Boulders colonized by M. pyrifera were transported into three replicated experimental areas (9 m^2^ each) located in a barren ground area. Three barren ground areas (9 m^2^ each) without manipulation were selected as controls. Invertebrate abundance was recorded weekly by scientific SCUBA divers between 15/02/2007 and 11/04/2007 always choosing days with calm sea conditions. Within experimental and control units (3 x 3 m) one SCUBA diver put hazardly three times (three replicates) a counting square of 1 m side length and recorded the macrobenthic fauna present.