Changes in coral reefs and associated communities

Key drivers
Temperature
Ocean acidification
Storms and waves
What has happened

Climate change is already impacting coral reefs in the region, through coral bleaching, disease outbreaks, ocean acidification and physical damage from stronger hurricanes.

Coral beaching is the most visible, widespread, and iconic manifestation of climate change on reefs, with major events in the region in 1998, 2005, 2010 and 2015/16. The extent of bleaching and associated mortality varies by location and event. The most severe bleaching event affecting this region is widely considered to be 2005, with 80% of coral reefs being affected by bleaching and 40% of reefs dying at many locations across 22 countries.

A long-term coral reef monitoring programme, established in 1997, at Andes Reef, Grand Cayman, revealed a loss of 55.5% coral cover between 1997 and 2013, with a significant proportion of that loss attributed to the devastating 1998 coral bleaching episode. A further reduction in absolute coral cover between 2013 and 2016 of 32.3% has since been recorded. These changes can be attributed to elevated water temperatures during the summer months, resulting in regular bleaching events and subsequent disease outbreaks.  Observations of the reef system up to 2020 show a similar trend of decreasing live coral cover. 

In the Turks and Caicos, studies between 1995 and 2004 in South Caicos noted a significant decline in coral cover and increased disease. The 2014-2017 global bleaching event appears to have pushed some corals on Turks and Caicos’ reefs past their physiological limits, with some species unable to recover. 

Coral disease has already significantly altered the community composition of reefs in the region, with potential for more frequent disease outbreaks as seas warm. Ocean acidification is already acting as an additional stressor, affecting corals and crustose coralline algae by reducing calcification and growth rates in species critical for reef stability and structure. 

Increases in sea temperature have also led to declines in coral reproductive success and metabolic rates, as well as shifts in geographic ranges. In combination with more localised stresses, such as overfishing and degraded water quality, which could undermine the recent investment in protection of coral reefs.
 

CONFIDENCE LEVEL
MEDIUM

Medium evidence, high agreement

The fundamental physiological and ecological processes are generally understood but localised response depends on many internal and external factors and needs further research. There are also good local studies that document change in coral reefs for the region.

What could happen

The rapid pace of climate warming is likely to increase damage to coral reefs. Many global studies conclude that marine heatwaves will become more frequent, leading to more bleaching events. There is some limited evidence that bleaching could become an annual event in coming decades in this region, further damaging and reducing habitat for reef dependent communities.  

A rise in SST is expected to cause more frequent and severe coral bleaching events in the region, damaging and reducing habitats for reef fish. Increase in SST is also expected to directly impact on growth, reproduction, and survival of reef associated communities, including fish, causing geographical shifts in species at their thermal limits. 

Calcifying organisms, e.g., corals and shellfish, are likely to be impacted by ocean acidification, with potentially important consequences for the biodiversity and fisheries they support. Whilst impacts from ocean acidification are likely to vary by species, models agree that the coralline algae that helps bind reefs together, are likely to be negatively affected. 
 

CONFIDENCE LEVEL
MEDIUM

Medium evidence, medium agreement

For future impacts there is more uncertainty. A minority of scientists suggest that some corals could adapt to temperature rise but this remains a point of debate. The effects of ocean acidification are highly variable by species so predicting ecological outcomes is extremely difficult. However, a few key functional groups, like coralline algae seem clearly impacted across species.