The species of coral responsible for establishing new reefs is threatened by climate change, over-fishing and disease, say researchers. Staghorn coral, a dominant reef builder, is experiencing its first sharp population decline after 60 million years of existence, which could lead to algae-rich reefs.

Past studies found staghorn coral is one of the most prolific reef builders in the world, found in all types of reef habitat, including coldwater reefs and tropical reefs. They are an important habitat for fish, and can dissipate as much as 97% of incoming wave energy.

Researchers from the University of Queensland studied fossil records of staghorn coral and sea-level rise data, to find how the coral is being affected by climate change. The study was published in Science Advances.

The researchers used a database to study more than 33,000 coral fossil records, stretching back more than 60 million years. They found that staghorn coral was abundant throughout changing environmental conditions in the past, appearing in the Paleocene, Holocene and Miocene epochs. They suggest that as the average sea level rose throughout millions of years, the population of staghorn coral has also increased.

Staghorn's decline

The coral population first began to decline with the European colonisation of Australia, 410 years ago, the researchers say. It has since decreased in abundance due to coral bleaching and disease.

White band disease – a contagious disease which causes white marks across the coral – has killed around 95% of staghorn coral in the Caribbean. "One need only look as far as the algal-dominated reefs of the Caribbean to find a future in the absence of staghorn corals," said John Pandolfi, co-author of the study.

Staghorn coral contributes disproportionately to the systems needed to maintain reefs because of its fast growth and high abundance, which is why its decline is of concern. "These are the corals that have allowed reefs to prosper during past intervals of rapid sea level change," said Ken Johnson, researcher working on the study.

"But it seems as if staghorn corals will be compromised in providing this service in the future, even as we anticipate sea level rises over the next century." The researchers say that climate change and local stresses – including overfishing and pollution – are causing the decline in staghorn coral numbers.

"However, there is hope," said Pandolfi. "Relieving local pressures on staghorn corals – for example, by improving water quality – helps increase their resistance to thermal stress from climate change. So by managing local anthropogenic stressers such as sediment run-off, dredging and other sources of pollution, we can insure that these corals will be at their best when confronting global warming."