Sea Urchin

Purple sea urchins cover the rocky surfaces at Basiluzzo at densities that reflect both healthy predator populations (keeping them from overgrazing the posidonia) and the reef's overall ecological balance. In areas where fish predators have been removed by fishing, urchin barrens replace posidonia beds — but Basiluzzo's intact grouper and wrasse populations maintain the balance. They are an important structural component of the reef, their grazing keeping algal growth in check while their empty tests provide shelter for juvenile fish and invertebrates.