IN-VITRO CONSUMPTION OF CAULERPA-TAXIFOLIA (CHLOROPHYTA) BY ACCUSTOMED AND NON-ACCUSTOMED PARACENTROTUS-LIVIDUS (ECHINOID) - SEASONAL-VARIATIONS

In vitro short time experiments (a few weeks) show that daily ingestio n by Paracentrotus lividus (Echinodermata: Echinoidea) is weak (0-81 m g DW d(-1) ind(-1)) for Caulerpa taxifolia (Chlorophyta), compared to the data recorded with an almost totally avoided brown alga, Cystoseir a compressa (24-137 mg DW d(-1) ind(-1)) and with a preferred brown al ga, Halopteris scoparin (79-397 mg DW d(-1) ind(-1)). There is no sign ificant difference between spring (when the toxic metabolite content i s at its minimum) and summer-autumn (when it is at its maximum). In co ntrast, the absorption rate of the sea urchin fed on Caulerpa taxifoli a is significantly weaker in spring than in summer-autumn. Overall, th e daily absorbed weight is negative in spring with C. taxifolia (compa red with 18 mg DW d(-1) ind(-1) with Cystoseira compressa and 25 mg DW d(-1) ind(-1) with H. scoparia). It has also been demonstrated that P . lividus becomes accustomed to Caulerpa taxifolia, at least for short time experiments: the echinoid consumes greater quantities of this al ga especially if it is fresh when it has already consumed it previousl y.