Sea urchin. Bio erosion

 Sea urchins act as both herbivores and bioeroders in coral reefs. They feed on not only erect macroalgae grown on various solid substrates, but also surficial and endolithic algae associated with coral skeleton (Bak, 1994, Carreiro-Silva and McClanahan, 2001). While an adequate level of urchin grazing removes competitive algae and thus provides suitable substrates for coral settlement and growth (Carpenter and Edmunds, 2006), excessive urchin grazing will result in severe bioerosion, weakening the coral framework and increasing the risk of coral damage by storms (Glynn, 1997). High densities of sea urchins can also reduce coral recruitment, coral juvenile growth rate (Davis and Vize, 2008, Sammarco, 1980), and even consume living coral tissue with the underlying skeleton (Bak and van Eys, 1975).