Artificial system

New atlas sheds light on the impact of artificial light in the ocean at night

  • Researchers recently published the world’s first atlas that quantifies artificial light at night on underwater habitats.
  • Artificial light from urban environments along the coast can have far-reaching impacts on a range of marine organisms that have evolved over millions of years to be extremely sensitive to natural light such as moonlight.
  • Researchers found that at a depth of 1 meter (3 feet), 1.9 million square kilometers (734,000 square miles) of the world’s coastal oceans were exposed to artificial light at night, which equates to about 3 % of exclusive economic zones in the world.
  • Blue tones from LED lights can penetrate particularly deep into the water column, potentially causing more trouble for underwater inhabitants.

Conservation ecologist Thomas Davies has long known that natural light plays a central role in the life of many marine organisms.

“They use it like a clock,” Davies, professor of marine conservation at the University of Plymouth, UK, told Mongabay in a video interview. “They use it to regulate the timing of particular events like spawning in corals, for example. Marine species can use it as a compass to navigate the environment. And they can use it to guide things like their migrations up and down the water column. “

But until recently, many researchers had failed to consider the potential impacts of artificial light at night on the marine environment, Davies explains. According to him, some experts have even suggested that light pollution is not a serious problem for the underwater world since only small amounts of light reach the depths of the water column. Yet Davies argues that artificial light can have far-reaching impacts on a range of marine organisms – even those that live in the depths – as they have evolved over millions of years to be extremely sensitive to natural light. like moonlight.

In December 2021, Davies and his colleagues published an article in Elementa: science of the anthropocene who introduced the world’s first atlas that quantifies artificial light at night on underwater habitats. The researchers generated the atlas using a range of data sources, including the much-cited atlas of artificial night sky brightness developed by Fabio Falchi and his colleagues in 2016, as well as measurements of light. artificial in the northern Gulf of Aqaba in the Red Sea. , a marine region rich in coral reefs.

A close-up view of the new atlas of artificial light at night under the sea. Image courtesy of Smyth et al.

The research team determined how far and how deep light spectra penetrated the ocean, and also how things like phytoplankton and sediment could alter the optimal properties of water. In addition to this, they set out to determine when artificial light became biologically important enough to have a substantial impact on the marine environment. To do this, they turned to the copepods in the Calanus genus zooplankton which plays an important role in the marine food chain and is particularly sensitive to light. According to another study in Polar biology, Calanus Copepods can respond to moonlight at depths of 170 meters (560 feet) during dark polar nights and are known to perform vertical migrations when there is very little light in the sky. Lead author Tim Smyth, a scientist from the Plymouth Marine Laboratory, told Mongabay in a video interview. water.”

One of the main findings of the article was that at a depth of 1 m (3 ft), 1.9 million square kilometers (734,000 square miles) of the world’s coastal oceans were exposed to artificial light at night. biologically important. This represents more than 3% of the world’s exclusive economic zones, parts of the ocean that stretch 200 nautical miles (370 kilometers) from the coasts of nations. The amount of coastal water affected has decreased to 1.6 million km2 (618,000 mi2) at 10 m (33 ft) and 840,000 km2 (324,000 mi2) at 20 m (66 ft), according to the study.

Smyth says these calculations are probably conservative since the researchers made a number of assumptions, including the premise that all cities would have a light spectrum similar to that of Plymouth, a city of around 260,000 people. The researchers expect that as they refine their model, the impact of artificial light at night on the underwater world will increase dramatically.

A global view of the new atlas of artificial light at night under the sea. Image courtesy of Smyth et al.

The researchers also found that LED light, which uses much less energy than traditional incandescent bulbs and is considered by many to be environmentally friendly, can actually penetrate deeper into the water column, potentially causing no more problems.

“[Cities] are turning to this much more LED-lit spectrum, ”said Smyth. “Now the consequences of this are that the LEDs are much sharper in the blue end of the spectrum. And the problem with blue light is that it is much more energetic and can penetrate much deeper into the water column than into the orange-red area of ​​the spectrum.

Another study found that blue tones in LED lights impacted birds, insects, fish, and sea turtles, but filtered yellow-green and amber LEDs would have a much lower impact.

Davies and Smyth say they hope the Atlas can raise awareness of the impacts of light pollution on the underwater world, and that artificial light will be seen as an additional threat to the marine environment, alongside other stressors such as ocean acidification and plastic pollution. .

“There is now a lot of interest in ecology and conservation on the ability to understand the combined effects of several human stressors on the environment,” Davies said. “And part of that is creating multiple layers of maps of different impacts, and that’s yet another impact that needs to be considered in building this image.”

Banner image: Bright artificial lights on the coast of Hamburg. Image by KarstenBergmann via Pixabay.

Quotes:

Båtnes, AS, Miljeteig, C., Berge, J., Greenacre, M., & Johnsen, G. (2013). Quantify the light sensitivity of Calanus spp. during the polar night: Potential for orchestrated migrations driven by ambient light from the sun, moon or northern lights? Polar biology, 38(1), 51-65. doi: 10.1007 / s00300-013-1415-4

Longcore, T., Rodríguez, A., Witherington, B., Penniman, JF, Herf, L., & Herf, M. (2018). Rapid evaluation of the lamp spectrum to quantify the ecological effects of light at night. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, 329(8-9), 511-521. doi: 10.1002 / jez.2184

Smyth, TJ, Wright, AE, McKee, D., Tidau, S., Tamir, R., Dubinsky, Z.,… Davies, TW (2021). A world atlas of artificial light at night under the sea. Elementa: Anthropocene Science, 9(1). doi: 10.1525 / elementa.2021.00049

Tamir, R., Lerner, A., Haspel, C., Dubinsky, Z., & Iluz, D. (2017). The spectral and spatial distribution of light pollution in the waters of the northern Gulf of Aqaba (Eilat). Scientific reports, 7(1). doi: 10.1038 / srep42329

Elizabeth Claire Alberts is a writer for Mongabay. Follow her on twitter @ECalberts.

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Conservation, Environment, Environmental ethics, Habitat degradation, Cartography, Marine, Marine biodiversity, Marine conservation, Marine crisis, Marine ecosystems, Ocean crisis, Oceans, Pollution, Research


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