Phenotypic plasticity of Paracentrotus lividus (Echinodermata:Echinoidea) in a lagoonal environment

Abstract

The relative sizes of the different somatic and gonad components of the sea urchin Paracentrotus liv~dus (Lamarck) were studied a t 2 sites in a coastal Mediterranean lagoon to demonstrate the phenotypic plasticity 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. lividus exhibits high repletion (relative weight of the gut and its content), gonad and test indices. When food is limited, test and gonad indices decline and the relative size of the feeding apparatus increases. These variations may be l-elated to changes in the allocation of energy so as to maximise the acquisition of food. These results show that P. lividus is capable of changing its morphology in response to available food resources and demonstrate the high degree of plasticity of this species.