PHENOTYPIC PLASTICITY OF PARACENTROTUS-LIVIDUS (ECHINODERMATA, ECHINOIDEA) IN A LAGOONAL ENVIRONMENT

The relative sizes of the different somatic and gonad components of th e sea urchin Paracentrotus lividus (Lamarck) were studied at 2 sites i n a coastal Mediterranean lagoon to demonstrate the phenotypic plastic ity of this species to environmental conditions. Sampling sites varied with regard to substrate type, sea urchin population density, and, in particular, food resource. Results indicate that when food resources [beds of Cymodocea nodosa (Ucria) Asherson] are not limiting, P. Livid us exhibits high repletion (relative weight of the gut and its content ), gonad and test indices. When food is limited, test and gonad indice s decline and the relative size of the feeding apparatus increases. Th ese variations may be related to changes in the allocation of energy s o as to maximise the acquisition of food. These results show that P, l ividus is capable of changing its morphology in response to available food resources and demonstrate the high degree of plasticity of this s pecies.