<P> Sea urchins are some of the favorite foods of sea otters and California sheephead, and are 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 . </P> <P> Sea urchins have conquered most sea habitats, on an extremely wide range of depths . Some species, such as Cidaris abyssicola, can live down to several thousands of meters deep . Many genera are totally indentured to the abyssal zone, such as many cidaroids, most of the genera in the Echinothuriidae family, or the strange genus Dermechinus . One of the deepest - living family is the Pourtalesiidae, strange bottle - shaped irregular sea urchins that live only in the hadal zone and have been collected as far as 6850 meters deep in the Java trench . Nevertheless, this makes sea urchin the class of echinoderms living the least deep, compared to sea cucumbers and crinoids that remain abundant below 8000 m . </P> <P> Sea urchins can be found in all climates, from warm seas to polar oceans (like the polar sea urchin Sterechinus neumayeri). They adapt their diet to their environment: In rich ecosystems they feed mainly on algae that allow a quick growth; in less rich bottoms they adopt a slower metabolism, adapted to a less calorific diet . </P> <P> The shingle urchin (Colobocentrotus atratus), which lives on exposed shorelines, is particularly resistant to wave action . It is one of the few sea urchin that can survive many hours out of water . </P>

Where do sea urchins live in the world