New atlas illuminates impact of artificial light in the ocean at night – Mongabay.com
- Researchers recently released the first global 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.
- The 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, equivalent to about 3% of the world’s exclusive economic zones.
- Blue tones from LED lights can penetrate particularly deeply into the water column, potentially causing more issues to underwater inhabitants.
Conservation ecologist Thomas Davies has long known that natural light plays a pivotal role in the lives of many marine organisms.
“They use it as a clock,” Davies, a lecturer in marine conservation at the University of Plymouth, U.K., told Mongabay in a video interview. “They use it to regulate the timing of particular events like broadcast spawning in corals, for example. Marine species can use it as a compass to navigate around the environment. And they can use it to guide things like their migrations up and down the water column.”
But until recently, many researchers hadn’t considered the potential impacts of artificial light at night on the marine environment, Davies says. According to him, some experts have even suggested that light pollution isn’t a serious issue 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 deep-dwelling ones — as they’ve evolved over millions of years to be extremely sensitive to natural light such as moonlight.
In December 2021, Davies and colleagues published a paper in Elementa: Science of the Anthropocene that introduced the first global atlas that quantifies artificial light at night on underwater habitats. The researchers generated the atlas by drawing on a range of data sources, including the highly cited atlas of artificial night sky brightness developed by Fabio Falchi and colleagues in 2016, as well as measurements of artificial light in the northern Gulf of Aqaba in the Red Sea, a marine region rich with coral reefs.
A close-up view of the newly developed atlas of artificial light at night under the sea. Image courtesy of Smyth et al.
The research team figured out how much, and how deeply, light spectrums were entering the ocean, and also how things like phytoplankton and sediment could change the optimal properties of the water. On top of 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 copepods in the Calanus genus, zooplankton that play an important role in the marine food web and are 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 make vertical migrations when there is very little light in the sky.“In the paper, we talked about a ‘critical depth,’” lead author Tim Smyth, a scientist at the Plymouth Marine Laboratory, told Mongabay in a video interview. “And that critical depth is basically the light sensitivity of a zooplankton — so a copepod organism in the water.”
One of the key findings of the paper …….