Regular sea urchins as drivers of shallow benthic marine community structure

Regular sea urchins may be the single most important consumer affecting shallow marine communities worldwide. Vast sea grass beds and kelp forests have been denuded by foraging aggregations of sea urchins resulting in loss of habitat, food, and changes to the physical environment. On coral reefs, sea urchins shift algal communities from fleshy algae, hostile to corals, to encrusting coralline algae that facilitates coral recruitment and reef resilience. Sea urchins evolved unique foraging capabilities in the Mesozoic Era, but their relatively small size, limited mobility, and modest defenses made them susceptible to large Cenozoic vertebrate predators including sea otters and large fish. Global fisheries-induced declines of predators over the past century may have contributed to sea urchin hyperabundances. This trend reversed rapidly in recent decades by the global sea urchin fishery. Fishing on predators and sea urchins altered the strength of interactions in food webs and in some places has created alternative stable states from which sea urchin population are slow or unable to recover.