The heavy price that corals may pay due to climate change

Global warming affects life in the sea in many ways when it causes a decrease in dissolved oxygen in the ocean water on the one hand, and on the other hand, an increase in the metabolism of marine animals, which further increases their need for oxygen

The coral reef in the Gulf of Eilat. Photo: Prof. Maoz Payne, Bar Ilan University

Corals that are in conditions of lack of oxygen for a long time survive this situation, but pay significant prices for this that endanger the survival of future generations: a decrease in the ability to prey, a growing dependence on the symbiotic algae and a decrease in the processes related to reproduction, according to a new study conducted at the School of Marine Sciences Q. Leon Charney at the University of Haifa. "Even though the coral survives, it pays a heavy price for it and the fear is that any environmental change Another one, especially one that would harm the coral's symbiosis with algae, would harm its ability to cope with the decrease in oxygen. The study teaches us about the heavy price we will pay in the future for climate changes," said Dr. Hagit Kvit from the university, the leader of the study.

Coral reefs have many important roles for marine ecosystems and humans. They provide a living area for about 25% of the marine organisms and contribute to the biological diversity of the marine life system. In addition, the coral reefs serve as the "rain forests" of the sea: the coral lives in symbiosis with algae that are inside its cells and provide it with about 90% of its energy, while they perform a process of photosynthesis.

Global warming affects life in the sea in many ways, when, among other things, it causes a lack of oxygen: the increase in seawater temperature causes a decrease in the oxygen dissolved in the ocean water on the one hand, and on the other hand, an increase in the metabolism of marine animals, which further increases their need for oxygen. "Hence the need for oxygen increases while the concentration of oxygen decreases, which endangers the animals more than the rise in temperature per se. Studies conducted in the past found that some of the extinction events throughout history were probably caused by a similar combination of an increase in temperature and a decrease in oxygen," the researchers said.

In the current study published in the journal Frontiers in Marine Science The researchers Dr. Hagit Kvit, Dr. Assaf Malik, Prof. Samdar Ben Tabo-De Leon, Dr. Eli Shemesh, Dr. Maya Lalazar, Prof. Tali Mas and Prof. Danny Chernov from the School of Marine Sciences requested Charni at the University and Dr. Hanna Rosenfeld from the National Institute for Seas and Lakes Research in Eilat, in collaboration with researchers from China, to monitor the effect of the decrease in oxygen concentration Over time on the physiology and gene expression in Bona-Shanit coral. In the past, the genetic response to a lack of oxygen was tested for 12 hours, which is a relatively short period of time expected to happen in nature. In the studies that tested the effect of 11 days of oxygen deprivation, only the physiological response was measured and not the genetic response. The uniqueness of the current study is that it tested both the physiological response and the genetic response for a long period of time, 14 days, in which the corals were at an oxygen level that is approximately 90% lower than the oxygen level in which they normally live (decrease from a level of 6 milligrams per liter to a level of -0.6 0.3 milligrams per liter). The tests were conducted in three different periods of time: 12 hours, seven days and fourteen days, day and night.

The results of the study show that already in the first 12 hours without oxygen, the coral activated processes that helped it cope with the lack of oxygen: it increased the energy production process that does not depend on oxygen, increased the number of mitochondria to improve the utilization of oxygen in the cells, and also began to increase the extraction of nutrients from the algae The symbionts. However, after a longer time, ranging from one to two weeks, a decrease in the processes related to reproduction was also discovered, mainly a decrease in the amount of sperm production, and a decrease in the production of the burning mechanism, which the coral uses, among other things, for prey and protection. The process of increasing the pumping of the nutrients from the symbiotic algae continued and even increased and at the same time there was an increase in the number of its algae. "The combination of increasing the pumping of nutrients on the one hand and the increase in the number of symbiotic algae on the other hand, increases the coral's dependence on algae. Hence, any change in the sea that harms the algae, such as the warming of the water, may harm the coral's ability to survive conditions of lack of oxygen," said Dr. Quit.

According to the researchers, the research has great significance for understanding the heavy price that will be paid in the future for climate change. The combination of the decrease in oxygen concentrations, the increase in temperature and the increase in the acidity of the sea water may create an increasing burden on marine creatures, and especially on those that are not mobile, such as corals, which cannot escape from areas where there are sudden changes in the sea water. "Understanding the mechanisms affected by each stressor, and those affected by a combination of several stressors together, will make it possible to map the level of damage to the various creatures and will make it possible to determine the policy for dealing with the climate change that we are bringing upon ourselves," the researchers concluded.

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