These rocky subtidal ecosystems are widespread globally on ocean shelves . They are distinguished from kelp forests (M1.2) by their lack of a dense macroalgal canopy. Indeed, their complex habitat structure is derived mostly from irregular rock forms, rather than biogenic features, and supports a diverse epibenthic fauna, with a range of mobile benthic animals (e.g. anemones), while truly sessile organisms tend to be small (e.g. turf algae, barnacles). Community structure depends on depth, wave action, currents and light: for example, turbulence specialists like barnacles are more prolific on shallower, higher energy reefs. Storms impact structure by shifting sand and dislodging larger organisms episodically.