Abstract

The massive die-off of the key grazer Diadema antillarum is thought to be one of the main causes of the “phase-shift” from coral reefs to algal reefs in the Caribbean. More than 25 year after the die-off little is known about the current population condition in Puerto Rico. The main objectives of this study were to quantify and compare the abundances of D. antillarum during 2009 - 2010 at five sites in Puerto Rico: Escambron (ESC), Luquillo (LUQ), Vega Baja (VB), Tamarindo (TAM), and Punta Soldado(PS). At each site all sea urchins found within five 20 m2 (10 m x 2 m) belts transects, randomly established at 3 - 5 m in depth, were counted and measured. In 2009 densities varied between 12.2 ind/20 m2 in PS, and 45.6 ind/20 m2 in LUQ meanwhile in 2010, densities varied between 10.6 ind/20 m2 in LUQ, and 24.2 ind/20 m2 in VB. However, two-way ANOVA indicates that densities were not significantly influenced by site. In contrast, densities differed significantly between sampling periods probably to a significant reduction in sea urchin abundance at observed at LUQ. This event may be the causal factor behind the interaction between sites and time; at others sites densities did not differed significantly among 2009 - 2010. Furthermore, number of juveniles (< 4 cm) were relatively low varying between 2 ind/20 m2 and 14 ind/20 m2 at VB and TAM, respectively in 2009, meanwhile in 2010 were even lower varying between 0 ind/20 m2 at VB and 5 ind/20 m2 at TAM. These results indicate that abundances of D. antillarum still low compared to pre-mass mortality. Numbers of juveniles suggest that population recovery may not occur in the near future.