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Citi coral and village coral

Prof. Oren Levy researches the timing of the reproduction of corals around the world and is surprised by Dioc. However the biological clock of the corals is not adapted to the volume lights

Studying the reproductive timing of corals. The image was prepared using DALEE and should not be considered a scientific image
Studying the reproductive timing of corals. The image was prepared using DALEE and should not be considered a scientific image

"I always wanted to know how corals time their reproduction so precisely: once a year, a day or two after a full moon night," says Prof. Oren Levy from Bar-Ilan University. "In the Great Barrier Reef in Australia, which is 2,500 km long, most corals reproduce that night. How does this happen?"

A "biological clock" is involved in the timing of such processes: biochemical mechanisms that link processes in the living body to processes occurring in its environment. Prof. Levy decided to investigate the clock mechanism in corals and sea anemones.

Research by moonlight

"I discovered that the exact timing is achieved through a combination of several external factors that synchronize the biological clock," explains Prof. Levy. "The maturation of the reproductive cells, i.e. the sperm and egg cells, is related to the increase in the temperature of the sea water. In Australia they mature and are ready to breed in November, the summer season in the southern hemisphere. When the reproductive cells are mature, the lunar cycle helps synchronize the biological clock to a certain day of the month."What is the question? How do the biological clocks of corals and sea anemones, living in symbiosis with algae, function?

Corals and sea anemones do not have eyes (although other invertebrates, such as certain oysters, do). How do they know what the moon is like? Well, to distinguish the intensity of light you don't need complex structures like eyes; Light-sensitive molecules, photoreceptors, which can activate other molecules, such as proteins, are enough. Prof. Levy checked if there are proteins whose level in the coral or sea lily cells changes depending on the state of the moon, and indeed, he found proteins that are expressed more during a full moon period, compared to nights with a missing moon. These proteins are probably responsible for the precise timing of reproduction. As expected, high cloudiness at the time of the full moon can disrupt reproductive synchronization, and postpone coral reproduction for the next month.

Green watches

Prof. Levy found that another living creature is involved in the clock of the coral system: algae. Inside the bodies of corals and sea anemones live unicellular green algae, called cooperative algae or zooxanthellae. The corals and sea lilies provide these algae with a protected living environment, while the algae carry out photosynthesis and provide their hosts with sugar, i.e. food and energy. In order to test the relationship between the animal's clock and the cooperative acceleration, Prof. Levy and his group are studying an aphasia-type sea urchin (Aiptasia). One of its advantages is that it can be separated from its symbiotic algae, and grown separately. This is how the biological clock of the sea lily can be studied with and without algae.

The study showed that the clock of corals and sea anemones can set a 12- and 24-hour rhythm, and that the 12-hour rhythm is mediated by the tidal cycles. But the clock rhythm of the cooperative algae is 24 hours; And when algae live in symbiosis with coral or sea lilies, their presence masks the 12-hour clock and induces a 24-hour rhythm. How do algae do this? Is the factor involved the level of sugars produced in photosynthesis, or is the level of oxygen emitted as a byproduct of the process?

"In my opinion, the factor involved is the oxygen level," says Prof. Levy, "and we are close to proving this. Throughout the animal world there are many biological clocks related to intracellular oxygen levels. There is even a theory linking the evolution of biological clocks to the increase in the level of oxygen in the atmosphere 2.4 billion years ago. The connection between the oxygen level and biological clocks is probably very ancient."

The excess of light and the stomachache of the corals

Not surprisingly, human activity disrupts these sophisticated biological mechanisms. Artificial light harms the activity of many living creatures, and therefore it is called "light pollution at night". Prof. Levy and his group showed that light pollution damages the biological clock of the corals, disrupting both the timing of the maturation of the reproductive cells and the timing of their release, i.e. of the reproduction itself. The clock of corals and sea roses can set a rhythm of 12 and 24 hours, and that the 12-hour rhythm is mediated by the tide cycles

As part of their work, and with the help of a research grant from the National Science Foundation, the researchers are creating a map of light pollution in reefs around the world. The study encompasses reefs from Eilat and Aqaba to Okinawa, the Philippines and Australia. The Great Barrier Reef in Australia, for example, does not suffer from light pollution because it is very far from the coast; Whereas in Eilat and Aqaba, the reef is close to the shore and suffers from severe light pollution. The reef in the Gulf of Aqaba is exposed to the strongest artificial lighting found in the study: 5,000 times more than a full moon.

Prof. Oren Levy on a voyage with the research ship "Tara"

At the same time, the researchers are examining how the light pollution damages different components of the reef. The researchers sampled corals during the day, throughout the lunar cycle and throughout the year, and collected more than 256 samples from the northern coast of Eilat, where the light pollution is very strong, and from the southern coast, where the light pollution is less.

"We found a huge difference in the physiology, the levels of gene expression and the levels of bacteria in these two groups of corals, which we call the 'city corals' and the 'village corals,'" says Prof. Levy. "Many cyclical natural processes, such as reproductive and growth processes, have almost completely disappeared in the 'city corals'. Because of the strong artificial lighting, the corals are in a state of acute and continuous stress. In order to preserve the coral reefs, their unique beauty and the multitude of creatures that live in them, this factor must also be taken into account in the lighting planning of cities adjacent to the reefs, and the intensity of illumination of street lamps, places of entertainment and signs must be reduced."

Prof. Oren Levy in Madagascar

Life itself:

"My favorite pastimes," says Prof. Levy, "are walking with those closest to me, running, reading, and also taking time off from conducting research and writing and conducting an experiment alone, by myself, like a student at the beginning of his research."



One response

  1. I have the honor to look back almost 30 years as a young graduate student and remember the young and promising doctoral student in the laboratory of the late Prof. Zvi Dubinsky. It was clear even then that Prof. Levy would be an excellent and prolific researcher. Glad to read about circadian clocks and coral reefs

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