Corals are animals! And did you know they can also be fluorescent? In other words, they can shine even in deep water. Their bright colors are a beautiful natural expression. On July 17, 2022, scientists from Israel's Tel Aviv University and Scripps Institution of Oceanography announced that they had solved the mystery of why corals glow.


The answer is simple: to attract their prey. The study was led by O Ben-Zvi of the Scripps Institution of Oceanography and Tel Aviv University. Yoav Lindemann and Gal Eyal assisted with research and guided Yossi Loya. The researchers published their peer-reviewed findings in Communications Biology (Nature) on June 2, 2022. Yes, corals glow Scientists have long known that corals can grow. They are fluorescent creatures and can even glow at significant depths. 

Because sunlight is limited in deep water, corals cannot always rely on photosynthesis for energy. For example, a mesophotic coral ecosystem at a depth of 100-500 feet (30-150 meters) lives in a low-light, blue-shifted environment.



However, the real reason why corals glow has so far eluded scientists. Earlier theories include radiation screening or even acceleration of photosynthesis (where there is plenty of sunlight in shallower water). 

Other ideas are antioxidant activity, protection against herbivores, or attraction of symbiotic algae. 2 elongated aquatic animals with eyes at one end and many small legs on a black background. But why do corals glow? Researchers at Tel Aviv University say they have the answer. Corals use fluorescence to attract prey such as plankton. 

The scientists tested their hypothesis by trying to see if plankton was attracted to the fluorescence. The scientists conducted their tests at sea and in the laboratory. As the letter says: Using lobsters as bait The researchers used mesophotic corals for their initial experiments.

These are corals that live under low light levels, between the shallow area of ​​coral reefs and the deep, completely dark zone of the ocean. They exhibit various fluorescent displays. As a food source for these experiments, the scientists used the aquatic crustacean Artemia salina, a salt solution.

It is a kind of food for corals. The researchers gave the lobsters a choice between a fluorescent target (green or orange) and a clear, colorless target. Lobsters are most attracted to colored targets. However, fish avoid colored targets, especially orange ones.


Smiling young woman with long dark hair, looking down. The new study was led by O Ben-Zvi of the Scripps Institution of Oceanography and Tel Aviv University. Image via LinkedIn. Corals and plankton in their natural environment The second part of the test actually involved plankton in the ocean. 

The results? About 130 feet (40 meters) deep in the ocean where corals live, fluorescent traps (both green and orange) attract twice as much plankton as a clear, colorless trap. Ben-Zvi said: We conducted a deep-sea experiment to investigate the possible attraction of diverse and natural plankton collections to fluorescence under the natural currents and light conditions present in deep water. 

Because the fluorescence is primarily "activated" by blue light (deep sea light), at these depths the fluorescence naturally glows and the data from the experiment is clear, and uniform in the laboratory experiment. Finally, the researchers studied predation rates of mesophotic corals collected at 145 feet (45 meters) in the Gulf of Eilat. 

They found that green-fluorescent corals showed a 25% higher predation rate than yellow-fluorescent corals. This suggests that green fluorescence in particular is useful in attracting prey. Fluorescent coral mouths and tentacles There is more evidence that corals use fluorescence to attract prey. Namely, that their mouths and tentacles are even marked with bright colors. Cheerfulness leads the victim to her. As Loya explains.

Many corals display a fluorescent color pattern that marks their mouths or tentacle tips, a fact that supports the idea that fluorescence, like bioluminescence (the production of light by a chemical reaction), acts as a mechanism to attract prey.

The study confirmed that the sparkling and colorful appearance of corals can act as a lure to attract floating plankton to land-dwelling predators such as corals, especially in locations where corals need other sources of energy in addition to or as a substitute for photosynthesis (sugar. production symbiotic algae in coral tissue using light energy).