FSU researchers uncover how “cryptic species” react otherwise to coral bleaching – Watts Up With That?
FLORIDA STATE UNIVERSITY
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IMAGE: THE CORAL REEF IN MOOREA BEFORE BLEACHING KILL THE LARGER CORALS IN 2019. View More CREDIT: FSU COASTAL AND MARINE LABORATORY / SCOTT BURGESS
Certain brightly colored coral species on the ocean floor seem indistinguishable to many divers and snorkelers, but Florida State University researchers have found that these genetically distinct marine invertebrates differ in their response to ocean warming, which has implications for the long-term health of coral reefs .
Researchers used molecular genetics to differentiate between corals that look nearly identical and to understand which species can best cope with thermal stress. Her research was published in the journal Ecology.
‘Being able to see the differences between these coral species that cannot be identified in the field – known as’ cryptic species’ – will help us understand new ways in which coral reefs increase their resilience in the face of disturbance said Associate Professor of Biological Science Scott Burgess, the lead author of the paper.
Researchers were studying the coral ecosystem on the island of Moorea in French Polynesia when a coral bleaching event broke out in 2019.
Corals get their color from algae that live in their tissues and with which they have a symbiotic relationship. But when corals are stressed – for example by high water temperatures – algae leave the coral, which turns white, hence the term “bleaching”. Bleached corals are not dead, but they are more vulnerable and more likely to die.
Most of the corals in Moorea belong to the genus Pocillopora. During the event, researchers found that about 72 percent of coral colonies in this genus were bleached and up to 42 percent died afterwards.
At first it seemed that the largest colonies were more likely to bleach, but when the scientists examined tissue samples from the coral, they found that colonies belonging to a particular genetic lineage, not coral size, were most important in determining the fate of the coral were corals.
“Because Pocillopora species look so similar, they cannot be reliably identified in the field, which has in the past forced researchers to study them as a single group,” said Erika Johnston, postdoctoral fellow in the Department of Biological Science and a co-author of the Paper. “Molecular genetics enables us to reconstruct their evolutionary ancestors and in this case is an essential step in the identification of species.”
About 86 percent of the deceased Pocillopora corals belonged to a group that shares a number of variations of DNA known as a haplotype, which reflect their common evolutionary ancestry.
“The good news is that not all corals died from bleaching and many species survived,” Burgess said. “The bad news is that, as far as we know today, the species that died is endemic to that particular region. On the one hand we are concerned about losing an endemic species, on the other hand our results show how co-occurring cryptic species can contribute to the resilience of corals. “
This is an environmental analogy to a diverse financial portfolio, where having a variety of investments reduces the likelihood of total loss.
“Having several species that have a similar function for the reef ecosystem but differ in their response to disturbance should increase the likelihood that Pocillopora corals will continue to play their part in the system, even if the exact species may be mixed up,” said Burgess.
Maintaining healthy ecological portfolios can be a better management option than trying to restore a particular species.
“If we maintain the right kind of diversity, in a sense, nature can choose the winners and losers,” said Burgess. “However, the concern for us scientists is that ecological portfolios that can maintain coral reef resilience will be increasingly undermined under current and ongoing climate change unless government leaders and companies take action to reduce carbon emissions. This is worrying as coral reef ecosystems provide economic, health, cultural and environmental goods and services that humans rely on. “
Future research will examine the composition of the algae living in the coral, the depth distribution of each cryptic coral species, and the evolutionary relationships between the cryptic species.
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Researchers from the Hong Kong University of Science and Technology, the Scripps Institution of Oceanography, and California State University, Northridge, contributed to this study.
This work was done on a National Science Foundation grant to Burgess.
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