They look like a colorful stone or a strange plant, they can be found in oceans around the world and their best friend is probably a microscopic algae. Corals are not only very important animals in nature – they are also fascinating. To get to know them in depth – even without diving in Eilat – we spoke with Dr. Tom Schlesinger from the School of Zoology, Faculty of Life Sciences and Steinhardt Museum of Natural History, Tel Aviv University and the Interuniversity Institute for Marine Sciences in Eilat. He told us how they create mesmerizing reefs with their beauty, why they are so sensitive to climate change, how they symbolize the damage of global warming and how childhood in the southern city led him to engage in research on this wonderful underwater world.
Let's start with the basic question. What is coral? A stone, a plant, an animal?
"Coral is a relatively simple animal and is one of the most ancient and basic animals we know of – ones that have lived on Earth for hundreds of millions of years."
"Corals live only in marine environments and their species can be found in all corners of the world – including in the Mediterranean Sea and off the coast of Antarctica. There are thousands of species in different shapes, colors and sizes. There are corals that live in the sea in shallow areas and those that prefer depths of even thousands of meters. Some of them are more sensitive and some of them are less sensitive to changing environmental conditions, and despite all the differences, most of them have very similar characteristics and properties."
What is so special about coral reefs?
"Coral reefs are some of the richest and most diverse ecosystems on Earth. Although they cover only a small portion of the ocean floor, they house and support about a quarter to a third of marine animal species. They provide food sources and shelter for countless creatures such as invertebrates, fish, and more."
Why are stony corals so important?
"Stony corals are the 'contractors' of coral reefs – they build the structures on which the entire ecosystem is based. The corals secrete a calcareous skeleton that remains in the reef after they die. New corals grow and settle on top of these skeletons, and thus the reef continues to exist and grow. We can say that this skeleton was built thanks to cooperation with microscopic algae that live in the coral tissues: the coral provides them with a home, they perform photosynthesis and in return provide the coral with essential materials and energy. In some corals, this relationship does not exist, but in stony corals, which build the world's reefs, this relationship is critical and without them a coral reef would not exist. Similar to the way trees build the forest, corals actually create the environment in which they live. Without corals, the tropical reef we know would not exist, and without it – such a rich underwater world would not exist."
Where can you find coral reefs like the one in the Gulf of Eilat? What makes it special?
"Coral reefs exist mainly in tropical areas – between latitudes 30 degrees south (Australia region) and 30 degrees north (Gulf of Eilat region). In other words, the reefs in Eilat sit on the northern edge of their distribution range. The presence of the reefs in our area in a desert environment is quite unique. The Red Sea, within which the Gulf of Eilat is also located, is a 'warm' and relatively salty sea. Unlike tropical areas, there is not much rainfall in the Gulf of Eilat region and there is almost no flow of streams into the sea. Therefore, the water is very clear, and the high evaporation increases the salinity of the water."
"The entire Red Sea, especially in its northern region, is very rich in endemic species that are unique to this region. That is, it has corals, fish, and invertebrates that you won't find anywhere else. In addition, because the reef in Eilat is made up of corals that are relatively small in size compared to corals on other reefs in the world, more species live per square meter - which increases the diversity of species."
"In the distant past, the Red Sea was cut off from the Indian Ocean and was actually a closed, salty, warm lake for a time. After the Red Sea reconnected with the Indian Ocean, only the corals that survived the relatively harsh conditions of heat and salinity were able to penetrate north. In other words, the corals underwent 'selection' and are therefore probably slightly more resistant to warm seawater, compared to corals in other areas."
How are corals affected by the climate crisis?
"Coral reefs respond dramatically to global changes. They are suffering from many environmental impacts, including direct impacts of the climate crisis. Even if the coral reef can cope with a single local difficulty to some extent, today we are dealing with complex situations with several layers, and coping is becoming more difficult. When talking about climate change in the marine environment, the two main threats are warming sea water and ocean acidification."
"The oceans have been warming for decades, at an accelerating rate. It's not just about the average temperature rising, but the fact that events Extremists are becoming more common. Ocean heat waves are spreading and occurring with increasing frequency and intensity, and over larger areas. This warming is causing stony corals, which already live at the edge of their suitable temperature range, to exceed their tolerance threshold. Extreme or prolonged heat can quickly lead to mass bleaching and death of corals, and subsequently to the disintegration and collapse of the reef. Many coral reefs around the world have already suffered severely from massive bleaching events. Coral bleaching is a process in which corals lose their [microscopic] algae and remain white and weakened, which puts the entire reef at risk. Although the sea water in the Gulf of Eilat is warming at a fairly rapid rate, a massive bleaching and death event has not yet been observed. However, in the past year, we have seen in Eilat for the first time and to a limited extent Coral bleaching "A finding that requires continued close monitoring."
