The Mediterranean proliferation of Caulerpa taxifolia provides an opportunity to examine the extent to which an introduced species can modify biodiversity. During 1992, benthic invertebrates were sampled in Roquebrune-Cap Martin area, at depths of 6 and 10 m, from a Caulerpa station and a reference station. Species richness is slightly lower at 6 m within Caulerpa while the number of specimens is much reduced at both depths. Similarity indices compare well between reference and Caulerpa stations.