Experimental studies on the effects of copper on a marine food chain

Abstract

Effects of copper sulphate on a marine food chain were investigated in large tanks at Loch Ewe on the west coast of Scotland. The food chain consisted of phytoplankton, the bivalve Tellina tenuis da Costa, and O-group plaice (Pleuronectes platessa L). During initial months after settlement, T. tenuis siphons are an important food for juvenile plaice, which feed by grazing the siphon tips; these subsequently regenerate. Copper dose rates of 10, 30 and 100 μg Cu/1 were investigated; the distribution of added copper was monitored and its metabolic effects were determined. Copper levels in water, sand, in algae on tank walls, in T. tenuis shell and flesh, and in plaice muscle and viscera were measured by atomic absorption spectrophotometry. Copper accumulated in sand, T. tenuis flesh and shell, and plaice viscera. Accumulations were dose-dependent and in no case was a plateau concentration reached. Most of the added dose was taken up by the sand; accumulations in T. tenuis shell were small — less than twice background in all cases. High levels were found in T. tenuis flesh, where concentrations after 100 days were 270, 470 and 1100 μg Cu/g dry flesh for dose concentrations of 10, 30 and 100 μg Cu/1, respectively. The mean control concentration was less than 50 μg Cu/g dry flesh. There was no accumulation of copper in plaice muscle. Visceral accumulations after 100 days were 71, 147 and 567 μg Cu/g dry flesh for dose concentrations of 10, 30 and 100 μg Cu/1, respectively. The mean control level was 30 μg Cu/g dry flesh. The effect of copper on phytoplankton metabolism was investigated by measuring plant pigment levels and rates of primary photosynthetic fixation of C¹⁴-labelled bicarbonate. All dose concentrations reduced both the standing crop and the rate of photosynthesis per unit of chlorophyll a. The effects of copper on growth and condition of T. tenuis and P. platessa were investigated. All dose concentrations adversely affected T. tenuis condition (dry flesh weight for standard individual). The effect was most marked during deposition of winter reserves. In the absence of plaice predation, there was a decrease in the mean siphon weight for T. tenuis exposed to 30 and 100 μg Cu/1. For plaice, all dose concentrations of copper resulted in reduced growth, but there was no significant change in condition or biochemical composition. The ash weight of fish exposed to copper was significantly higher than for controls.