Measurement of physiological energetics (scope for growth) and chemical contaminants in mussels ( Arca zebra) transplanted along a contamination gradient in Bermuda

Abstract

Mussels ( Arca zebra) were transplanted to two sites in Castle Harbour and five sites along a contamination gradient in Hamilton Harbour, Bermuda. After 11–12 days mussels were sampled for measurement of physiological responses (such as feeding rate, food absorption and respiration rate) and analysis of chemical contaminants in their body tissues (metals, alkyltins, hydrocarbons and their polar oxygenated derivatives and polychlorinated biphenyls). Physiological responses were integrated by means of the energy balance equation and performance was assessed in terms of “scope for growth”. Mussels sampled 50 m from the Castle Harbour “dump site” showed a slight, but not significant ( P > 0.05), decline in scope for growth and a slight increase in accumulated contaminants (tributyltin, petroleum hydrocarbons and PCBs) in comparison with the Castle Harbour “reference site”. In contrast, mussels sampled from sites along the length of Hamilton Harbour showed a marked decline in scope for growth ( P < 0.05), due to a reduction in feeding rate and an increase in metabolic energy expenditure. This was accompanied by a significant accumulation of contaminants (Pb, tri- and di-butyltin, petroleum hydrocarbons and their polar oxygenated derivatives and PCBs). There was a significant negative correlation between the scope for growth of Arca and the concentration of Pb ( r = −0.76), TBT ( r = −0.91), aromatic hydrocarbons ( r = −0.92) and PCBs ( r = −0.95) in their tissues. Arca accumulated petroleum hydrocarbons and their polar oxygenated derivatives to tissue concentrations that were sufficient to explain the recorded decline in feeding rate, through the mechanism of “nonspecific narcosis” (based on relationships established for the mussel, Mytilus edulis). Similarly, tributyltin was accumulated to concentrations that could induce the observed increase in energy expenditure, through the mechanism of uncoupling of oxidative phosphorylation. Toxicological interpretation of the coupled physiological and tissue residue chemistry data therefore indicates that petroleum hydrocarbons and tributyltin are the major toxic contaminants causing the reduction in scope for growth of Arca in Hamilton Harbour.