Cadmium exposure experiments on calanoid copepods reveal significant shortfall in water quality criteria for managing coastal marine ecosystems in West Africa

Abstract

Coastal marine waters in the Gulf of Guinea are severely affected by heavy metal pollution, particularly from small scale mining activities around major rivers feeding estuaries in the Region. However, the potential impact of these environmental stressor on the productivity of planktonic organisms remain unknown. We quantified survival, reproduction and faecal pellet production rate of calanoid copepods – Temora stylifera and Centropages velificatus, commonly found in coastal marine waters of the Gulf of Guinea – after culturing in seawater containing cadmium (proxy for toxic metals) at five concentrations (0.0, 0.05, 2, 20, 200 and 200 + µg.L^− 1) for 24 h. Increasing exposure to cadmium resulted in reduced survival and egg production, in general agreement with reports on species from other large marine ecosystems. Acute toxicity (expressed as 24-hour LC₅₀) of the metal was positively related to the size (dry weight) of the copepods, with increased severity in C. velificatus. We estimate that the maximum cadmium concentration (3–5 µg.L^− 1) currently prescribed for coastal marine waters in West Africa is higher (≥ 40%) than the concentration (0.36–1.20 µg.L^− 1) that triggers the acute toxicity of the metal. We therefore recommend a review of the water quality criteria for managing coastal marine ecosystems of the Region.