Physiological and cytological biomarker studies using Perna perna for marine pollution monitoring.

Abstract

Urbanised and industrial coastal areas in South Africa are most vulnerable to the effects of marine pollution, and the Kwa-Zulu Natal coastline is particularly at risk. The mussels Perna perna, from a polluted (Isipingo Beach) and unpolluted (Park Rynie) site, and Brachidontes semistriatus were evaluated for their use as potential bioindicator organisms. The mussels were subjected to increasing copper concentration treatments to asses the following biomarker responses: cardiac activity, lysosomal membrane stability, malate dehydrogenase enzyme (MDH) activity and body condition index. Brachidontes semistriatus exhibited significant variations in biomarker responses only when exposed to higher Cu dosages, whereas P. perna from Park Rynie displayed distinct changes in heart rate, lysosomal membrane stability and MDH activity with increasing contaminant exposure. Perna perna from Isipingo Beach displayed significant biomarker variation in cardiac activity and lysosomal membrane stability, however differences in MDH activity were only evident at the highest Cu concentration of 100 mg.L-1. Both species from the different Cu treatments failed to show any significant changes in body condition indices due to the limited time of contaminant exposure. The mussel P. perna was therefore selected as a suitable biomonitoring species, and cardiac activity, lysosomal membrane stability and body condition index were chosen as reliable biomarkers for the study. Native P. perna from KZN responded to a distinct pollution gradient along the coastline by displaying significant bradycardia, reduced lysosomal membrane stability, poor condition indices and high heavy metal tissue concentrations. Durban, Isipingo and Umkomaas were singled out as the most contaminated sites along the coast, and Zinkwazi and Park Rynie as the least polluted. In addition, significant correlations between tissue and sediment metal concentrations suggest that the species is an effective heavy metal bioaccumulator of Cd, Pb, Zn, Cr and Fe. Similar spatial trends in seawater and mussel tissue concentrations in Durban Harbour were identified. Stations in the port located nearest to the freshwater inputs and stormwater drains displayed the highest metal concentrations in tissue and seawater, as well as adverse biomarker responses from transplanted P. perna. These results suggest that Durban Harbour is strongly influenced by tidal exchange and contaminated freshwater inflow entering the harbour. It was also found that reproduction imposes a considerable effect on P. perna body condition as spawning events in winter months result in pronounced body mass loss. The study concluded that P. perna is a highly effective bioindicator species, and cardiac activity, lysosomal membrane stability and body condition index can successfully be employed in marine pollution monitoring programmes.