Aug 18, 2019 | Updated: 08:03 AM EDT

Biologist Unlocks the Mystery Behind Bright Blue Halos Around Coral Reefs

Apr 25, 2019 09:17 AM EDT

Malolo Barrier Reef
(Photo : Maksym Kozlenko)
Malolo Barrier Reef showing bright blue halo

In 2010, on Heron Island in Australia, Elizabeth Madin started to take interest in reef halos. Ethereal rings can be seen around coral reefs when viewed from an aerial vantage point. This has been observed for decades but scientists never really understood the phenomenon.

Madin assembled a team and almost 10 years later, produced two studies about the reef halos. 

Madin works as an assistant research professor at the University of Hawaii at Manoa. Her team's work offers fresh insight as to how and why this mysterious rings would form around coral reefs.

Healthy coral reefs would have halos that can be seen from aerial views. These are the light blue rings that indicate a patch of bare sand that encircles a coral reef. This gives way to greener Meadows for seagrass or algae.

Madin calls the reef halos "Landscape of fear" in her previous research. The biologist further explains that a distinct topography is created when predators affect the distribution of plants by threatening their prey. Her previous study also notes that "no-take" marine reserves, an area where no fishing is allowed, has shaped the halos around coral reefs.

However, in their new study, Madden's team has observed that there was no difference in Halo size from inside the no-take marine reserves boundary as compared to the coral reef halos found outside the boundary of no-take marine reserves. 

Madin later concluded that the presence of reef halos could indicate the health of predator and herbivore population. This could also indicate the health of the coral reef. 

In their study, Madin and her team used cameras and infrared dive lights positioned alongside the halos at Australia's great barrier reef. In reviewing the footage the scientists have seen that this would forage for subterranean invertebrates. This would disrupt the algae at the outer region of the halos which will enlarge the said halo.

Madin points out that coral reef halos can be observed from outer space which makes the rings instrumental in monitoring the health of coral reefs with large areas.

The biologist pointed out that there is a need to monitor coral reefs, which can be done in the most cost-effective and time-efficient ways. Their study could potentially identify which ecosystems are undergoing changes because of marine reserves or even because of fisheries. Madin further explained that their research could pave the way for a technology-based solution to monitoring large-area coral reefs.

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