Orange encrusting sponge

Photo: Matthieu Gauvain · CC BY-NC

Crambe crambe is one of the most ecologically significant encrusting sponges in the western Mediterranean, producing cytotoxic alkaloids that deter most grazers and allow it to outcompete other sessile organisms for hard substrate. On steel wrecks it spreads in vivid orange sheets across vertical surfaces, providing settlement sites for bryozoans, tunicates, and juvenile fish. The sponge also acts as a bioindicator — dense healthy crusts on a wreck indicate clean, well-oxygenated water with low sedimentation.