Phosphate limitation influences the sensitivity to copper in periphytic algae

1. To assess the influence of nutrient limitation on copper toxicity, periphitic communities from an oligotrophic stream were exposed to copper for six to 12 days with and without the supply of nutrients (mainly P). 2. In contrast to the hypothesis that nutrient cycling in mature biofilms would protect them from Cu toxicity, low and high biomass biofilms did not differ in their physiological response to copper after 6 days of exposure. 3. A clear influence of P-limitation on copper toxicity was observed. Periphytic communities that were previously fertilised for 18 days were three times more tolerant than control communities indicating that P-limitation enhanced Cu toxicity and tolerance induction were probably related to the higher P-availability. In addition, a compensation of Cu toxicity after P-addition was observed in the long-term (after 12 days). 4. We conclude that periphyton from oligotrophic streams is more sensitive to copper than periphyton from fertilised streams, and that therefore a higher effect of chronic copper exposure is expected to occur in oligotrophic P-limited fluvial systems. 5. Extrapolation of our results to the area of study (Catalonia, north-east of Spain) indicates that while the levels of Cu commonly found in the zone may negatively affect the periphyton from oligotrophic streams, because of the interaction between Cu and P, they are not able to control the growth of nuisance algae which is common under high nutrient conditions.