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Fluorescence could help diagnose sick corals

Imaging technique offers a new way to monitor reef health

By
7:00am, November 17, 2017
Montipora capitata

GET YOUR GLOW ON  The reef coral Montipora capitata naturally fluoresces in red and cyan, as seen in this confocal microscopy image.

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Sickness makes some corals lose their glow.

Disease reduces a coral’s overall fluorescence even before any sign of the infection is visible to the naked eye, a new study finds. An imaging technique that illuminates the change could help with efforts to better monitor coral health, researchers report November 6 in Scientific Reports.

Many corals naturally produce fluorescent proteins that glow in a wavelength of light that human eyes can’t see in natural light. Previous studies have shown that heat stress and wounding, among others stressors, can affect coral fluorescence, but the new study is the first to look at the relationship between fluorescence and infectious disease.

Jamie Caldwell, a disease ecologist now at Stanford University, and colleagues used a technique called live-imaging laser scanning confocal microscopy to compare fluorescence in living fragments of healthy  and diseased  Montipora capitata coral. The reef coral, common in Hawaii, fluoresces in red and cyan, and can contract a bacterial infection called Montipora white syndrome, which causes coral lesions and tissue loss.

The diseased bits looked healthy at the macroscopic level, but under the researchers’ microscope, the sick coral’s pallid complexion was pronounced. Computer analyses of the microscopy images  quantified the lost glow (red is the total area of fluorescence, black regions are where fluorescence was lost, and white lines indicate edges between the two zones). Among the samples studied, healthy coral had on average 1.2 times as much fluorescence area as diseased fragments. Diseased coral had disorganized and fragmented patterns of fluorescence — similar to a forest that has been logged extensively, the researchers found. 

Such research “is transformative in our struggle to visualize the dance between pathogen attack and host response in the initial attack,” says Drew Harvell, a disease ecologist at Cornell University.

Many coral diseases appear to be increasing around the world, even when accounting for increased research effort, Caldwell says. Along with bleaching events and pollution, disease is considered one of the major contributors to reef declines globally. The new technique could be used for other coral species and diseases, she says.

Citations

J.M. Caldwell et al. Intra-colony disease progression induces fragmentation of coral fluorescent pigments. Scientific Reports. Published online November 6, 2017. doi: 10.1038/s41598-017-15084-3.

Further Reading

T. Sumner. The Great Barrier Reef is experiencing a major coral bleaching event right now. Science News Online, April 11, 2017.

L. Hamers. Seagrasses boost ecosystem health by fighting bad bacteria. Science News. Vol. 191, March 18, 2017, p. 14.

A. McDermott. Reef rehab could help threatened corals make a comeback. Science News. Vol. 190, October 29, 2016, p. 18.

S. Schwartz. Heat may outpace corals’ ability to cope. Science News. Vol. 189, May 14, 2016, p. 10.

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