Sunday, May 8, 2016

Reef corals at risk from climate change, acidification--can science help?

If you leave something with a hard surface in the tropical ocean long enough, coral will settle and grow-whether it’s a set of lost keys or eyeglasses or a rock.

I’ve found coral growing on glass fishing floats and pieces of marine debris—even plastic rope. It would suggest real resilience on the part of corals, but increasingly, they seem to be suffering.

(Image: On a pink background of corraline algae, two just-attached coral juveniles form circular shapes, while a white larval coral swims by. Credit: Hollie Putnam.)
But there’s a lot we don’t know about corals, and with coral reefs at risk due to climate change and ocean acidification. Hawaiian researchers are doing some of the seminal work needed to better understand some of the issues involved. We’ll look at two of those efforts here.

In an article in the Proceedings of the Royal Society B/Biological Sciences, authors found that there are certain genetic switches that change during a coral’s life.

When coral is in larval form, free-floating, it doesn’t produce a limestone skeleton. Only after it lands on a surface does the genetic switch change positions, and it starts building rock.

“Our research on reproduction in the lace coral, Pocillopora damicornis, provided the perfect opportunity to look at a natural on-off switch in coral biomineralization,” said co-lead author Hollie Putnam, of the Hawai`i Institute of Marine Biology (HIMB).

A team of researchers from University of Hawai`i, Rutgers and the University of Haifa studied that process. A press release with more images is here. 

The paper has the painful title, “Temporal and spatial expression patterns of biomineralization proteins during early development in the stony coral Pocillopora damicornis.” The authors are Tali Mass, M. Putnam, Jeana L. Drake, Ehud Zelzion, Gates, Debashish Bhattacharya and Paul G. Falkowski.

“The better we understand how corals grow, the better we understand the way they respond to ocean acidification, rising sea surface temperatures and pollution, and can therefore forecast and manage reefs communities in the future,” said Ruth Gates, director of the Hawai`i Institute of Marine Biology.
Another feature that’s important for a marine reef’s survival during climate change is its genetic diversity. A team led by HIMB researcher Kimberly Selkoe looked into the genetic diversity of reef corals by taking more than 17,000 samples from 47 Hawaiian coral species.
(Image: Coral reef with fishes in the Papahānaumokuākea Marine National Monument. Credit: James Watt, courtesy of PMNM/NOAA.)

Their work was also published in the Proceedings of the Royal Society B. A University of Hawai`i press release on the work is here. The paper is entitled “The DNA of coral reef biodiversity: predicting and protecting genetic diversity of reef assemblages.”

The authors are Selkoe, Oscar E. Gaggiotti, Eric A. Treml, Johanna L. K. Wren, Mary K. Donovan, Hawai‘i Reef Connectivity Consortium and Robert J. Toonen. They hail from HIMB, the University of California Santa Barbara, University of St. Andrews in Scotland, and the University of Melbourne in Australia.

The research team looked at reefs on 13 Hawaiian islands in both the main Hawaiian Island group and the Northwestern Hawaiian Islands. One finding: areas with higher species diversity—more different kinds of corals—also had corals with greater internal genetic diversity.

They also found that certain reefs, ones that had been bleached due to warm water temperatures, tended to have lower genetic diversity.

“This negative impact of thermal stress on genetic diversity suggests that climate change will compromise the adaptive capacity and genetic integrity of not just corals but the entire coral reef community,” Selkoe said.

There’s an assumption that more genetically diverse reefs have a stronger capacity to respond and survive threats like warming and acidification of the oceans. The research team will be looking into that, and whether the pattern of species diversity with genetic diversity is confirmed. 

“If these relationships can be confirmed and replicated elsewhere, DNA sampling may one day allow rapid assessment of species diversity and new metrics of resilience and adaptive capacity,” Selkoe said.

The authors make the point that one technique for preserving coral reefs is to establish reserves to protect the areas with the greatest species and genetic diversity.

“The results highlight inherent feedbacks between ecology and genetics, raise concern that genetic resilience of entire reef communities is compromised by factors that reduce coral cover or available habitat, including thermal stress, and provide a foundation for new strategies for monitoring and preserving biodiversity of entire reef ecosystems,” the paper says.

But there’s still a lot to know. One question is why coral species diversity is linked to genetic diversity. One suggestion is that it may have something to do with the kinds and numbers of coral-eating fish that are in the area. The researchers did find that where there are more vegetarian fish (herbivores), there are more corals—is that just because there’s more food and shelter there, or something else. 

One bit of good news for Hawai`i is that coral bleaching due to unusually high water temperatures, while a problem here, is a much worse problem on reefs closer to the equator.

“Low-latitude Pacific reefs have experienced thermal stress up to 240% higher than Hawai‘i and documented ecological effects have also been more severe, suggesting that recent declines in genetic diversity might also be more severe at lower latitudes,” the authors write.

© Jan TenBruggencate 2016

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