Interview with Oren Levy: Studying coral’s biological clock 2/2

© S. Bollet / Tara Expeditions Foundation

Oren Levy, Associate Professor at the Faculty of Life Sciences, and head of the Laboratory for Molecular Marine Ecology (LMME) at Bar-Ilan University in Israel, boarded the schooner in Palau during the leg organized by the Scientific Center of Monaco (CSM). Occasionally researchers aboard Tara present their work to the crew in an informal group lecture. Oren talked about the research he’s conducting at the LMME, and also at the CSM where he’s spending a sabbatical year. Focus on the mechanisms of a particular kind of clock in this 2-part interview.

We saw in the first part of this interview that what we call the biological clock, or circadian clock, is related to sensing of the environment. Your research is focused on coral spawning.

Yes, in our research we’re trying to understand how corals, from chemical sensing to light sensing, can detect changes in their environment: for example, at sunrise, sunset, and in moonlight, the wavelengths of light change, which causes the release of gametes into the water column.


Coral spawning is quite unique.

What’s unique about spawning in coral is that it’s always synchronised with the moon light. It usually occurs 3 or 5 nights after the full moon. One of the nice examples is a study done in the Caribbean. Researchers followed the same individual colony for 20 years, to know the timing of spawning. The standard deviation, from one year to another, was plus or minus 10 minutes for a period of 20 years! It’s quite amazing when you consider that from a phylogenetic point of view, corals are very primitive.


Green Stylophora SPS coral
© Kolevski.V


The spawning of corals is not just very accurate, in many places it happens at the same time.

The Great Barrier Reef hosts over 130 species of corals. Remarkably they have been found to spawn at the same time. It’s a window of one night and we are talking about a reef of 2,500 kilometres. So, our next work was to understand which genes were involved in the timing of spawning. For that, we divided our experiment into 3 phases, just before the spawning period. We placed coral N°1 under ambient conditions, so the coral could see the changes of the moon, the sunrise, sunset and ambient light. Coral N°2 was placed every night under an artificial light, at very low light levels. Coral N°3 was shaded with a black cloth every day after sunset.


What were the results of this experiment?

We then sampled the corals all the way until the spawning night and we could profile, using different technologies, which genes were highly expressed during the spawning, to try to detect specific genes. What was unique about this was that only the coral under ambient conditions spawned. The 2 others didn’t. Then we took a sample after spawning. And then we looked at the profile of the genes and we compared them to all the other samples that we took. We finally managed to identify specific genes we believe to be important during this spawning.


Pete West / Tara Expeditions Foundation


Why did you put coral N°2 under artificial lights?

In many places around the world, like where I’m working on the Red Sea for example, there’s a lot of urbanisation around coral reefs and a lot of artificial lights, or what is known as ecological light pollution. So we wanted to know if this can affect spawning time. And it did! Another thing we found related to this work: we sampled corals during full moon days and new moon days, 4 times a day. We saw that the same genes have different expression levels during full moon days compared to new moon days. Which means that the coral knows how to count the months. So if you look at the same genes, you can show higher expression or lower expression, at midday for example, between new moon and full moon days. This is probably the way that corals follow the months. And it was the same between the 2 corals in Australia and Japan.


Does the work you’ve done aboard Tara in Palau with the Scientific Centre of Monaco also relate to this research?

Yes. I’m continuing the work I’ve done at the Inter University Institute in Eilat (IUI). In Monaco, we are doing similar experiments with artificial light to modify the physiology of corals. In Israel, we put corals under ambient conditions in our marine lab and we take other corals with which we imitate the light intensity in Eilat. Both corals stayed over 5 months under similar conditions. What we saw regarding gene expression was a lot of pathways related to cancer and fertilisation. So now we have very strong evidence that artificial lights have effects on corals, not only on spawning, but also on their physiology, metabolism, etc.


Inteview by Noëlie Pansiot

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