Why did you decide to research corals?
"I grew up in Eilat and the sea was an integral part of my daily landscape. The amazing desert around me is quiet, static and monotonous compared to what you see below the sea surface where there is a colorful, vibrant and lively world. From a young age I loved being in the sea, snorkeling and diving. As a child I would walk around the beaches, turning over stones and looking at what animals were hiding there and what they were doing. Later I worked on the underwater observatory's diving team and did a variety of underwater work and biological treatments. I worked a lot with animals like sharks and sea turtles – which are certainly charismatic and interesting creatures – but it was the corals that captivated and captivated me more than anything else. I loved growing corals, taking care of them and patiently watching for a long time how they reacted and changed. Despite their simplicity, many things in their lives were a mysterious and complex puzzle to me, and it was simply a challenge and interest to me. Even today as a researcher, I sometimes feel like the same child who turned over stones on the beach – only now I am equipped with the tools. "Scientific ones that help me understand and decipher their secrets."
What is your research about?
"I am an ecologist and most of my research deals with the question of how diverse environments such as coral reefs are formed, preserved or disappear. Together with all my research students, my lab deals with a variety of topics related to corals and the coral reef as a complex ecosystem. For example, we deal with the work of identifying, documenting, and describing coral species (taxonomy). This is important because if we do not know and understand what we have, then we will not be able to know what may disappear. We need to understand the changes that are occurring in biodiversity."
"In addition, we study deep coral reefs. Although it may sound surprising, even at depths greater than 40–50 meters where there is little light, we find coral reefs teeming with life."
It sounds like corals have a special survival ability.
"Absolutely. Another important topic that we study a lot has to do with coral reproduction and distribution. The future of species – whether corals or humans – depends largely on their ability to reproduce and produce offspring. Because corals are bottom-attached animals and cannot move to search for mates, they have developed a wide variety of fascinating reproductive methods."
"Most stony corals are 'monoecious' (or 'hermaphrodites'). That is, each individual is both male and female – it produces both sperm and eggs at the same time. There are also coral species that, like most mammals, are 'dioecious' or 'dizygotic', meaning individuals are either male or female. In addition to these, there are species that switch sexes during their lives so that at one time they will release eggs and at another time they will produce sperm."
"Most stony corals reproduce through external fertilization, which is accomplished by the mass release of reproductive cells into the water. This usually occurs in perfect synchronization between individuals of a particular species, creating the appearance of a colorful underwater blizzard. Other species undergo internal fertilization, in which sperm cells from nearby corals are absorbed and embryonic development occurs within the coral. All of these reproductive phenomena, which provide the corals with the only possibility of dispersing themselves over long distances, are a central focus of research in my laboratory."
How do coral reefs benefit humans?
"Coral reefs provide us with critical ecological services. They are a habitat for a huge variety of fish and other animals, which serve as a vital source of food in many parts of the world. They are also an important tourist attraction and a significant source of income. In addition, coral reefs provide a natural line of defense against storms and waves. A significant portion of the world's population lives near the coastline, and reefs - which are often located parallel to the coasts - absorb waves and protect the land from weathering and damage. If the reefs disappear, our sources of food, income and protection will also disappear."
And despite their importance, corals and reefs are in danger.
"That's right. The marine environment in general and coral reefs in particular are subject to many pressures such as climate change, warming sea waters, pollution, overfishing, irresponsible tourism, and more. At a local level, human-sourced pollutants are discharged into the sea around the world: for example Sewage discharged into the sea, fertilizers and pollutants that are washed from the soil with rainwater into the sea, and plastic and its breakdown products such as Microplastics that accumulate in the sea and on the beaches. In Eilat, for example, we are very concerned about the increase in oil flow at the terminal Ktsa'a "And the enormous damage that could be caused in the event of an oil leak."
"In such ecosystems, there is a complex web of life in which each individual species has a role. If there are fewer sea urchins and herbivorous fish that eat algae, then the algae may 'go wild' and grow out of control. This may prevent the corals from settling on the reef and growing. The result is that every year, more species of coral are defined as endangered species on a global level, with increasing levels of severity. Furthermore, we may not yet know all the possible damages. For example, there may be disruptions in the reproductive and growth processes as a result of hormonal effects of substances that accumulate in seawater. Even if the reef seems strong and durable to us and it seems that corals can adapt in all kinds of ways, they may be very fragile. Sometimes small changes may disrupt their activity and significantly harm them."
"A coral reef is a complex, sophisticated and beautiful natural system – but also sensitive and vulnerable. I believe that the better we get to know it, the more we will understand and know how and how important it is to preserve it."
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