Sea Urchin - Ecology

Ecology

Sea urchins feed mainly on algae, but can also feed on sea cucumbers and a wide range of invertebrates, such as mussels, polychaetes, sponges, brittle stars and crinoids. Population densities vary by habitat, with more dense populations being found in barren areas as compared to kelp stands. Even in these barren areas, greatest densities are also found in shallow water. Populations are also generally found in deeper water if wave action is present. Densities also decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures. The shingle urchin (Colobocentrotus atratus), which lives on exposed shorelines, is particularly resistant to wave action.

Sea urchins are some of the favorite foods of sea otters, and are also the main source of nutrition for wolf eels. Left unchecked, urchins devastate their environments, creating what biologists call an urchin barren, devoid of macroalgae and associated fauna. Sea otters have re-entered British Columbia, dramatically improving coastal ecosystem health.