Sponge community

Photo: Alfonso Siciliano · CC BY-NC-ND

Petrosia ficiformis is a massive, rock-like sponge that dominates shaded cave walls and overhangs throughout the Mediterranean. Its purple-grey surface is punctuated with tiny inhalant pores and larger exhalant oscula through which it filters several hundred litres of water per day. Inside Grotta Azzurra, dense Petrosia colonies form a living mosaic alongside other cave-specialist sponges, creating three-dimensional reef structure that shelters a diversity of cryptic invertebrates and small fish.