Why does coral glow? to lure their prey

Coral reefs glow because of their brilliance. A new study says they do this to lure their prey. Photo courtesy of Tel Aviv University/EurekAlert!.

Coral reefs the animals! And did you know they can also be fluorescent? In other words, they can radiateEven in deep water. Their bright colors are a beautiful natural display. On July 17, 2022, researchers at Tel Aviv University in Israel and the Scripps Institution of Oceanography said they were able to solve the mystery of why coral reefs glow. The answer is simple: lure their prey.

Or the study was led by Ben Zvi of the Scripps Institution of Oceanography and Tel Aviv University. Yoav Lindemann and Gal Eyal assisted in the research and supervised Yossi Loya. The researchers published their peer-reviewed findings in Communication biology (temper nature) on June 2, 2022.

Yes, coral glow

Scientists have long known that corals can glow. They are radioactive creatures and can glow even at great depths. Because sunlight is so limited in deep waters, corals cannot always rely on photosynthesis for energy. For example, medium-sized coral reef ecosystems, at depths of 100-500 feet (30-150 m), live in a color-changing low light environment.

However, the true cause of coral glow has eluded scientists until now. Previous theories involve examining radiation or even facilitating photosynthesis (where there is enough sunlight in shallow water). Other ideas are antioxidant activity, to protect against herbivores or to attract symbiotic algae.

Two elongated aquatic creatures with eyes at one end and many small legs on a black background.
larger view. | The researchers used a type of aquatic crustacean – brine shrimp – called Artemia salina in some of their fluoridation experiments. Image via Hans Hillewaert/Wikimedia Commons.

But why does coral glow?

Scientists at Tel Aviv University say they have the answer. Corals use fluorescence to attract prey, such as plankton. The researchers tested their hypothesis by trying to see if plankton are attracted to fluorescence. Scientists conducted their tests both in the ocean and in the laboratory. As the newspaper reported:

The evidence presented here—that plankton are actively attracted to fluorescent signals—points to the important role of fluorescence in the amplification of the adjacent reef food basin.

Use of crustaceans as bait

The researchers used medium corals in their first experiments. These are corals that live in low light, between the shallow reef area and the deep and completely dark area of ​​the ocean. They display a range of different fluorescent appearances.

As a food source for these experiments, the researchers used the aquatic crustacean Artemia salina, which is brine shrimp. They are one type of food source for coral reefs. The scientists presented crustaceans with a choice between a fluorescent target (green or orange) and a clear, uncolored target. Most of the crustaceans are attracted by the colored targets.

However, the fish tended to avoid colored targets, and orange targets in particular.

Smiling young woman with long dark hair looking down.
Or the new study was led by Ben Zvi of the Scripps Institution of Oceanography and Tel Aviv University. Image via Linkedin.

Coral reefs and plankton in their natural habitat

The second part of the test involved the actual plankton in the ocean. Results? About 130 feet (40 m) deep in the sea, where corals live, fluorescent traps (green and orange) attracted twice as many plankton as the clear, uncolored trap. Ben Zvi said:

We conducted a deep-sea experiment in order to study the possibility of attracting diverse and natural groups of plankton to the fluorescence, under the natural currents and lighting conditions found in deep water. Since fluorescence is mainly ‘activated’ by blue light (deep-sea light), at these depths fluorescence is naturally illuminated, and the data from the experiment was clear, similar to a lab experiment.

Finally, the researchers studied the predation rates of average corals collected at 145 feet (45 meters) in the Gulf of Eilat. They found that corals that exhibited green fluorescence exhibited 25% higher predation rates than corals with yellow fluorescence. This suggests that the green fluorescence, in particular, is useful for attracting prey.

Fluorescent coral mouths and tentacles

There is additional evidence that corals use fluorescence to attract prey. Namely, their mouths and claws themselves are brightly colored. Flour guides right prey to them. As Loya explained:

Many corals display a fluorescent color pattern that highlights their mouths or the tips of their tentacles, a fact that supports the idea that fluorescence, like bioluminescence (the production of light through a chemical reaction), acts as a mechanism to attract prey. The study proves that the glowing and colorful appearance of corals can act as a lure to attract floating plankton to land-dwelling predators, such as corals, especially in habitats where corals require other energy sources in addition to or as an alternative to photosynthesis (sugar). Production of symbiotic algae within coral tissues using light energy).

A spherical yellow brain-like structure with many twisting grooves, it sits on the ocean floor.
Corals can take on many different forms, like this wonderfully carved “brain coral” called Diploria labyrinthiformis. Image via Jan Dirk/Wikimedia Commons.

Other fluorescent objects

This new evidence is the strongest yet to explain why corals glow. Researchers say these characteristics may not be limited to corals alone. Ben Zvi said:

Despite the gaps in current knowledge regarding the visual perception of fluorescence signals by plankton, the current study provides empirical evidence for the role of prey in fluorescence lure in corals. We suggest that this hypothesis, which we call the ‘light trap hypothesis’, may also apply to other fluorescent organisms in the sea, and that this phenomenon may play a larger role in marine ecosystems than previously thought.

Coral reefs are at risk from warming ocean waters near the equator due to climate change. But it is interesting that some groups of coral have spread to subtropical waters in recent years. Hopefully this is a good sign that these wonderful creatures will continue to thrive in the years to come.

Conclusion: Why does coral glow? Researchers at Tel Aviv University in Israel and the Scripps Institution of Oceanography say they use fluorescent colors to attract prey like plankton, solving an ancient aquatic mystery.

Source: Coral Brilliance: Luring Prey in Deep Habitats

Via EurekAlert!

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