SciTech

New imaging technique helps diagnose sick corals

The *Montipora capitata* is a reef coral that is found in parts of the tropical Pacific Ocean and displayws red and cyan flourescence.  (credit: Courtesy of NPS Photo - Larry Basch via Wikimedia Commons) The *Montipora capitata* is a reef coral that is found in parts of the tropical Pacific Ocean and displayws red and cyan flourescence. (credit: Courtesy of NPS Photo - Larry Basch via Wikimedia Commons)

On Nov. 6, Jamie M. Caldwell, a disease ecologist at Stanford University, and her colleagues published a paper titled “Intra-colony disease progression induces fragmentation of coral fluorescent pigments” in Scientific Reports. The paper describes a relatively new technique called live-imaging laser scanning confocal microscopy and its applications in better understanding the health of corals.

Coral fluorescence — the ability of corals to glow in shades of red, blue or green under some light wavelengths, is a common yet poorly understood phenomenon.
Corals contain fluorescent proteins that possibly allow it to perform photosynthesis better by using light that would otherwise be unusable. This phenomenon helps absorb the sun’s ultraviolet rays and reflect it back to the symbiotic organisms so the they can photosynthesize under insufficient sunlight. Some scientists also suggest that this fluorescent helps protect the coral ecosystem from the harsh rays of the sun.

The researchers along with Caldwell, say that coral fluorescence is a “potentially powerful non-invasive intrinsic marker of coral disease”. Previous research suggests that stressors such as heat and wounding affects coral fluorescent pigments, but this study is the first to suggest a relationship between coral infectious disease and fluorescent pigments. The research studied the difference between fluorescent pigment distribution in healthy and diseased living samples of Montipora capitata coral — commonly known as rice coral or pore coral. it is a type of reef coral typically found in Hawaii. The diseased sample in this case was artificially created, by infecting it with the Montipora white syndrome — bacterial infection that causes tissue loss.

While comparing, the scientists found that the two coral samples looked similar on a macroscopic level. However, after observing closely, they found that the sick sample had lost fluorescence and the distribution of the fluorescent pigments was a lot more scattered and disorganized. In fact, according to an article on Science News, the healthy coral had 1.2 times more florescence area as compared to the diseased coral.

Drew Harwell, a disease ecologist at Cornell University says in the article that research in this field, “is transormative in our struggle to visualize the dance between pathogen attack and host response in the initial attack.“

This type of coral is very dependent on the organisms called zooxanthellae that live inside it. The temperature of the sea chases out these organisms, leaving the coral colorless and susceptible to disease. Corals die very quickly after that. As habitat destruction and global warming wipes out reef corals at an alarming rate, research like this is a step forward in organizing better conservation efforts.