Abundance, composition and survivorship of juvenile corals in the southwestern Puerto Rico, la Parguera

Abstract

The distribution, abundance, species composition and survivorship of juvenile corals over natural substratum were quantified in 6 reefs along the insular shelf off La Parguera Puerto Rico from August 2003 to August 2005. Juvenile corals were measured in 6 1m2 quadrats randomly placed along four 20 m long transects in four depth intervals (n = 96 quadrats /reef). Survivorship was estimated using six quadrats of 0.25 m2 randomly placed along the same 20 m long transects in each reef. Spatial heterogeneity was estimated with the chain method along each transect line. Spatial variability of juvenile densities was determined with a nested ANOVA model I with quadrats nested within transects, transects within depths, depths within reefs and reefs within zones. A total of 882 juvenile colonies from 26 species were counted in an area of 576m2 (1.5 ± 0.11 col/m2). Juvenile densities increased from shallow habitats (lowest densities) to intermediate and deep habitats within reefs. The spatial scales that explained 85% of the total variability in juvenile distribution was found between the intermediate scales transects (meters) and depths (hundred of meters). Survivorship and recruitment were tested with a Repeated Measures ANOVA and G-test of independence. Survivorship was higher in the intermediate (50%) habitat compare to shallow and deeper habitats. The most abundant genera were Diploria, Montastraea, Porites, Siderastrea and Agaricia and were distributed across and inshore offshore gradient. Juvenile abundances and survivorship were higher at intermediate depths 2.45 (C.I: 2.06-2.92) compare to the shallow 1.31 (C.I: 1.18-1.46) col/m2 and deep intervals 1.81 (C.I: 1.65-1.99) col/m2. New recruits were observed for all the six reefs survey and Media Luna show a total of 30 new individuals among all reefs. Coral recruitment and juvenile survivorship in southwestern Puerto Rico was variable at spatial and temporal scales. This variation was explained by factors such as life history strategies, settlement orientation, the interaction with reef organisms and the possible effects of swells produced by passing hurricanes during the study period.

En este estudio se cuantificó la abundancia, composición y supervivencia de juveniles de coral sobre el sustrato natural desde agosto de 2003 hasta agosto de 2005 a lo largo de la plataforma insular en La Parguera Puerto Rico. Se utilizaron seis cuadratas de 1 m2 colocadas a lo largo de 4 transectas de 20 metros de largo, en cuatro intervalos de profundiad en seis arrefices. La supervivencia de juveniles de coral se midió en seis cuadratas de 0.25 m2. Se utilizó un modelo anidado Anova para medir la variabilidad espacial en las densidades de juveniles de coral en 5 escalas espaciales (cuadratas anidadas en transectas, transectas en profundidades, profundidades en arrecifes y arrecifes en zonas). Un total de 882 juveniles de coral pertenecientes a 26 especies de corales escleractinios fueron contados en un area de 576m2 indicando una densidad de 1.5 ± 0.11 col/m2. El 85 % de la variabilidad espacial en la densidad de juveniles de coral fue explicado por transectas y profundidades. La escala temporal se midió con un modelo repetido de Anova utilizando la variable tiempo como la medida repetida. La densidad de reclutas tiende a disminuir desde la zona arrecifal interna hacia la zona arrecifal externa. Sin embargo, los reclutas de coral mostraron mayor sobrevivencia en los afrrecifes internos e intermedios. Los generos que mostaron mayor supervivencia, entre arrecifes y zonas fueron Diploria spp, Montastraea spp, Porites spp., Siderastrea spp., Agaricia spp. Por lo tanto, para este estudio la abundancia, composicion y supervivencia de juveniles de coral fue variable en la escala temporal y espacial a lo largo de un gradiente de profundidad. Dentro de las posibles causas que puedan estar aportando a es tas variaciones son el transporte de sedimento en el plano horizontal y la inclinación del sustrato. Asi como las marejadas causadas por el paso de los huracanes Jeanny e Ivan al Sur de la Isla de Puerto Rico.