Variation of heavy metal contents of the green alga Caulerpa Taxifolia (VAHL) C. Agardh in its area of expansion in the French Mediterranean Sea

Abstract

Concentrations in cadmium, copper, mercury, nickel, lead and zinc were determined by atomic absorption spectrophotometry in 72 samples of the green alga Caulerpa taxifolia collected in its area of expansion in the French Mediterranean Sea. The data obtained was used to carry out a statistical study on the two main parts of the thallus (pseudo‐stolons and pseudo‐leaves), in regard to the seasons, the geographical and bathymetrical localisations and the distance from sources of pollution. The highest concentrations were those of copper and zinc, followed by lead and nickel, then by cadmium and mercury to a lesser extent. The samples collected near the most heavily populated places such as Monaco and Menton harbours, showed the highest concentrations of heavy metals. It seems that pseudo‐leaves concentrate metals more than pseudo‐stolons and that the metallic charge increases with the depth. However, these results are significant only for some of the metals. The presence of heavy metals in rather large quantities in this alga may carry a toxicological risk for the fauna that feeds on it and may be a hindrance for a possible industrial exploitation. But, it is difficult to assess the degree of this risk. Thanks to its ability to concentrate metals, however, Caulerpa can be used as a biological indicator in the "in situ”; assessment of the metallic pollution of the sea.