Spatial and temporal variation in cadmium body loads of four intertidal invertebrates from False Bay, South Africa

Abstract

Increasing urbanization and industrialization along the coastal areas of False Bay in South Africa can endanger coastal ecosystems because of increasing metal pollution. To obtain baseline data on contamination levels in the intertidal zone, cadmium (Cd) body loads of four invertebrate species were measured seasonally over a period of 15 months from different sites within the bay. Specimens of Tetraclita serrata (barnacle), Oxystele sinenses (periwinkle), Cymbula oculus (limpet) and Choromytilus meridionalis (mussel) were collected and analysed to determine temporal changes in Cd body burdens. Cd concentrations were also measured in water and sediments. Cd concentrations in the intertidal animals varied considerably between sampling sites and between seasons and also occasionally between species. All four species accumulated Cd in their bodies to levels several times higher than environmental concentrations. No significant difference could be shown between the Cd concentrations in the gastropod grazers and the filter-feeders. The highest mean body load of Cd (70.67 μg/g dry weight) for a single sampling occasion was measured in the sessile barnacles (T. serrata) collected at Rooi-Els. The highest mean Cd concentration (11.95 μg/g) for the bay as a whole was measured in the limpet C. oculus. Two-way analysis of variance indicated that spatial (location) rather than temporal (seasonal) factors affected Cd concentrations in the invertebrates. Cd concentrations in False Bay sometimes exceeded the norms or water quality standards.

Key words: Cd, invertebrate body burdens, marine pollution, seasonal variations.