Young sibling polyps of staghorn coral (Acropora millepora) three days after settlement. In a National Science Foundation-supported study, researchers found that the ability to fluoresce may influence whether or not the coral settle on the reef of their origin or disperse, and go elsewhere.
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Staghorn coral (Acropora millepora) were the focus of a National Science Foundation (NSF)-supported study by Misha Matz, an assistant professor of integrative biology at the University of Texas at Austin, and colleagues, to address coral reef connectivity, genetics of physiology and life history traits, and their evolutionary modifications in response to ongoing climate change.
Results of the study found that young staghorn coral that fluoresce redder are less likely to settle and develop into coral polyps than their greener peers, a finding that may help scientists monitor how corals adapt to global warming because the less likely coral larvae are to settle, the more likely they will disperse from their reef of origin.
For the study, the researchers crossed different color morphs of staghorn coral and exposed the offspring larvae to a settlement cue--ground-up calcareous red algae. They observed that larvae inheriting redder fluorescent color from their parents were less likely to settle and metamorphose into reef-building polyps than greener larvae. How the coral respond to the settlement cue is strongly influenced by genetics, but it's not clear yet how that is linked with fluorescence.
"By simply looking at the color of a larval population, we may soon be able to say which larvae are going to be long-range dispersers and which will be short-range dispersers," says Matz. "Under global warming, we expect a lot of evolution of this particular life history trait." Matz believes the long-range dispersers may become dominant because the corals will need to shift to cooler latitudes as water temperatures continue to rise due to global warming.
While the genes that determine settlement and fluorescence are next to each other in the chromosome, scientists don't know if there is a correlation between the two or if this is completely random. It is also possible there could be a relation genetically between fluorescence and the ability of larvae to sense the proximity of a coral reef, making a more direct correlation between the two. Matz and his colleagues will be investigating these possibilities in the future.
But the question still remains: Why do corals fluorescence in such dramatic colors? Matz says, "Bright, multicolored fluorescence of reef-building corals is one of the most spectacular and least understood visual phenomena in the ocean, and we still have no idea what purpose it serves. But our discovery is a really good lead towards determining the function of fluorescence." [Research supported by NSF grant IOS 10-52461.] (Date of Image: October 2006)
Credit: Mikhail Matz, Joerg Wiedenmann