how long can a sea urchin live out of water
Sea urchin Population densities vary by habitat, with more dense populations in barren areas as compared to kelp stands.[36][37] Even in these barren areas, greatest densities are found in shallow water. Populations are generally found in deeper water if wave action is present.[37] Densities decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures.[37] 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.[38]