Temporal variation of the sea urchin Diadema mexicanum population density at Bahias de Huatulco, Western Mexico

Abstract: Sea urchins of the genus Diadema play an important role as controlers of algal growth in coral reef and rocky reef communities, but high densities cause bioerosion of the reef framework. Between January 2006 and February 2007 (except April, July and August), population densities and mean test diameter of Diadema mexicanum were determined at Isla Montosa, La Entrega, Isla Cacaluta and San Agustín, Bahías de Huatulco, Mexico. Mean density of the sea urchins was relatively constant through time at all localities: lowest at San Agustín (0.26±0.13 ind.m-2) and highest at La Entrega (4.17±1.4 ind.m-2). There were significant differences between La Entrega and other localities. Mean test diameter ranged between 4.41±0.88 cm (Isla Cacaluta) and 4.72±0.27 (San Agustin), and did no vary significantly between localities, but there were monthly variations. Test diameter agrees with other studies. The calculated amount of CaCO3 removed by D. mexicanum showed variations between localities. The lowest rate of bioerosion occurred at San Agustín (0. 25 kg.m-2.yr-1), and the highest at La Entrega (4 kg.m-2.yr-1). The recent urchin population decrease means a reduction in their remova