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Coral that takes a nap

New Israeli study explains coral's pulsation


by Linda Gradstein, The Media Line

April 24, 2013 | 10:16 am

Heteroxenia fuscescens

Heteroxenia fuscescens

This story originally appeared on themedialine.org.

Do you find yourself dragging; craving a nap in the late afternoon? You're not alone. Soft coral beneath the waters near the southern Israeli resort city of Eilat does the same thing.

A new study by scientists from the Hebrew University in Jerusalem and the Technion, Israel's institute of technology, discovered that a soft coral called Heteroxenia, found in the reefs off Eilat, pulsates continually except for a period of one-half-hour just before sunset. The study does not answer the napping question, but the scientists do have a theory.

“During the day the coral uses the photosynthesis to generate its food, and during the night it goes through respiration like other animals,” Uri Shavit, a professor of civil and environmental engineering at the Technion in Haifa told The Media Line. “Just before sunset when the level of oxygen is very high it can take a rest without harming its metabolism.”

What the study, funded by Israel's National Science Foundation, was trying to discover was why, unlike all other species of coral, the Heteroxenia pulsates incessantly, using up valuable energy. The reason, they found, is that the level of photosynthesis, which transforms sunlight into chemical energy, is between five and eight times greater with the movement than without it.

“Corals, which are animals, are important for the ecosystem because they live in symbiosis with algae,” Maya Kremien, a graduate student at Hebrew University who worked on the study told The Media Line. “The pulsation creates the optimal conditions for the photosynthesis of the algae.”

The study appears in the current issue of Proceedings of the National Academy of Sciences in the United States (PNAS). Kremien worked on the project for four years, developing an underwater measuring device called a particle imaging velocimeter (PIV) which measures the flow of water around the coral.

“By taking hundreds of thousands of images with the PIV, we basically have velocity vector maps,” Shavit said. “We found that the coral pulsates almost 24-hours a day. It's very beautiful. You can sit and watch it for hours.”

The study comes amid concern that the coral reef in Eilat, which is one of the most diverse in the world, has been gradually degrading. Of the nine miles of Israeli coastline along the Red Sea, less than one mile has been designated as a nature preserve. The development of the city of Eilat, sewage outflow and industrial installations have all taken a toll on the coral reefs.

In a previous study, the same group of Israeli scientists found that the motion of water is needed to increase the flow of oxygen away from the corals. This time they found that the pulsation means the coral will not be filtering the same water each time. In addition, each polyp, or coral flower, pulsates at a different rate.

The research could have some practical applications as well, in engineering or medicine.

“We are not there yet but there are a lot of interesting questions that could lead to practical use,” Shavit said. “Nature is very smart through evolution and people mimic nature in other fields. We learned to fly from birds, and to swim from fish.”

They are not sure what people can learn from coral, but they are sure it will be valuable.

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