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Coral reef resilience: Balancing production and herbivory

Webster, F., Babcock, R., van Keulen, M. and Loneragan, N. (2008) Coral reef resilience: Balancing production and herbivory. In: 11th International Coral Reef Symposium, 7 - 11 July, Fort Lauderale.

Abstract

The Ningaloo Reef provides a unique opportunity to investigate different components of a coral reef ecosystem without the confounding effects of poor water quality and severe overfishing. This research examined a) how macroalgae affects coral recruitment and b) the processes which drive macroalgal abundance. These experiments were conducted in the field using a series of caged, uncaged and partially caged treatments to examine herbivory and control for caging effects. It was identified for the first time, that both the pre- and post- settlement processes of coral recruitment were severely reduced by increased macroalgal biomass. In the presence of macroalgae - for the coral Acropora millepora: larval settlement was reduced by up to 93%, post settlement survival was approximately half and those which did survive were around 80% smaller compared to corals in uncaged plots which contained little macroalgae. This demonstrates that macroalgae can inhibit coral reef recovery by reducing coral recruitment. Bottom up versus top down influences on macroalgal abundance were examined in a multifactorial study using slow release fertilizer and cages to manipulate herbivory. Nubbins of Cyphastrea microphthalma were used as a proxy for coral recruits. Nutrients had no effect on macroalgal biomass and coral calcification. Herbivores on the other hand had a strong overriding effect. The volume of macroalgae was up to 40 times greater in caged versus uncaged plots. Over a nine month period the growth of coral nubbins in cages beneath the macroalgae was reduced by approximately 50% compared to uncaged plots. Through video analysis it was identified that the most important herbivores for controlling macroalgal abundance were large parrot fish, in particular Cholurus sordidus and Scarus schlegeli. These results emphasize the importance of protecting herbivores, in particular larger scarids from overfishing to facilitate coral recruitment and promote coral reef resilience.

Publication Type: Conference Item
Murdoch Affiliation: School of Biological Sciences and Biotechnology
Conference Website: http://www.nova.edu/ncri/11icrs/
Notes: Oral presentation
URI: http://researchrepository.murdoch.edu.au/id/eprint/10862
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