrops norvegicus (L.) and its effect on neuromuscular performance

Exposure of Norway lobsters, Nephrops norvegicus (L.) for 3 weeks to manganese concentrations, (5 & 10 mg Mn l(-1) (90-180 microM)), led to its accumulation in various body tissues. The highest concentration was in nerve tissue (brain and abdominal ganglia) which had up to 6 times (on wet wt. basis) the manganese concentration of the exposure concentration, whereas the haemolymph accumulated 3 times and the muscle tissue only 0.5 times the exposure concentration. In the haemolymph the manganese was bound mainly to protein, predominantly (80-90%) to the respiratory protein haemocyanin, as the concentration was 14 times higher in the protein fraction than in the supernatant. Manganese did not substitute for copper in the haemocyanin, as the copper concentration remained constant despite the manganese exposure. The possibility that manganese exposure induced neurotoxic effects sufficient to reduce neuromuscular performance was assessed from the kinematics of free tail-flip swimming, and from measures of the forces produced by abdominal movements in tethered animals. No significant reduction in tail flip velocity or flexion force, but a significant reduction in the maximum post-flip extension force was found. No correlation was found between the manganese concentration in a single tissue or different fractions of the haemolymph and the post-flip extension, except for a weak negative correlation with the manganese concentration in the abdominal ganglion. The ecophysiological implications of these results are discussed.