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Sediments and herbivory as sensitive indicators of coral reef degradation

Christopher H. R. Goatley, College of Marine and Environmental Sciences, James Cook University; Australian Research Council Centre of Excellence for Coral Reef Studies
Roberta M. Bonaldo, College of Marine and Environmental Sciences, James Cook University; Australian Research Council Centre of Excellence for Coral Reef Studies; Departamento de Ecologia Instituto de Biociências, Universidade de São Paulo
Rebecca J. Fox, College of Marine and Environmental Sciences, James Cook University; Australian Research Council Centre of Excellence for Coral Reef Studies; Division of Evolution, Ecology and Genetics, Australian National University; School of Life Sciences, University of Technology Sydney
David R. Bellwood, College of Marine and Environmental Sciences, James Cook University; Australian Research Council Centre of Excellence for Coral Reef Studies

DOI: http://dx.doi.org/10.5751/ES-08334-210129

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Abstract

Around the world, the decreasing health of coral reef ecosystems has highlighted the need to better understand the processes of reef degradation. The development of more sensitive tools, which complement traditional methods of monitoring coral reefs, may reveal earlier signs of degradation and provide an opportunity for pre-emptive responses. We identify new, sensitive metrics of ecosystem processes and benthic composition that allow us to quantify subtle, yet destabilizing, changes in the ecosystem state of an inshore coral reef on the Great Barrier Reef. Following severe climatic disturbances over the period 2011-2012, the herbivorous reef fish community of the reef did not change in terms of biomass or functional groups present. However, fish-based ecosystem processes showed marked changes, with grazing by herbivorous fishes declining by over 90%. On the benthos, algal turf lengths in the epilithic algal matrix increased more than 50% while benthic sediment loads increased 37-fold. The profound changes in processes, despite no visible change in ecosystem state, i.e., no shift to macroalgal dominance, suggest that although the reef has not undergone a visible regime-shift, the ecosystem is highly unstable, and may sit on an ecological knife-edge. Sensitive, process-based metrics of ecosystem state, such as grazing or browsing rates thus appear to be effective in detecting subtle signs of degradation and may be critical in identifying ecosystems at risk for the future.

Key words

disturbances; ecosystem state; herbivory; management; monitoring; processes; resilience; sediment; thresholds

Copyright © 2016 by the author(s). Published here under license by The Resilience Alliance. This article  is under a Creative Commons Attribution-NonCommercial 4.0 International License.  You may share and adapt the work for noncommercial purposes provided the original author and source are credited, you indicate whether any changes were made, and you include a link to the license.

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