Coral Reefs Have 'Halos,' and They Can Be Seen from the Heavens

Halos of light-colored sand surround reef in the Red Sea.

Credit: Copyright CNES/Airbus, DigitalGlobe

What’s the story behind mystical “halos” of bare sand that surround reef?

When reefs are healthy an uncommon phenomenon happens: a border of bare sand types around the corals. These so-called halos, or brilliant circles of sand that are lacking greenery show up to satellites miles above Earth.

However previously, researchers didn’t totally comprehend precisely how they formed, and why some were larger than others. Now, 2 brand-new research studies might assist respond to the secret of how halos take shape and what conditions make them grow. [In Photos: Diving in a Twilight Coral Reef]

Halos take place when fish and invertebrate residents consume algae and seagrass growing near the reef. In time, all greenery in this zone is eliminated; these empty stretches of sand can determine from numerous square feet to numerous countless square feet, and develop a footprint around the reef that shows up from area.

Scientists in the 2 research studies just recently took a better take a look at these halos. Not just did they observe reef animal activity that suddenly extended the borders of the halos, the scientists likewise figured out that the halos might be utilized as barometers for reef health. Knowing how to translate halos from satellite images might assist researchers keep an eye on hard-to-access reefs, the research study authors reported.

In one research study, released online today (April 24) in the journal Frontiers in Ecology and Development, the researchers discovered complex types interactions formed halos in Australia’s Great Barrier Reef.

Remote undersea camera traps exposed that herbivorous fish weren’t the only reef occupants increasing the size of halos– fish that hunted burrowing invertebrates played a part also. By digging in the sand for their victim, these meat-eating fish pushed sand-dwelling algae further away from the reef and broadened the halos’ borders, the scientists reported.

More hints about the halos emerged when the researchers analyzed high-resolution satellite pictures of reef, releasing their findings today (April 24) in the journal Procedures of the Royal Society B They examined 1,372 reefs throughout the Terrific Barrier Reef, determining functions in 214 reefs; each of these included hundreds to countless little, separated coral platforms that can being surrounded by a halo.

The research study authors likewise performed undersea studies with electronic camera traps at 22 halo places, for 3 weeks.

The researchers were then able to straight compare halo patterns in waters where fishing was allowed– which would for that reason have less predatory fish– and in waters that were safeguarded, where predators would abound.

Researchers investigated coral reef halos in waters near Heron Island, in the southern part of the Great Barrier Reef.

Scientists examined reef halos in waters near Heron Island, in the southern part of the Great Barrier Reef.

Credit: Copyright DigitalGlobe

The research study authors thought that in predator-rich secured waters, herbivorous fish would be more careful and would graze near the reef; the halos would for that reason be smaller sized. In reefs that were open to fishing and had less predators, the researchers anticipated that grazing fish would be bolder, which halos would reach further from the reef, or would even be thick and vanish. However halos in both secured and unguarded waters ended up being practically the very same size, the research study authors reported.

Nevertheless, they found that halos were most likely to form in secured marine locations, “specifically the older secured locations where predator populations have actually had longer to recuperate from previous fishing,” lead research study author Elizabeth Madin, an assistant research study teacher with the Hawaii Institute of Marine Biology at the University of Hawaii at Manoa, informed Live Science.

That showed to the scientists that halos might be a reputable sign of stability in a reef’s predator-prey populations, “which is a sign of a healthy reef environment,” Madin stated.

Their findings provide brand-new proof demonstrating how laws forbiding fishing near reef neighborhoods can enhance reef health, according to the research study.

Reef are generally kept track of by scuba divers that count types and examine the condition of corals and other life. Nevertheless due to the fact that halos show up from area, satellite images might match those studies by supplying photos of how reef halos alter in time, Madin described.

They likewise use a glance at reefs that are unattainable to scuba divers, she included.

” We can take a look at them practically anywhere from satellite images, so this will offer us a much wider view than what we might ever want to finish with the conventional tracking techniques. It would match and scale what we can see,” Madin stated.

Initially released on Live Science