A lionfish photographed by Shulamit Koretz, a diving instructor from Shulamit’s Eilat Diving Adventures, on a scuba dive with the author
The Red Sea is one of the oldest known bodies of water in the world. It is also one of the richest in biological diversity and abundance of life. Each year many tourists from around Israel and abroad come to Eilat to experience the wealth of underwater life in the Red Sea. For those who prefer to stay dry, there are glass-bottomed boats and the underwater observatory. However, for a fully immersive experience, the snorkeling and scuba diving are unlike anywhere else in the world.
The best diving in the area can be found by heading slightly south from Eilat toward the Egyptian border, to the Coral Beach Nature Reserve. The reserve was established by the Nature and Parks Authority of Israel which governs the preservation of the sensitive coral reef environment by controlling the number of guests allowed into the reserve.
It is difficult to describe or to imagine just what it feels like to dive around a coral reef. The feeling of weightlessness with more than 20 meters of water overhead gives the sensation of flight. Even though water is a part of everyday life, it takes an experience like diving to realize just how different life can be under the sea.
Tourists are not the only people attracted by the wonders of the coral and wildlife; there is also a world-class research facility in the nature reserve. The Inter-University Institute (IUI) for Marine Science was established by the Hebrew University in 1968. As the name implies, the institute is open to scientists from all the universities in Israel. Currently it has six resident scientists, comprising three faculty members from the Hebrew University of Jerusalem and one member from each of Bar-Ilan, Ben-Gurion and Tel Aviv universities. Also in residence at the IUI are a few dozen graduate students from all over Israel.
A bluegill sunfish about to catch its prey (the bright object) in Dr. Holzman’s
One of the unique installations at the institute aims to measure the flow around coral reefs. The effects of water motion are inherently observed through daily human experience, but it is another challenge entirely to measure just how fast, and in what direction, the water is flowing. Resident scientist at IUI and faculty member in the Department of Zoology of the George S. Wise Faculty of Life Sciences at Tel Aviv University, Dr. Roi Holzman, uses a tool called Particle Image Velocimetry (or PIV) for this purpose. By using lasers to illuminate the flow and cameras to capture it, PIV not only allows scientists to visualize how water flows but also to accurately measure the speed of the fluid over an entire image.
While setting up these experiments in a lab can be tricky, it is considerably more difficult to make these kinds of measurements underwater. Not only do the camera and laser have to be aligned properly, but they have to be waterproof, with all adjustments made by divers (often the resident scientists and students). As shown in the image below, the proximity of the coral to the laboratory allows researchers to make these detailed flow measurements in a real aquatic environment. Dr. Holzman points out that these investigations are not damaging to the environment in any way and that the skeleton corals being studied (and placed by IUI scientists) were not killed for this purpose. The coral skeletons were obtained by Israeli customs officers who had confiscated them from people attempting to smuggle these sensitive organisms.
The main focus of Dr. Holzman’s research at the institute is how basic functions (such as feeding) affect the body shape and evolution of fish. It is well known that fish struggle to survive just after they hatch, with mortality rates of larval fish as high as 99%. Even though understanding how to help larval fish survive is necessary for both farming and conservation efforts, there are still many unanswered questions about why the mortality rates are so high. For example, it is sometimes assumed that a lack of food causes the high mortality rates, but Dr. Holzman has found that mortality rates do not noticeably change even with ample food supply.
By studying larval fish in the laboratory Dr. Holzman has found that they feed by swimming towards their prey and then “sucking” it in by growing the size of their mouths to create suction. As the fish get older this process becomes easier – but not for the reason one might think. Dr. Holzman’s research shows that slightly bigger fish struggle the same way as smaller fish when the viscosity of the water is increased, so the feeding actually becomes easier as fish grow because of physics and not because of improved technique. A similar analogy is drinking through a straw: It is far easier to drink orange juice through a straw than it is a milkshake. In a similar way, seawater seems more viscous to smaller fish than it does to bigger fish, so even though they feed in exactly the same way it is much easier for a bigger fish to feed.
The efforts of Dr. Holzman and the other scientists at the IUI, alongside the Coral Beach Nature Reserve, help to ensure that this awe-inspiring aquatic environment will continue to prosper and to be enjoyed by future generations. Life under the sea is so much different than it is on land, and we are only beginning to understand its complexity. The research of Dr. Holzman shows how even the simple act of feeding can be a challenge underwater. It is truly a world which must be experienced to be believed.