Thanks to a double whammy of disease and bleaching, branched corals have given way to stumpier rivals in most of the Caribbean’s reefs (Image: L Alvarez-Filip, N Dulvy, J Gill (UEA), I M Côté and A Watkinson)

In just 40 years, the Caribbean’s spectacular branched corals have been flattened. Research reveals that the corals have been replaced by shorter rival species – and points to climate change as at least partly to blame.

Most of the reefs have lost all the intricate, tree-like corals that until the 1970s provided sanctuary for unique reef fish and other creatures, as well as protecting coastlines by sapping the energy of waves.

Coral diversity is important for both the many species that swell on reefs and for coastal protection, says Jennifer Gill of the University of East Anglia and a member of the research team.


She and her colleagues analysed data over the past 40 years from 500 surveys of 200 Caribbean reefs. They say that the flattening process took place in two main phases. Firstly, in the late 1970s, a condition called white-band disease swept through the reefs, killing 90 per cent of the most spectacular tree-like elkhorn and staghorn corals.

The second phase, in 1998, saw many of the remaining tree-like corals being wiped out during a massive bleaching event, probably driven by global warming.

Different corals – fast-growing but short-lived “weedy” species – then took over the reefs, outcompeting most of the remaining tree-like corals. The researchers found that flat reefs now cover 75 per cent of the Caribbean, compared to just 20 per cent in the 1970s.

“It’s difficult to see how to reverse any of this,” says Gill. The biggest problem, she says, is the sheer density of human habitation. Across the Indian Pacific, by contrast, where human habitation is sparse, reefs remain in almost pristine condition.

Decline warning

“The study confirms the dire ecological impacts of the widespread degradation of coral reefs globally, but particularly in the Caribbean,” says Alex Rogers, a marine biologist at the Institute of Zoology in London.

“The loss of structural complexity that reefs provide is a huge disaster for the species associated with reefs,” says Rogers. “Coral reefs are probably the most species-rich marine ecosystems and host an estimated 1 to 2 million species, including a quarter of all fish.”

He says the only answer may be immediate cuts in emissions of carbon dioxide from burning of fossil fuels, which would curb the amount of bleaching and limit acidification of oceans that results when they absorb carbon dioxide. “A lethal combination of increased occurrence and severity of bleaching, along with ocean acidification, will mean that already severely damaged reefs will undergo a catastrophic decline in the next 40 years,” warns Rogers.

A recent assessment of reef biodiversity by the International Union for the Conservation of Nature found that a third of shallow-water corals that build reefs faced extinction – with those in the Caribbean at greatest risk.

Journal reference: Proceedings of the Royal Society, B (DOI: 10.1098/rspb.2009.0339)