Researchers at the Technion and Tel Aviv University have deciphered the sophisticated movement pattern of the coral's arms

Researchers at the Technion and Tel Aviv University have discovered the surprising timing pattern of coral arm movement, which gives them significant advantages in supplying oxygen and food

Researchers at the Technion and Tel Aviv University have discovered the surprising timing pattern of coral arm movement, which gives them significant advantages in supplying oxygen and food. The research, which was published in the Proceedings of the Royal Society B, was conducted by Prof. Uri Shavit and the student Dror Malol from the Faculty of Civil and Environmental Engineering at the Technion and Prof. Roy Holtzman from the Department of Zoology at Tel Aviv University.

Corals are marine animals that exist when they are fixed to the substrate and therefore cannot wander in search of food. As such, they depend on the flow of water that is essential for the supply of food and oxygen and the removal of waste materials. The body of the coral is indeed fixed to the bottom, but its body is decorated with hunting arms that are sent into the water around it. The coral uses its limited muscular system and internal pumping system to retract its arms to catch prey or to defend itself from a predator, but it is unable to move the arms from side to side.

The Technion researchers photographed the hunting arms in their movement in the sea and in a wave device in the laboratory at the Inter-University Institute of Marine Sciences in Eilat, and discovered to their surprise that the movement of the arm is not passive, that is, it does not move only under the influence of the waves, but precedes the movement of the waves. According to Prof. Shavit, "in the experiments we measured the movement of the hunting arms and the speed of the water near them, and we were surprised to find that there is a sophisticated and non-intuitive pattern here - the hunting arms move at the same frequency as the frequency of the waves, that is, at the same rate, but they precede the wave by a quarter of the cycle time and thus create a difference phase. The result was intriguing because it was clear to us that the coral does not have a muscle system that can sustain proactive movement."

The research shows that when the water moves sideways, the elastic arm moves with it and "pulls"; And when the water flow weakens, the elastic force brings the arm back to the center before the water velocity changes its direction. Through mathematical equations, simulations and additional measurements, the researchers discovered that the phase difference and the increase in the relative movement between the arms and the water lead to an improvement of tens of percent in three important functions: increasing the amount of oxygen it absorbs at night; removal of excess oxygen during photosynthesis during the day; and increasing the amounts of food (plankton) that he hunts. Photographing the arm movements of other species showed that this mechanism is typical of all coral arms. According to Dror Malol, "In the dense and competitive environment of the reef, any mechanism that gives the coral an advantage over its neighbors may determine which of the coral species will survive. To date, many biological mechanisms have been revealed that help adapt to the complex reef environment, but the road to a full understanding of the physical mechanisms is still long."

Following the discovery, the researchers focused on the following issues: studying the mechanism that creates the phase difference, by developing a dynamic model to calculate the cyclical movement of the coral arms; Development of a method of measuring the elastic properties of the arms; And an investigation of the mechanisms that give corals advantages in the context of metabolism with water, by numerically solving the flow of water and the movement of solutes in order to calculate the entry and exit flows depending on the water speed and the phase difference. Among other things, they discovered that the phase difference characterizes all corals as well as other animals fixed to the substrate.

For an article in Proceedings of the Royal Society B

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