Williams, Stacey M.

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    Temporal and spatial distribution of early larval stages and post-larval recruitment of the long-spined sea urchin Diadema antillarum in La Parguera, Puerto Rico
    (2010-05) Williams, Stacey M.; García-Saís, Jorge R.; College of Arts and Sciences - Sciences; Yoshioka, Paul M.; Capella, Jorge; Alfaro, Monica; Aponte, Nilda; Department of Marine Sciences; Grove, Kurt
    This study describes temporal variations of early larval stages of the long-spined sea urchin, Diadema antillarum in neritic waters of La Parguera, Puerto Rico. Early larval stages were sampled by oblique plankton tows between the new and full moons at monthly intervals from April 2005 to July 2006, and September 2006. Early pluteus stages (< 5 days old) were found in 13 out of the 16 months of sampling, indicating that Diadema spawns throughout the year. Higher reproductive activity occurred during April and July 2005. Larval abundances were variable between years and successive months possibly reflecting the inconsistency of sampling aggregated or patchy distributions of larvae. Drogues released during the April spawning season from an area of high aggregations of mature adults indicated that a neritic, topographically steered flow fringing the inner shelf forereef platforms confined the early larval stages of Diadema within the insular shelf of La Parguera. Spatial and temporal trends of Diadema post-larval recruitment were examined during two recruitment studies at three reefs at La Parguera, Puerto Rico from September 2005 to September 2006, and at six reefs from February to April 2008 and from July to September 2008. Settling plates built out of astroturf were used to measure recruitment at monthly intervals. Plates were placed at various depths on individual mooring lines. During the first study a total of 277 recruits of Diadema were collected. Post-larvae were mostly collected from the shelf-edge reef, with the exception of two recruits collected at the midshelf reef during October 2005. There was a significant difference in recruitment among months at the shelf-edge site (ANOVA, F12, 38= 9.94, p<0.0001) with the highest value (1,067 ind/m2) occurring in July 2006. The spatial and temporal trend of the 2008 study was similar to the 2005-2006 recruitment study. From a total of 221 Diadema recruits, 218 were collected from the shelf-edge reefs (Old Buoy and El Hoyo) during 2008. The remaining three recruits were collected at Media Luna. Peak recruitment of Diadema (265 ind/m2), was observed during late summer at Old Buoy. Overall, the maximum recruitment rates observed at the La Parguera shelf-edge are higher than those measured in Curacao, Florida Keys and Canary Islands. Since surveys in the La Parguera region have demonstrated higher densities of Diadema at inshore reefs than at the shelfedge, the higher recruitment observed at the shelf-edge reefs suggest that recruitment is not a major determinant of the spatial distribution of the adult population in La Parguera. The relatively high recruitment rates of Diadema at the shelf-edge, is evident that upstream sources of larvae are available. Assuming that recruitment on the plates is representative of recruitment on the reefs themselves, the inverse relationship between recruitment and adult densities raises an important issue about the population dynamics (mortality) of this species. Post-settlement processes, such as predation pressure by microinvertebrates may have an influence on the distribution of Diadema settlers.