Intraspecific variation in the responses to copper by two estuarine invertebrates
Copper tolerance has been investigated in Nereis diversicolor and Corophium volutator from three different estuaries; the Humber, Alaw and Dulas, and intraspecific variation in the responses to copper of both these animals were examined. Sediment concentrations of copper from Dulas were the highest (224µg g⁻¹) compared to the Humber (70µg g⁻¹) and Alaw (6.2µg g⁻¹) estuaries. A high ability to tolerate copper based on 96 hour LC₅₀ values for dissolved copper (1.75 mg l⁻¹ in Corophium and 0.59mg l⁻¹ in Nereis) and high body copper concentrations (450µg g⁻¹ in Corophium and 698µg g⁻¹ in Nereis) were found in animals from the Dulas estuary. Moderate tolerance (1.34mg l⁻¹ in Corophium and 0.34mg l⁻¹ in Nereis) and moderate body copper concentrations (140µg g⁻¹ in Corophium and 100µg g-1 in Nereis) were found in species from the Humber, compared to animals from the Alaw which showed very low copper tolerance (0.8mg l⁻¹ in Corophium and 0.26mg l⁻¹ in Nereis) with very low body copper concentrations (52µg g⁻¹ in Corophium and 65µg g⁻¹ in Nereis). These copper concentrations and degree of tolerance in Corophium and Nereis from the three estuaries reflected the levels in the sediments. Tolerance could not be acquired after exposure of juvenile and adult Nereis to a range of sublethal copper concentrations over a 30 day period. Tolerance in adult worms from Dulas was not lost after exposure to 'clean' conditions for 30 days supporting the suggestion that it may be genetic. In the Humber estuary there was generally little spatial or temporal variability shown in a suite of metal concentrations in the sediments, Corophium and Nereis recorded at 3-monthly intervals over a 12 month period. Interspecific and intraspecific differences were found in the uptake and accumulation of copper. Copper tolerant Corophium accumulated significantly lower amounts of copper (relative to their control concentrations) compared to the less tolerant populations after exposure to external dissolved copper concentrations. The opposite was true for the tolerant population of Nereis accumulating the highest amount of copper relative to their control levels. The high levels of total body copper found in the tolerant populations of both Corophium and Nereis suggests that the metal is being sequestered in a non-toxic way, but an exclusion mechanism and/or an excretion mechanism may also be in operation. Localisation of this metal was investigated in the tolerant population of Nereis and the accumulated copper was found to be tissue specific. The ability to tolerate copper was probably due to increased deposition of copper in membrane-bound structures located in the cells of the nephridial tubules. Copper was not found in the nephridial area of the non tolerant worms from the Alaw estuary. Intraspecific variation was found to occur in the survival and body copper concentrations of Corophium and Nereis after exposure to different natural sediments in experimental situations. The physicochemical nature of each of the sediments affected the bioavailibity of copper which caused different responses in Corophium and Nereis. Patterns and similarities between the biological responses and physico-chemical parameters were examined and simple predictive models were constructed to explain the variation found in the responses of Corophium and Nereis. The LC₅₀ value was used as an index of tolerance and was found to be important in explaining variation in the survival and copper accumulation in Corophium and Nereis. These results were used to discuss the importance of intraspecific variation in Corophium and Nereis in the monitoring and management of metals in estuaries. This would produce sensitive and responsive management tools for individual estuaries rather than a blanket approach. This may be appropriate in some situations, particularly where certain metals are problematical as with the case of copper in the Humber estuary.