Light pollution in the Belgian North Sea affects the ecosystem

The effect of nighttime artificial light on marine ecosystems has been studied for several years, but the true effect has long been unknown. Until the end of last year.

An international team of scientists from the United Kingdom, Norway and Israel have designed an atlas that shows how deep and how deep artificial light is at night in seas and oceans around the world. The numbers don’t paint a good picture: Artificial Night Light (ALAN) affects at least 1.9 million square kilometers of sea and oceans, an area roughly the size of Mexico.

Oceanographer Tim Smith: 80% of the Belgian North Sea is affected by underwater artificial light. That’s really a lot”

“The Belgian part of the North Sea is doing poorly,” he says. Tim Smithoceanographer and research chief in the marine biochemistry department at Plymouth Navy laboratory. “From the Belgian North Sea region, 80% below the surface of the water is affected by artificial light. That’s a lot already.” This puts Belgium in questionable seventh place.

In Europe, only the French part of the North Sea scored worse in relative terms. “In absolute numbers, that’s not much,” Smith explains. “Belgium has a relatively small exclusive economic zone (waters with certain state rights, ed.): about 3450 square kilometers. The Iranian part of the Persian Gulf, for example, 120 thousand square kilometers is affected by artificial light.”

“The amount of light and the depth that penetrates under the water’s surface depends on many factors such as sediment or the amount of phytoplankton,” Smith explains. “In the clear waters of the Mediterranean, artificial light can penetrate to great depths, sometimes as much as 40 metres. In the sediment-rich waters off the coast of Belgium, surface-level light pollution is very strong, but when you go a few meters deep, the light disappears. “.

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This is also reflected in the team’s calculations: 70% of the Belgian North Sea is still affected by artificial light to a depth of about ten metres. Artificial light penetrates deeper than ten meters on only 7.5% of the total surface.

Impact on marine life

In this way, the effect of ALAN penetrates to the base of our food chains. Smith and colleagues used copepods as a reference in their study. “Copipods (Copepoda) are zooplankton, and are a major species in the marine environment.”

“Phytoplankton is at the base of the food chain in the sea and one level above it comes the zooplankton. The zooplankton feed on the phytoplankton. The zooplankton in turn are food for the larvae of fish and fish. In this way, zooplankton are also a major species of animals. The entire food chain, as well as For fishing, for example,” says Smith.

Exposure to artificial light has far-reaching consequences for many marine species, the food chain, and thus the ecosystem

Zooplankton can see very low intensity light. During the day, the crustaceans stay deeper under the sea to make themselves as invisible as possible to predators. On the other hand, at night, they come to the surface to feed on the phytoplankton that float there.

Smith’s colleagues studied the effect of artificial light on this species through experiments during polar nights in the Arctic Sea. By turning off the light on their ship themselves and then turning it back on, they were able to record the dramatic dive made by the zooplankton to avoid the ship’s light.

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The effect of the abundance of artificial light at night is unimaginable: zooplankton will also surface less at night to feed on phytoplankton, which in turn can have disastrous consequences for the food chain.

Previous scientific research has also shown that exposure to artificial light has far-reaching consequences for different marine species. “Coral reefs, for example, depend heavily on lunar cycles for their reproduction,” Smith explains. “But instead of natural cycles where the night light gradually increases and decreases, you now have a new human signal: once it gets dark, the light shines everywhere, and it stays shining all night. Thus, the corals can reproduce a lot. A much more difficult time.”

Night artificial light also has a multiple effect on other invertebrates, fish and turtles: from reproduction to migration, and even on the physiology of some species.

Megan Vasquez

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