Caribbean corals struggling to produce enough calcium carbonate to survice
By Summit Voice
SUMMIT COUNTY — Many coral reefs in the Caribbean are struggling to keep pace with erosion, as their ability to produce and accumulate calcium carbonate declines in the face of human-caused impacts, researchers from the University of Exeter reported this week. That inability to grow raises serious questions about whether the reefs will be able to adapt to rising sea levels, the researchers reported.
Coral reefs are important ocean biodiversity hotspots and serve as nurseries for a profusion of marine life. In a sweeping decision several weeks ago, federal biologists said at least 66 species of coral in the Caribbean and Pacific are in danger of going extinct because of threats linked to global warming caused by greenhouse gas emissions.
Coral cover on reefs in the Caribbean has declined by an average of 80 percent since the 1970s, driven mainly by human disturbance, disease and rising sea temperatures, and are only expected to intensify as a result of future climate change.
“Our estimates of current rates of reef growth in the Caribbean are extremely alarming,” said Professor Chris Perry, of the University of Exeter, who led the international research, team. “Our study goes beyond only examining how much coral there is, to also look at the delicate balance of biological factors which determine whether coral reefs will continue to grow or will erode. Our findings clearly show that recent ecological declines are now suppressing the growth potential of reefs in the region, and that this will have major implications for their ability to respond positively to future sea level rises,” Perry said.
Coral reefs build their structures by both producing and accumulating calcium carbonate, which is essential for the maintenance and continued vertical growth capacity of reefs. An international research team has discovered that the amount of new carbonate being added by Caribbean coral reefs is now significantly below rates measured over recent geological timescales, and in some habitats is as much as 70 percent lower.
The worldwide decline of reef ecosystems has been well documented, but the paper, published on DATE TBC in Nature Communications, is the first evidence that these ecological changes are now also impacting on the growth potential of reefs themselves.
“It is most concerning that many coral reefs across the Caribbean have seemingly lost their capacity to produce enough carbonate to continue growing vertically, whilst others are already at a threshold where they may start to erode,” Perry said.
So far, there’s little evidence of large-scale reef erosion, but the trend of decreased carbonate production makes significant erosion look much more likely. The scientists advocated for urgent action to improve management of reef habitats and to limit global temperature increases is likely to be critical to reduce further deterioration of reef habitat.
The highest rate of decline was found in in shallow water habitats, where many fast growing branching coral species have already been lost. The study compared modern-day rates with those measured in the region over approximately the last 7,000 years. In key habitats around the Caribbean, the findings suggested that in waters of around five metres in depth, reef growth rates are now reduced by 60-70 percentcompared to the regional averages taken from historical records. In waters of around 10 metres in depth, the rates are reduced by 25 percent.
The study also suggests that these key habitats must have a minimum of around 10 percent living coral cover to maintain their current structures. The amount of cover varies between sites, but some are already below this threshold and are therefore at risk of starting to erode.
The team was funded by the Leverhulme Trust (UK), through an International Network Grant. It included scientists from James Cook University and The University of Queensland in Australia, from The University of Auckland in New Zealand, Memorial University in Canada, and the University of Maine in the USA. They examined rates of carbonate production across 19 reefs in the four Caribbean countries of the Bahamas, Belize, Bonaire and Grand Cayman.