Effects of sedimentation on the distribution and ecology of the reef zoanthid Palythoa caribaeorum

Palythoa caribaeorum is a common zoanthid on Caribbean coral reefs. The present study determines different aspects of the ecology of this zoanthid in various coral reefs (Enrique, Media Luna, El Corral and San Cristobal) at La Parguera, southwest coast of Puerto Rico. On each reef 4 different depth zones were selected; reef crest (∼2m deep), shallow reef front (∼3m deep), deep reef front (∼6m deep), and the sand plain (∼11m deep). Three 1 x 10m (10m2) transects were surveyed in each zone to estimate densities, size-frequency distributions, percent cover and growth of Palythoa. Studies of the effects of sedimentation on the ecology of Palythoa were performed in Enrique and Media Luna. Bedload and sedimentation rates from the water column were collected using two different types of sediment traps. Percent coverage of Palythoa was highest in the crest zone and decreased with depth at both reefs. Colony densities were not significantly different among reefs or zones. Size frequency distributions were dominated by small colonies and were significantly different among reefs and zones. Positive growth was higher in smaller colonies but did not differ significantly among colony sizes. Water column sedimentation rates were significantly higher in Media Luna compared to Enrique, but depth-related patterns differed between reefs. Sedimentation rates were greatest in the shallow crest zone at Enrique, but at Media Luna were greatest in the deep sand plain zone. These patterns may be caused by the resuspension of the sediments. Bedload transport was not statistically different between Enrique and Media Luna. At both reefs the highest bedload transport occurred in the sand plain zone followed by the crest zone and the reef front. The results do not show any correlation between Palythoa percent coverage and water column sedimentation. There is an adverse relationship of Palythoa percent coverage and bedload transport. The relatively high abundances of Palythoa and high bedload transport in the reef crest may be the result of strong wave action that cleans excess sand off colony surfaces. Alternatively, bedload transport accumulates and buries Palythoa colonies in the sand plain areas.