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MEPS
Marine Ecology Progress Series

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MEPS 414:65-74 (2010)  -  DOI: https://doi.org/10.3354/meps08730

Sea urchins, macroalgae and coral reef decline: a functional evaluation of an intact reef system, Ningaloo, Western Australia

C. L. Johansson1, 2,*, D. R. Bellwood1, M. Depczynski3

1Australian Research Council Centre of Excellence for Coral Reef Studies and School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
2AIMS@JCU, Australian Institute of Marine Science, School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
3Australian Institute of Marine Science, UWA Oceans Institute, Crawley, Western Australia 6009, Australia

ABSTRACT: The number of relatively untouched coral reefs worldwide is rapidly decreasing. Nevertheless, one coral reef ecosystem remains relatively intact: the largest west-continental reef ecosystem in the world, Ningaloo Reef in Western Australia. This study investigated the status of 2 potential bio-indicators for coral reef decline, macroalgae and sea urchin densities, on this reef. Surprisingly, both were abundant, with the presence of extensive macroalgal beds in the sandy lagoon and a sea urchin-dominated reef slope. The algal distribution on Ningaloo reflected marked cross-shelf variation in the composition of fish functional groups, with only the back reef and the reef slope exhibiting high grazing rates (completely scraped every 43 and 59 d, respectively). Estimated bioerosion rates by fishes ranged between 1 and 2.3 kg m–2 yr–1. Echinoids only played a significant role in bioerosion on the reef slopes owing to their high abundance in that habitat (>12 individuals m–2). Here, estimated echinoid erosion equalled that of the most abundant excavating parrotfish, Chlorurus sordidus. High echinoid and macroalgal abundances on this relatively intact reef system highlight the need for caution when using these metrics for evaluating reef ecosystem condition.


KEY WORDS: Ningaloo · Herbivory · Echinoderms · Algae · Parrotfish · Functional groups · Ecosystem function · Coral reef


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Cite this article as: Johansson CL, Bellwood DR, Depczynski M (2010) Sea urchins, macroalgae and coral reef decline: a functional evaluation of an intact reef system, Ningaloo, Western Australia. Mar Ecol Prog Ser 414:65-74. https://doi.org/10.3354/meps08730

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