Données preliminaires sur le contenu digestif de l'oursin comestible Paracentrotus lividus (Lamarck) soumis à l'influence d'effluents domestiques

Abstract

Populations of the sea-urchin Paracentrotus lividus were investigated in an area polluted by domestic wastes from the Marseilles sewarage outfall. The organic carbon content near the outlets us about 10 g C 1−1 in the water column; it corresponds to particles coming from the precipitation and flocculation process, these becoming quickly covered with bacteria. This organic matter provides food for the mussel-beds at 1 to 3 m depth. Sea urchins (mainly below 3 m depth) also feed on this organic deposit falling on Lithophyllum incrustans thallus flourishing down to 15–18 m depth. The sea-urchins ingest small pieces of the algae itself and some of the micro- and meiobenthos assemblage living there. The pellets of the sea-urchin stomach and gut may be divided into four types: (i) Very fine—non-identified—elements mixed with some diatoms and sponge-spicules. (ii) Particles with small mineral fragments—crystalline or amorphous—also associated with diatoms and sponge-spicules. (iii) Lithophyllum fragments, together with many diatoms but few spongespicules. (iv) At station 0 and seldom at station 1. Irregular bulks and entanglements—without any mucoid envelope—of paper-fibres and threads (chiefly of toilet-paper) which apparently cannot be digested before defecated in their original state. Analysis of the constituents in each type of pellet from the four stations investigated reveals that diet is determined by the substrate and the assemblage living within, and not upon the organic matter coming from the outlets. Pollutants from the outfall, at station 0, led to a sea-urchin diet that was higher by 2·1 for Hg, 2·3 for Cu, 2·7 for Pb and 1·6 times for Zn than at station 1, where the population densities were the highest for all investigated stations. This suggests that excessive concentration of some pollutants prevents the sea-urchin from wholly benefiting from the greater food supply available.