Grazing by the black sea urchin Diadema antillarum reduces algal cover and enhances coral recruitment. The overall goal of this project was to examine if there is a relationship between densities of D. antillarum with algal cover and abundance of juvenile corals. Population densities of the black sea urchin, juvenile coral abundances and algal cover were assessed along four 20m 2 transects at two depth intervals (0-3 and 3-8m) within each of two inner shelf coral reefs off La Parguera Natural Reserve (San Cristóbal and Enrique) in southwest, Puerto Rico using a 1m 2 quadrat (divided into 100 areas of 100cm 2 , each area encompassing 1% of the quadrat). Juvenile coral densities were counted and identified to genus or species. Algal cover and composition was measured using each 1% square of the 1m 2 quadrat. Urchin population densities were significantly higher at 0-3m at the two sites studied. Population densities were higher at Enrique at 0-3m than at San Cristobal but at 3-8m Diadema was not seen at Enrique. A total of 30 juvenile corals belonging to eight different genera were found. Juvenile coral densities were higher at 3-8m at the two reef sites studied. Algal cover and composition was mainly composed by crustose coralline algae at 0-3m at both reef sites. Macroalgal cover was low at both reefs. The results of this study suggest that densities of coral recruits at inner shelf reefs in La Parguera, Puerto Rico are driven mainly by differences in habitats (depth). KEY WORDSCoral recruitment, abundance, Diadema antillarum, densities, composition, correlation. RESUMENEl pastoreo del erizo negro, Diadema antillarum reduce la cobertura de algas y provee sustrato disponible para el reclutamiento coralino. La meta principal de nuestro trabajo era examinar si existe una relación entre las densidades de D. antillarum, la cobertura de algas y el reclutamiento de corales. La densidad poblacional del D. antillarum, la abundancia de corales juveniles y la cobertura de algas fueron evaluados a lo largo de cuatro transectos de 20m 2 , en dos intérvalos de profundidad (0-3m y 3-8m) en dos arrecifes de la zona interior de la Reserva Natural de La Parguera en el suroeste de Puerto Rico utilizando un cuadrante de 1m 2 (dividida en 100 áreas de 100cm 2 , cada área abarcando 1% del cuadrante). La densidad de corales juveniles fue contada e identificada a género o especie. La cobertura y composición de algas fue medida utilizando cada cuadro pequeño representando 1% del cuadrante de 1m 2 . La densidad poblacional de D. antillarum fue significativamente diferente en 0-3m de profundidad en ambos lugares. Dichas densidades fueron más altas en Enrique en 0-3m de profundidad. Sin embargo en 3-8m no fueron encontrados los erizos en dicho arrecife. Un total de 30 corales juveniles pertenecientes a ocho géneros diferentes fueron encontrados. La densidad de los corales juveniles fue mayor en 3-8m en ambos lugares. La cobertura y composición de algas fue dominada por algas crustosas coralinas de 0-3m en ambos arrecifes. La cobertu...
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