- Coral reef ecosystems are global biodiversity hotspots that depend on the massive calcium carbonate structures mainly deposited by scleractinian (i.e., “hard”) corals. Scleractinian coral distribution is primarily limited by sea-surface temperature, light, depth, ocean pH, sea water salinity, nutrients and sediment loads. These ecosystems are currently threatened by localized stresses such as overfishing and destructive fishing practices, pollution, terrestrial nutrient and sediment run-off, but are increasing impacted by direct and indirect impacts of rising CO2 concentrations and climate change.
- Coral reefs provide a broad range of ecosystems services with high socio-economic value: tourism, fisheries (food and employment), nutrient cycling, climate regulation, protection of the shoreline and other ecosystems (e.g. mangroves), and constitute the habitat for a wide range of species.
- Rising atmospheric CO2 concentrations have already led to a slight acidification of ocean surface waters and are projected to lead to levels of acidification that will severely impede calcium carbonate accretion. Global warming associated with greenhouse gas emissions has resulted in increased sea-surface temperatures, leading to frequent coral bleaching. Acidification and the increased frequency of local and global disturbances are projected to seriously degrade coral reefs world-wide.
- If current trends continue coral reef ecosystems may undergo regime shifts from coral to sponge or algae dominated habitats. The tipping point for this phase shift is estimated to be a sea-surface temperature increase of 2°C and/or atmospheric CO2 concentrations above 480 ppm (estimated to occur by 2050).
- Shifts in dominance from corals to sponges or algae would have dramatic consequences for coral reef communities. The reduction of habitat complexity through erosion would reduce the niches for numerous species that rely on corals for shelter, food, substrate, settlement and nursery.
- In order to avoid this phase shift, urgent local and global action is necessary. Reducing local stresses, such as the reduction of terrestrial inputs of sediment, nutrients and pollutants, is paramount to promote a higher resistance to disturbance and ensure ecosystem resilience. Fisheries require the sustainable management of marine species and should aim to conserve key functional groups such as herbivores that control algae growth. Marine protected areas networks should be designed and implemented to provide refuges and serve as larval sources to replenish harvested areas outside reserves. Globally, urgent and ambitious action to reduce CO2 emissions is necessary to limit sea surface temperature increase and water acidification.
CBD Technical Series no. 50
Biodiversity Scenarios: Projections of 21st Century Change in Biodiversity and Associated Ecosystem Services, a Technical Report for the Global Biodiversity Outlook 3
Joana Figueiredo. 2010. 2010 Tropical Coral Reefs (Appendix 10) .Biodiversity Scenarios: Projections of 21st Century Change in Biodiversity and Associated Ecosystem Services, a Technical Report for the Global Biodiversity Outlook 3 : 125 -132. https://nsuworks.nova.edu/occ_facreports/50.