ABSTRACT
Five species of echinoderms co-occur in the upper part of the seagrass bed of Lacco Ameno (Ischia Island, Italy). Assessments of population densities since March 1990 showed that the numbers of individuals of Paracentrotus lividus and Psammechinus microtuberculatus progressively increase while those of the three of other species (viz. Holothuria polii, Holothuria tubulosa, Sphaerechinus granulans) remain stable. The obtained results suggest that the species P. lividus is in the process of recolonisation of the upper part of the Lacco Ameno bed (the species was almost absent from the site in 1988 and 1989). Researchs are in progress to follow the recolonisation process and determine its possible impact on the seagrass bed.
