Download - ARC Centre of Excellence for Coral Reef Studies

National Benefi t Case-StudyCase Study 2Building Resilience toClimate ChangeThe coral reefs of Australia, particularlythe Great Barrier Reef, Ningaloo Reef,and Lord Howe Island World HeritageArea are Australian national icons, ofgreat economic, social, and aestheticvalue. Tourism and fisheries on theGreat Barrier Reef alone contribute$5.9 billion annually to the nation’seconomy, and provides employment for63,000 people. Globally, the welfare of500 million people is intricately linkedto the goods and services provided bycoral reef biodiversity, such as fisheriesand tourism. Uniquely among tropicaland sub-tropical nations, Australia hasextensive coral reefs, a small populationof relatively very wealthy and welleducatedcitizens, and well-developedinfrastructure. Coral reef research is onearea where Australia has the capability,indeed the obligation, to achieve worldleadership.Coral bleaching, over-fi shing anddeclining water-quality can result indestructive algal blooms and a loss ofecological resilience. One of the mostvisible signs of a decline in the conditionof coral reefs is the widely documented“phase-shift” from a healthy coraldominatedstate to a weedy macro-algaldominated state. Loss of coral followingbleaching can also lead to reductions infi shes and other reef organisms. In 2006,the ARC Centre has undertaken cuttingedgeresearch that provides new insightsinto the processes involved in undesirablephase-shifts, and how they can becontrolled and managed. This informationis of critical importance to reef managersand policy makers worldwide.Programs 2 and 5 have begun this yearto quantify successional changes inalgal and coral assemblages on reefsthat are open and closed to fi shing, andto undertake novel experiments thatmanipulate the density of herbivorousand carnivorous fi shes. Responsevariables include the demographicmechanisms of coral-macroalgalinteractions and sub-lethal changesin the physiology of corals followingcoral bleaching and algal blooms.Mathematical modelling was alsoundertaken by Sean Connolly and histeam in 2006 to understand how changesin run-off of nutrients from coastalagriculture, which promotes algal growth,affects the control of algal blooms bygrazing reef fi shes.Phase-shift can be triggered by a lossof herbivores, especially parrotfishesand surgeonfi shes. However, thecritical question remains: how can thiscoral-algal phase-shift be reversed?In one of the world’s largest herbivoreexclusion experiments, a team from theARC Centre of Excellence simulatedoverfi shing on the Great Barrier Reef,which triggered a phase-shift to macroalgaeon a previously healthy reef. Theythen fi lmed the recovery of the reef onceherbivorous fi sh were re-introduced,using remote underwater digital videoscameras. Remarkably, only two of the27 herbivorous fi sh species present inthe region had any signifi cant impact.What was most surprising was that thedominant browser was a rare batfi sh,Platax pinnatus, a species previouslythought to be an invertebrate feeder.Parrotfi shes and surgeonfi shes, whichare the routine consumers of seaweed oncoral reefs, were unable to reverse runawayalgal blooms. The results revealedthe unexpected importance of a singlerare species in the recovery of coralreefs. This fi nding was highlighted inDecember 2006 in over 50 media storiespublished worldwide.Selected 2006 ReferencesBellwood, DR, Hoey, AS, Ackerman,JL and Depczynski, M (2006). Coralbleaching, reef fi sh community phaseshifts and the resilience of coralreefs. Global Change Biology 12(9):1587-1594.Bellwood, DR, Hughes, TP and Hoey, AS(2006). Sleeping functional groupdrives coral-reef recovery. CurrentBiology 16(24): 2434-2439.Hughes, TP, Rodrigues, MJ, Bellwood,DR, Ceccarelli, D, Hoegh-Guldberg,O, McCook, L, Moltschaniwskyj,N, Pratchett, MS, Steneck, RS andWillis, B. Phase Shifts, herbivory, andthe resilience of coral reefs to climatechange. Current Biology 17(4): (InPress).Lebel, L, Anderies, JM, Campbell, B,Folke, C, Hatfi eld-Dodds, S, Hughes,TP and Wilson, J (2006). Governanceand the capacity to manage resiliencein regional social-ecological systems.Ecology and Society 11(1): 19.Wilson, SK, Graham, NAJ, Pratchett,MS, Jones, GP and Polunin, NVC(2006). Multiple disturbances and theglobal degradation of coral reefs: arereef fi shes at risk or resilient? GlobalChange Biology 12(11): 2220-2234.Hoegh-Guldberg, O (2006). Complexitiesof coral reef recovery. Science311(5757): 42-43.43