Fears rising sea temperatures stifling coral larvae spread

Allyson Horn ABC News 29 Apr 14;

Reef researchers says rising sea temperatures are leaving large reef systems less interconnected and potentially more vulnerable.

Scientists from James Cook University have simulated high ocean temperatures to see if coral larvae still move freely in reef waters.

They found the larvae or coral babies are more likely to stay in the reef where they were spawned.

Professor Sean Connolly says it could mean changes to reef diversity.

"For systems of very highly connected reefs like the Great Barrier Reef where there's likely to be a lot of exchange of larvae, by weakening coral's ability to do that it puts greater pressure on things like evolutionary adaptation and so forth, which can have a lot of trouble coping with periods of rapid change," he said.

"For corals, because they're attached to the reef as adults, the only way they can migrate is through the dispersal of larvae and so the less dispersal there is, the more their capacity to change their geographic range to follow suitable temperature conditions, the more that capacity is going to be impaired."

Coral stays home when the heat's on
As the ocean gets warmer, baby coral are becoming more reluctant to leave home.
9 News National 28 Apr 14;

A Queensland study has found that as ocean temperatures rise more coral larvae may remain on their birth reefs rather than exploring the underwater world and finding a new system on which to settle.

This is bad news for larger reefs like the Great Barrier Reef which rely on the recruitment of larvae from other systems but good news for smaller reefs which will retain larvae that would otherwise drift elsewhere.

Study co-author James Cook University Professor Sean Connolly says this will make it more difficult for larger systems to recover after cyclones and coral bleaching because fewer larvae will disperse from other reefs.

"The loss of connectivity can make reef systems such as the Great Barrier Reef more vulnerable," Mr Connolly, from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE), said.

Although smaller reefs will have better protections by retaining their larvae, they will have fewer opportunities to change their species to adapt to climate change, he says.

Study co-author Professor Andrew Baird, also from the Coral CoE, says the research shows climate change presents both challenges and opportunities to those who manage the reef.

"The stronger link between adults and recruits means an even greater benefit if we reduce local threats such as dredging and fishing," he said.

"(However) this does not reduce the need for global action on climate change."

Increased Local Retention of Reef Coral Larvae as a Result of Ocean Warming was published in the Nature Climate Change journal.

More coral babies staying at home on future reefs
ARC Centre of Excellence in Coral Reef Studies Science Daily 29 Apr 14;

Increasing ocean temperatures due to climate change will soon see reefs retaining and nurturing more of their own coral larvae, leaving large reef systems less interconnected and potentially more vulnerable. "We found that at higher temperatures more coral larvae will tend to stay on their birth reef," says the lead author of the study.

Researchers have found that increasing ocean temperatures due to climate change will soon see reefs retaining and nurturing more of their own coral larvae, leaving large reef systems less interconnected and potentially more vulnerable.

"We found that at higher temperatures more coral larvae will tend to stay on their birth reef," says the lead author of the study published today, Dr Joana Figueiredo from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University.

"This is good news in an otherwise cloudy picture for isolated reefs, because in the future they will be able to retain more of their own larvae and recover faster from severe storms or bleaching events," she adds.

Professor Sean Connolly, also from the Coral CoE, explains that while more coral larvae will stay close to their parents, fewer will disperse longer distances, leaving reefs less connected.

"The loss of connectivity can make reef systems such as the Great Barrier Reef more vulnerable," he said.

"So interconnected reef systems that depend on the recruitment of coral larvae may take more time to recover after a disturbance, such as a cyclone, because fewer larvae will disperse from other reefs to the disturbed reef."

Professor Connolly adds that weaker connections between reefs means warm-adapted corals, such as those in the northern Great Barrier Reef, may take longer to expand their ranges to the south.

Similarly for isolated reefs, Dr Saki Harii from the University of the Ryukyus says, "While isolated reefs can retain more of their own larvae, this also leaves them with fewer possibilities to change their species composition to adjust to climate change."

Professor Andrew Baird from the Coral CoE says the implications of the research present management with both challenges and opportunities.

"Our results demonstrate that global warming will change patterns of larval connectivity among reefs. On a positive note, the stronger link between adults and recruits means an even greater benefit if we reduce local threats such as dredging and fishing methods that can damage corals," Professor Baird says.

Nevertheless, he explains, "This does not reduce the need for global action on climate change."

Increased local retention of reef coral larvae as a result of ocean warming by Joana Figueiredo, Andrew H. Baird, Saki Harii and Sean R. Connolly appears in Nature Climate Change.

Journal Reference:

Joana Figueiredo, Andrew H. Baird, Saki Harii, Sean R. Connolly. Increased local retention of reef coral larvae as a result of ocean warming. Nature Climate Change, 2014; DOI: 10.1038/nclimate2210