Données préliminaires sur les relations entre Paracentrotus lividus, Arbacia lixula et le phytobenthos dans la baie de Port-Cros (Var, France, Méditerranée).

The dominant food items in individual pellets in the guts of Paracentrotus lividus and Arbacia lixula (Echinoidea) were identified. In individuals from rocky substrata, the coefficient of similarity for the contents of 25 pellets sub-samples was between 0.5 and 0.6 in a P. lividus and between 0.7 and 0.8 in an A. lixula. In individuals from a Posidonia oceanica seagrass meadow, the coefficient of similarity for the contents of 25 pellets sub-samples was between 0.7 and 0.8 in P. lividus. As a result, the 100 pellets sub-samples which were analyzed for each gut can be regarded as adequate to ascertain the composition of gut contents. On rocky substrata, with a relatively high density of herbivores, the species eaten (Dictyotales, Sphacelaria sp. plur.) and not eaten (Corallina elongata, Amphiroa cryptarthrodia, Gelidiales) by P. lividus and A. lixula were nearly the same, with the exception of Cystoseira sp. plur. and Posidonia oceanica leaves which were eaten by P. lividus, and crustose corallines which were eaten by A. lixula. In the Posidonia oceanica meadow, with a low density of herbivores, P. lividus consumed primarily the green and brown leaves of P. oceanica.