Major Threats to Coral Reefs Coral Reef FOODWEB • Over-Harvesting (Top-Down Effects)
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Science for Managing the Great Changing Paradigms in Marine Science Barrier Reef Scaling-up of ecology – becoming more relevant for management Terry Hughes Fisheries science is becoming more ecological (EBM) Barriers between ecology, fisheries, and social science are breaking down – e.g. No Take Areas ARC Centre of Excellence RESILIENCE Talk Outline • The capacity of a system to absorb insults or disturbances without fundamentally changing • Global threats to coral reefs into an different configuration or “state” • Resilience and phase-shifts of reefs • The system can be ecological, socio-economic or • No-Take Areas: Tools for managing both (a linked social-ecological system) ecological resilience • Alternate states may be desirable or undesirable, • A resilience approach to reef management and so management may seek to bolster or undermine resilience Major threats to Coral Reefs Coral reef FOODWEB • Over-harvesting (top-down effects) • Declining water quality (bottom- up effects) • Climate change Phase-shifts on coral reefs Coral reefs Multiple Drivers, multiple States Phase-shifts on coral reefs Basins of Attraction in Stability Landscapes Jamaica 1979 Deeper basin = higher resilience Acropora palmata zone “Elkhorn coral” Acropora cervicornis zone “Staghorn coral” Jamaica – Phase-shift to macroalgae Jamaica 1980 J.D. Woodley …but are gloom-and-doom stories from So, what is the “health” of the GBR? overseas developing countries relevant • The Great Barrier Reef is not pristine for Australian reefs? • Increased runoff since 1850 •Overseas evidence is flawed or doesn’t apply • Wild stocks of many species have been substantially reduced: • Crocodiles •Our fisheries are the best managed in • Dugongs the world • Pearl Oysters •Threats to reefs are exaggerated • Sea Cucumbers • Sharks • Turtles •Our reefs are pristine • Reef Fishes Historical evidence of Average number of sharks caught huge dugong herds annually per net (1962-1988) s "The writer's boat was once anchored in Hervey's k r a h s t Bay… For between three and four hours there f e o n r was a continuous stream of dugongs passing… r e e b p t liken to the rush of cattle out of a stock-yard after m h u g n a general muster." u e a c g a r Source: Thorne, 1876 e v A 0 8 - 9 7 Year Source: Paterson 1990 FISHING PRESSURE Coral Trout Starfish outbreaks 25 20 t h 15 g i e W 10 5 0 No-Take Fished Gary Russ (2002) Climate-change Impacts: Coral Great Barrier Reef Bleaching Accumulating damage 1960-2003 Bellwood, Hughes, Folke & Nystrom, Nature 2004 Coral cover on the GBR: 1960’s - Present Coral cover on the GBR: 1986 - Present A Percent of reefs with 60 1960-1980 s f >10% coral cover e 50 e R 40 f 0.8 o t 30 n e c 20 r e P 10 s f 0 e 0-10 11-20 21-30 31-40 41-50 51-60 >60 e 0.6 r f o t 60 n B e s f After 2000 c e 50 r e e 0.4 R 40 f P o t 30 n e c 20 r e P 10 0 0.2 0-10 11-20 21-30 31-40 41-50 51-60 >60 1985 1990 1995 2000 2005 Coral cover (%) year AIMS monitoring data Resilience eroded by loss of top predators, crown-of-thorns starfish, Summary of GBR: bleaching……a weedier fauna Megafauna rapidly declining, reefs moderately fished, coral resilience challenged by chronic crown-of-thorns outbreaks and climate change. High redundancy within functional groups: High connectivity Managing Resilience of Coral Reefs Large-scale fish exclusion experiment by incorporating the role of human activities (starting after 1998 bleaching) What are the consequences of loss of Three Treatments: large fishes from coral reefs? Full cages, partial cages, open plots In particular, does overfishing of herbivores reduce reef resilience to climate change? Sargassum heaven ……after 15 days Inside fenced plots February 2003 Coral Resilience - Recruitment Coral Recruitment 150 No. of 100 Recruits per plot 50 0 Full Cage Partial Cage Plot Treatment A Resilience approach to Management Loss of fish biodiversity is important! A new framework for Adaptive Governance • Excluding herbivorous fishes • Changing focus from reactive to proactive increases macroalgae, reduces management, based on maintaining resilience, coral recruitment, impairs anticipating future uncertainty resilience • Building an understanding of resource and ecosystem dynamics - developing new metrics to monitor resilience • Managing fisheries (and also water- quality) can prevent phase-shifts, • Developing management practices that respond to ecological feedbacks help to maintain reef resilience to future climate change. • Supporting an adaptive governance framework with (Local, proactive management in shared responsibilities, operating at multiple scale. response to a global threat) Hughes et al., TREE 2005 ACKNOWLEDGEMENTS The Resilience Alliance Packard Foundation Australian Research Council.