Scientists Decipher Jellyfish’s Mighty Sting
July 28, 2017
With summer upon us, people everywhere are flocking to the beach, where they’ll find sun, sand and surf … and jellyfish. Worldwide, the numbers of these creatures is steadily growing. And since large swarms of jellyfish can be found on coastlines every year, the frequency of people being stung by them is also on the rise.
The jellyfish belongs to the phylum Cnidaria – animals that attack their prey (plankton) and defend themselves with stinging cells containing syringes that are actually poison arrows. Although they don’t have eyes, ears, or even brains, they have survived for 600 million years, with virtually no developmental changes, and are thus among the most ancient complex creatures that have not died out.
Now, a study conducted by researchers at the Technion-Israel Institute of Technology and the University of Haifa explains for the first time the unique stinging mechanism of the nomad jellyfish (Rhopilema nomadica), which reached the Mediterranean sea in the 1970s, and which is the most common jellyfish in Israel.
“The jellyfish attacks its prey or its enemy by injecting a toxic substance by means of thousands of microscopic syringes located on each of its tentacles,” says Prof. Uri Shavit of the Technion Faculty of Civil and Environmental Engineering. “The syringe is located inside the stinging cell (nematocyte) and packaged inside a spherical capsule about 10 microns in diameter. In response to chemical changes in the environment or physical contact, pressure increases inside the capsule and the needle is ejected at a tremendous acceleration of more than 50,000,000 meters per second squared – one hundred times the acceleration of a rifle bullet.”
Many researchers around the world are studying the needle’s firing mechanism, from a folded position in the capsule to its full length. The conventional explanation is that the needle is pulled out and shoots the poisonous substance following the creation of a force mechanism called osmotic potential. This force pushes the needle and liquid like a pump pushing water upwards inside a building. The pressure exerted in this process is tremendous: 150 atmospheres. For purposes of illustration, this is the pressure needed to pump water to the top of a building nearly a mile high.
But the Technion and Haifa study (recently published in the Journal of the Royal Society Interface) found that the driving force is not limited to the capsule alone. In fact, it is a powerful osmotic mechanism that develops at the needle’s moving front. This mechanism releases the needle and pulls it like a locomotive pulling railroad cars.
The study is based on measurements taken using lab-on-chip technology and the development of a mathematical model that tracks the movement of the substance within the system. The elongation mechanism of the stinging needles was deciphered by Prof. Shavit and Prof. Gilad Yossifon of the Technion Faculty of Mechanical Engineering, and Dr. Tamar Lotan of the University of Haifa’s Charney School of Marine Sciences.
The solution was provided by an experimental system developed based on a microfluidics platform in Prof. Yossifon’s lab. This system enabled researchers to route the needle and its direction. Prof. Shavit explains, “Each capsule was placed at the opening of a micro-channel that served as a bridge between a central water channel and another channel that contained oil. We found that when the needle penetrated through oil, its elongation rate decreased by three orders of magnitude, from 50 milliseconds in water to about 25 seconds in oil.”
The researchers concluded that – unlike the conventional model – the osmotic phenomenon is not limited to the capsule, but rather occurs throughout its needle elongation. “This means that the osmotic potential can be influenced along the pathway of the needle, thus reducing its ability to penetrate the skin and preventing the stinging,” says Prof. Shavit.
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