Differential impacts of echinoid grazers on coral recruitment

Publisher： University of Miami - Rosenstiel School of Marine and Atmospheric Science

ISSN： 0007-4977

Source： Bulletin of Marine Science, Vol.85, Iss.2, 2009-09, pp. : 121-132

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Abstract

It has been argued that recent phase-shifts towards algal dominance in the Caribbean could have a profoundly negative influence on the future survival of settling corals. In the lower Florida Keys, USA, we used field surveys in areas with recovering populations of the formerly abundant herbivorous black urchin Diadema antillarum (philippi, 1845) and comparatively stable populations of the urchin Echinometra lucunter (Linnaeus, 1758) to assess differences in the benthic communities associated with these two alternating urchin dominants. Two primary questions were addressed: (1) Are the effects of urchin grazing on benthic community composition differential based on urchin identity? and (2) how are these differences affecting coral recruitment and long-term success? Within the Diadema zone, urchin densities approached those of pre die-off levels and were associated with low macroalgal biomass and elevated coral cover. These findings are consistent with those of numerous prior investigations, and suggest that Diadema grazing is integral to the maintenance of low-biomass high-turnover algal turfs and prostrate coralline algal crusts that characterize healthy reef systems. Conversely, and despite orders of magnitude greater abundance, Echinometra was associated with chemically and morphologically defended macroalgal forms (i.e., Halimeda sp. and Dictyota sp.) and a benthos dominated by algal canopies with virtually no live coral cover. Overall, our results are concordant with those of other recent studies in the Caribbean and suggest that in the lower Florida Keys D. antillarum may be the strongest interactor in a diverse guild of invertebrate and vertebrate grazers.