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Ancient reefs helped shape fish diversity

Reef refugia Large coral reefs have acted as survival centres for fish biodiversity during periods of climatic upheaval, explaining the extraordinary biodiversity present in the Indo-Pacific region.

The findings appear in an international study published today in the journal Science.

Researchers used sediment core data to map the changing distribution of coral reefs around the world over the past three million years, examining sea surface temperatures and compared how these correlated with fish biodiversity today.

"The main purpose of this was to examine the role that coral reef habitat has played through time in preserving biodiversity in the marine environment," says co-author and evolutionary biologist Dr Peter Cowman, formerly of the Australian National University and now Yale University.

Their data suggests that the huge network of coral reefs stretching from the northern coast of Australia up through Indonesia and the Philippines has protected and nurtured fish biodiversity through more than thirty interglacial cycles of major cooling and warming — including rising and falling sea levels — over three million years.

These stable reefs have also helped to reseed the surrounding habitats when the climate returned to more favourable conditions, Cowman says.

This was evident in the fact that the species found in these protected areas have a much older lineage than fish species outside the refugia, reflecting the fact that the protected species were more likely to survive climate upheaval while those outside were less likely. These older lineages were then able to diversify out into the stable, but fragmented habitat.

"That is something that myself and other reef researchers have been thinking about for quite some time," says Cowman. "These coral reefs have actually provided a refuge for these reef fish lineages and have sustained them and allowed them to proliferate and produce more species."

The finding underscores the significance of large coral reef networks in helping marine biodiversity survive climatic challenge.

Future threat

But Cowman says the refuges themselves are now under threat because the warmer waters that have protected them during past glacial periods may now be hastening their downfall.

"The areas that have acted as refugia in the past are actually the areas that are going to be most under threat by future climate warming," he says.

The authors claim that given this new appreciation for the role that reefs play in preserving biodiversity, management strategies should focus on protecting large areas of reef that can provide corridors of suitable habitat for fish species.

"You don't just need to manage and maintain one reef, you need to maintain a lot of reefs that are interconnected, preserving the system as a whole rather than its pieces," Cowman says.