Case study reference
| Spatial context
| Impact description (case study)
| Case study recommendations
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Obura, D. O. (2005). Resilience and climate change: lessons from coral reefs and bleaching in the Western Indian Ocean. Estuarine, Coastal and Shelf Science, 63(3), 353-372.
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Indian Ocean
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The impact of climate change through thermal stress-related coral bleaching on coral reefs of the Western Indian Ocean has been well documented and is caused by rising sea water temperatures associated with background warming trends and extreme climate events. Bleaching occurs when corals' ability to sustain zooxanthellae (algae residing in corals through a symbiotic relationship) with nutrients for photosynthesis is compromised due to environmental factors such as increases in temperatures and other conditions. This leads to the expulsion of the zooxanthellae.
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Reef management planning should embrace three concepts that relate to coral-zooxanthellae holobiont and reef vulnerability to thermal stress: 'thermal protection', where some reefs are protected from the thermal conditions that induce bleaching and/or where local physical conditions reduce bleaching and mortality levels; 'thermal resistance', where individual corals bleach to differing degrees to the same thermal stress; and 'thermal tolerance', where individual corals suffer differing levels of mortality when exposed to the same thermal stress.
'Resilience to bleaching' is a special case of ecological resilience, where recovery following large-scale bleaching mortality varies according to ecological and other processes. Thermal resistance and tolerance are genetic properties and may interact with environmental protection properties resulting in phenotypic variation in bleaching and mortality of corals. The presence or absence of human threats and varying levels of reef management may alter the influence of the above factors, particularly through their impacts on resilience, offering the opportunity for management interventions to mitigate the impacts of thermal stress and recovery on coral reefs.
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Reaser, J. K., Pomerance, R., & Thomas, P. O. (2000). Coral bleaching and global climate change: scientific findings and policy recommendations. Conservation Biology, 14(5), 1500-1511.
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Global
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In 1998, tropical sea surface temperatures were the highest on record, topping off a 50-year trend for some tropical oceans. In the same year, coral reefs around the world suffered the most extensive and severe bleaching (loss of symbiotic algae) and subsequent mortality on record. The global threat of rising temperatures compounds the effects of more localized anthropogenic factors that already place reefs at risk.
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Significant attention needs to be given to the monitoring of coral reef ecosystems, research on the projected and realized effects of global climate change, and measures to curtail greenhouse gas emissions. Even those reefs with well-enforced legal protection as marine sanctuaries, or those managed for sustainable use, are threatened by global climate change. Even under ideal conditions, significant changes in community structure will occur. There is thus a need to increase the urgency and effectiveness with which we manage the stressors that already place reefs at risk (e.g. anthropogenic).
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Arthur, R. (2000). Coral bleaching and mortality in three Indian reef regions during an El Niño southern oscillation event. Current Science, 79(12), 1723-1729.
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South Asia / India
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Bleaching events in three Indian coral reef regions were examined in relation to rising sea surface temperatures using quantitative rapid assessment methods between April and July, 1998. The Gulf of Kutch reefs showed an average of 11% bleached coral with no apparent bleaching-related mortality. In contrast, bleached coral comprised 82% of the coral cover in lagoon reefs of Lakshadweep and 89% of the coral cover in the Gulf of Mannar reefs. Bleaching-related mortality was high - 26% in Lakshadweep and 23% in Mannar.
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The coral mass mortality may have profound ecological and socio-economic implications and highlights the need for sustained monitoring for coral reef conservation in India.
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