BIOLOGICAL CYCLES AND RECRUITMENT OF PARACENTROTUS-LIVIDUS (ECHINODERMATA, ECHINOIDEA) IN 2 CONTRASTING HABITATS

Two populations of Paracentrotus lividus (Lamarck) (Echinodermata: Ech inoidea) from the Northwestern Mediterranean were compared to ascertai n the plasticity and adaptive value of certain biological parameters. These populations were found in habitats which differed in terms of st ability of environmental parameters and food availability. A yearly re productive cycle was seen in both communities, with a spawning season at the end of spring that lasted up to several months. Recruitment dat a, inferred from abundance of post-settlement stages, indicated lack o f settlement during the study period in the unstable community, while a major recruitment in summer, with less intense episodes occurring un til autumn, was recorded in the stable community. The intensity of rec ruitment varied over an order of magnitude in the 2 consecutive years monitored. The gonadal indices were higher and the feeding indices wer e lower in the unstable community, indicating greater allocation of re sources to reproduction, at the expense of somatic growth, in response to unfavourable conditions. The graph of the feeding and gonadal indi ces with size was parallel in the unstable community, while there was a lag between the sizes at which feeding activity and gonadal biomass reached their highest values at the stable site, indicating that feedi ng activity is not so tightly determined by gonad investment needs in the stable, food-rich community.