Olmeda Saldaña, Manuel F.

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    Experimental evaluation of direct and indirect effects of Diadema antillarum on benthic community assemblages and coral recruitment in La Parguera, Puerto Rico
    (2020-05-27) Olmeda Saldaña, Manuel F.; Cruz Motta, Juan J.; College of Arts and Sciences - Sciences; Weil, Ernesto F.; Williams, Stacey M.; Department of Marine Sciences; Rodríguez Abudo, Sylvia
    Once described as a noxious species, the long-spined sea urchin Diadema antillarum is now considered an ecologically important species for coral reef health and many efforts have been focused towards their recovery after an unknown waterborne pathogen caused a mass die-off throughout the Caribbean. D. antillarum is considered a keystone herbivore that controls algal cover on coral reefs, as drastic reductions of the species have been associated to significant increases of algal cover. However, most of the evidence that sustain this model comes from observational studies where processes (explanations) have been proposed from descriptions of temporal and spatial patterns (relationships). Within this context, a manipulative experiment was conducted to test the effects of D. antillarum densities and rugosity on benthic assemblages and coral recruitment on coral reefs in La Parguera, Puerto Rico. The field experiment consisted of fencing 1 m2 plots (metal fence corrals) of high (coral heads) and low (coral rubble and/or small coral heads with low structural heterogeneity) rugosity. In each treatment, there were different densities (0, 1, 5 and 10 ind./m2) of D. antillarum enclosed per plot. Inside these experimental plots, 10 cm2 photo-quadrats (3 permanent and 3 random) were taken during eight sampling times (six months) to estimate the temporal change in benthic cover and coral recruitment. Multivariate and univariate analyses indicated the following: 1) presence of D. antillarum significantly decreased the cover of turf algae by 86%, Dictyota spp. by 25% and increased clean substrate by 72% at both sites, but did not increase coral recruitment; 2) rugosity is an important factor when considering the effects of herbivory by D. antillarum; 3) densities of 1 D. antillarum/m2 is not enough to control algal cover; 4) a minimum of 5 D. antillarum/m2 are required to restore low and high rugosity reefs. Based on the results, it is proposed that reintroduction of D. antillarum can be used as a restoration tool, as it can effectively decrease algal cover and create clean substrate which could potentially enhance coral recruitment.