Israeli researchers examined the effects of light pollution on reef fish and found that sleep disturbances are not a problem reserved only for humans
By Reot Alon, Zivata - Science and Environment News Agency
In my childhood there were times when I wanted to stay up with the adults instead of going to bed early. The artificial light that humanity invented allows us to stay awake longer, and as a child I was fascinated by that. Today it is already a known matter lighting artificial hurts in circulation the sleep The natural our, but it does not only harm us: a new Israeli study to be presented In the 52th Annual Conference on Science and the Environment On September 25-26 at Ben-Gurion University of the Negev, examine how light pollution affects sleep and DNA damage in reef fish.
Artificial lighting at night is a man-made hazard also known as light pollution. Since the invention of the light bulb and the technological advancement of electricity-based light, we have expanded the use of night lighting and increased its strength as in LED bulbs. "Within the spectrum of light, LED lighting has a high intensity blue wavelength that is stronger. Although for us it is efficient and economical in terms of electricity, this lighting often has an increased biological effect on animals," says Shaf Ben Ezra, a doctoral student in the Faculty of Life Sciences at Bar-Ilan University.
At night they hide among the coral branches which provide them protection. Photo: Shaf Ben Ezra
Besides the constant increase in the intensity of light pollution, there has also been an increase in its spatial distribution - the population is growing and more settlements are being built, so according to Ben Ezra, more areas of the world are affected by artificial lighting. "Most existing research focuses on the effect of artificial lighting on terrestrial environments, and this is because marine research is more limited and complex. That's why our knowledge is relatively little,' she explains. According to her, today it is understood that light pollution also has an effect on marine environments. In her research, under the guidance of Prof. Oren Levy and Prof. Lior Appelbaum, she examined how it affects sleep in fish.
More and more areas of the world are affected by artificial lighting. Photo: Shaf Ben Ezra
shine fish in a negative light
The fish chosen for the study is a greenish chromic (Chromis viridis) which is common in the Indo-Pacific region and on the coral reef in Eilat. According to Ben Ezra, these are shoal fish that live in small and permanent territories (Microhabitats). "During the day they swim in the water column and feed on plankton (creatures that drift in the current of water), and at night they hide among the branches of the coral which provides them with protection and around which their whole life revolves," she says.
To test the effects of artificial lighting on the chromite fish, Ben Ezra and her colleagues conducted research dives during which they collected several shoals together with their house coral of the type Acropora (Acropora). They transferred the shoals to aquariums in the marine laboratory at the Inter-University Institute for Marine Sciences in Eilat, where the fish were given time to adapt. "First we photographed the fish under normative day and night cycles, and later we photographed them under artificial lighting at the same intensity as the existing lighting in Eilat and in accordance with data from light pollution measurements made in the area," she explains.
The researchers fed the footage into a computer, and using a deep machine learning tool, they taught the software to recognize individual fish, allowing them to track each one around the coral during the night. "On normal dark nights, we saw that the interaction between the fish is minimal - they maintain small territories around the coral so that there is some sort of hierarchy - each fish has its place," says Ben Ezra.
According to her, the fish hardly eat at night, and in the hours of darkness they sleep. During the nights when the researchers shined light on the chromite fish, they noticed that the fish use the light to eat. "Additionally, an increase in aggressive interactions was observed - the fish used a larger space around the coral, which led to fights between them over personal territory."
The necessity of sleep outweighs the risk so that the organism can continue to exist. Photo: Shaf Ben Ezra
to wake fish from their sleep
Another finding showed a decrease of about 30 percent in the sleep duration of the chromite fish. But how do you test sleep in fish? According to Ben Ezra, they rely on behavioral parameters, "for example, a decrease in food-seeking activity, being in a resting position (such as lowering the tail down in zebrafish) and homeostasis - a state of balance so that sleep deprivation will lead to late completion of sleep time," she explains. "Another and extremely important measure is a decrease in response to stimuli during sleep. Although this naturally makes them vulnerable to predators, the necessity of sleep outweighs the risk so that the organism can continue to exist.'
According to Ben Ezra, in humans it is possible to check what sleep is with a device called an EEG that scans our neuronal activity, which is a system in the brain made up of cells that transmit information to the body by electrical signals. "During the day, the neurons produce energy and transmit electrical signals to the organs in the body, and this activity creates breaks and damage to the DNA in the cells," she says. "Sleep is important for maintaining our neuronal health, and past studies have shown that it contributes to increased repair of DNA fragments in neuronal cells in fish as well."
"In every cell, DNA fragments can form that are naturally repaired by the body, and it knows how to deal with them as long as they exist at low levels," explains Ben Ezra. "At the end of the day you see an accumulation of the fragments in the cells, and after sleep you see a decrease in their quantity - that is, when the body is at rest it can invest more energy in repairing the DNA damage." According to her, an accumulation of fragments indicates a sleep disturbance, and according to this index, Ben Ezra found that in the chromite fish there is an increase in damage to the neuron cells after a light night compared to a dark night. "We found that the repair mechanism is not fully carried out on lighted nights."
The findings of the study indicate that the sleep quality of the fish is impaired and this has a physiological effect. "Other studies show that light pollution harms the survival of fish, and the accumulation of DNA damage can harm their health and cause them to develop diseases such as cancer, one of the causes of which is broken cells that are not properly repaired," explains Ben Ezra. Light pollution does not only harm fish but also breeding של Coral and ability the survival של deer sea, when the hatchlings (small sea turtles that have just hatched from the egg) get confused by the lights on the beaches and as a result cannot find their way to the sea.
"The night lighting we used is very low, and it simulates what happens to fish in the wild as a result of the illumination of the city of Eilat," emphasizes Ben Ezra. According to her, there are ways in which it is possible to reduce light pollution This is like using lighting with a sensor that turns on only when a car passes by, a change in yellow vs. blue wavelength and low lighting that spreads less in space. "The collection of evidence on the negative effects of light pollution is important because it can help us change policy, and this is possible with the commitment of planning and municipal authorities," she concludes.
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