1 Abundance of the long spine black sea urchin Diadema antillarum in Cuban coral reefs (1999-2003) (Workshop briefing, 2005) Pedro M. Alcolado 1 , Rosa del Valle 1 , Sergio González 1 , Hansel Caballero 2 and Ruber Rodríguez 3 . 1 Instituto de Oceanología, Ave. 1ª No. 18406, Playa, La Habana, Cuba. 2 Acuario Nacional de Cuba, Ave. 1ª, esq. a 60, Miramar, Playa, La Habana, Cuba. 3 Universidad de La Habana, Facultad de Biología, Calle 25, entre I y J, Vedado, La Habana, Cuba. INTRODUCTION A mass mortality of the urchin Diadema antillarum spread throughout the Wider Caribbean region in the 1980s, which drastically affected coral reefs through excessive proliferation of fleshy algae in detriment of stony corals (Lessios et al., 1984; Hughes et al, 1985). After two decades of that event Diadema populations have not recovered to levels comparable to those of the pre-mass mortality. However there have been isolated anecdotal and sampling evidences of local recovery in several places (e.g., CARICOMP and Warner, 2000). In Cuba, except for one paper (Herrera-Moreno et al., 1981), published information about its population density before the mass mortality was lacking. Since 1999 to 2003, in the framework of the AGRRA Program, the assessment of Diadema populations covered extensive areas of coral reefs in Cuba. Another small and isolated assessment was recently carried out in Havana City for comparing with unpublished densities recorded in 1997. The objective of this communication is to describe and discuss the results of that countrywide assessment. MATERIALS AND METHODS Density of Diadema antillarum was estimated by counting individuals along haphazardly laid 10 m long and 1 m wide belt transects, as described by AGRRA (2000). The study area comprised a total of 199 sites along the Havana coastline (northwestern Cuba), the Archipiélago Sabana-Camagüey (north central Cuba), María la Gorda (Ensenada de Corrientes: southwestern end of Cuba), southern and western margins of the Golfo de Batabanó (southwestern Cuba), Bahía de Cochinos (south central Cuba) and the Archipiélago Jardines de la Reina (southeastern Cuba). At the reef flat of Playa Franceses (Reparto Flores, west side of Havana City) a haphazard quadrat sampling was carried out on February 2004 (n = 40).