Investigating sea urchin densities critical to macroalgal control on degraded coral reefs

Dajka, J.-C. and Beasley, V. and Gendron, G. and Graham, N.A.J. (2021) Investigating sea urchin densities critical to macroalgal control on degraded coral reefs. Environmental Conservation. ISSN 0376-8929

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Summary There is an assumption that tropical sea urchins are macroalgal grazers with the ability to control macroalgal expansion on degraded coral reefs. We surveyed abundances of Echinothrix calamaris, an urchin species common in the western Indian Ocean on 21 reefs of the inner Seychelles and predicted their density using habitat predictors in a modelling approach. Urchin densities were greatest on patch reef habitat types and declined with increasing macroalgal cover. Next, we experimentally investigated the macroalgae-urchin relationship by penning two sea urchin densities on macroalgal fields. Over six weeks, the highest density treatment (4.44 urchins m-2) cleared 13% of macroalgal cover. This moderate impact leads us to conclude that controlling macroalgal expansion is not likely to be one of the main functions of E. calamaris in the inner Seychelles given the current densities we found in our surveys (mean: 0.02 urchins m-2, maximum: 0.16 urchins m-2).

Item Type:
Journal Article
Journal or Publication Title:
Environmental Conservation
Additional Information: The final, definitive version of this article has been published in the Journal, Environmental Conservation, ?, ?, pp ?-? 2021, © 2021 Cambridge University Press.
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04 Mar 2021 12:25
Last Modified:
26 May 2023 04:21