Artificial skyglow poses major threat to coastal ecosystems

Experts at the University of Plymouth have found that the glow of artificial light along the world’s coastline, also known as artificial skyglow, is interfering with the ability of some animals to properly navigate and locate food. 

Species like the sand hopper depend on the position of the moon and the brightness of the night sky to guide their nightly migrations. Commonly found on the European coast, the sand hopper spends the daylight hours buried in the sand at depths of 10 to 30 centimeters, and ventures out at night to feed on decaying seaweed.

The research team monitored the sand hopper population on Cable Bay beach in North Wales for 19 nights, observing the behavior of almost 1,000 individuals under a range of moon phases and weather conditions. Next, the experts introduced artificial skyglow that mimicked typical levels from nearby cities.

The study revealed that artificial skyglow alters the lunar compass used by sand hoppers to navigate across long distances. The interference from artificial light caused some sand hoppers to think it was still daylight and remain underground, while others traveled away from food and toward the water. 

The study authors explained that sand hoppers play an important role in breaking down and recycling algae washed up on the shore, which means that artificial light poses a distinct threat not just to the sand hoppers themselves, but also to the wider ecosystem.

The research was conducted as part of the Artificial Light Impacts on Coastal Ecosystems (ALICE) project funded by the Natural Environment Research Council. Study senior author Dr. Thomas Davies is the principal investigator on the ALICE project. 

“Skyglow is the most geographically widespread form of light pollution. Surveys have shown it can currently be detected above 23% of the world’s coasts nightly, and with coastal human populations set to at least double by 2060 its effects are only going to increase. Our results show it is already having demonstrable impacts on biological processes that are guided by celestial light cues,” said Dr. Davies.

“Through the ALICE project, we are finding increasing evidence that light pollution from coastal cities can influence marine species inhabiting nearby beaches, rocky shores and even the seafloor. These results highlight how pervasive city lighting could be in shaping the ecology of coastlines kilometers distant from their nearest urban centers. They also highlight the potential for artificial skyglow to impact other species that undergo migrations using the moon as a compass.”

Dr. Davies noted that even though our understanding of the wildlife impacts of street lights has improved dramatically in recent years, artificial skyglow has been largely overlooked. He said more work is urgently needed to investigate the extent to which artificial skyglow is shaping the natural environment.

“It is easy to forget the critical influence of the moon in guiding many organisms’ movements,” said study co-author Professor Stuart Jenkins. “However, we are increasingly realising that by disrupting patterns of night time lighting, we are potentially reducing the ability of animals to navigate. This new research on the shores of North Wales shows clearly that very low levels of artificial light can have far-reaching effects on coastal marine species.”

The study is published in the journal Current Biology.

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By Chrissy Sexton, Earth.com Staff Writer