For coral, red means go

Compiled by BioPhotonics staff

The color that young staghorn coral fluoresce – red or green – seems to predict whether they will swim away from their reef of origin, or stay and settle, biologists have discovered.

The Acropora millepora coral that fluoresce redder are less likely to remain and develop into coral polyps than their greener peers, according to biologists at the University of Texas. These findings may help scientists monitor how corals adapt to global warming as they shift to cooler latitudes.

At left and below right: Example of fluorescence in the adult Acropora millepora coral.

The biologists crossed different color morphs of A. millepora coral, exposing the offspring larvae to a settlement cue: ground-up calcareous red algae. They found that the larvae that inherited a redder fluorescent color from their parents were less likely than the green larvae to stay and metamorphose into reef-building polyps.

At left: Fluorescent photograph of two full-sibling young corals, three days after settlement and metamorphosis. Images courtesy of Mikhail Matz and Joerg Wiedenmann, University of Texas at Austin.

Under the influence of global warming, this particular life history trait of the larvae is expected to undergo a significant amount of evolution, said Mikhail “Misha” Matz, assistant professor of biology at the university. He says researchers expect to see the long-range dispersers, or redder coral, starting to predominate as they shift to cooler latitudes.

At right: Fluorescence of Acropora millepora larvae, one of the greener full-sib families.

It is not clear whether the coral’s fluorescence and response to settlement cues, which are both under genetic control, are functionally linked in coral, or whether there’s simply a correlation. It’s possible that fluorescence is related genetically to the capacity of larvae to sense the proximity of a coral reef, and thus might have a direct correlation.

An example of color contrast between families. The top two panels depict larvae, while the bottom two panels show young polyps just after metamorphosis.

Although the researchers do not yet understand the purpose of fluorescence in coral, they believe their discovery has brought scientists a step closer to determining its function in this sea creature.

The research is reported in Proceedings of the Royal Society B, published online Jan. 26, 2011 (doi: 10.1098/rspb.2010. 2344).