Artificial night sky causes feeding confusion

On Sunday, Australian citizen scientists used the longest night of the year in the Southern Hemisphere to get together to measure light pollution around the country.

Today, there’s new research from the Northern Hemisphere about the damaging impact of what is often known as artificial starglow.

Researchers from Bangor University and the University of Plymouth in the UK say light originating from cities up to several kilometres away could be having a significant impact on species that rely on the Moon and stars to find food.

It disrupts the lunar compass they use when covering long distances, they suggest, which in some cases can lead to these species travelling towards the sea and away from food, and in others can reduce the chance of them venturing out on forays for food at all.

The project looked specifically at the sand hopper (Talitrus saltator), which is common along European coastlines, but the findings have implications for the wider ecosystems, the researchers say.

“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,” says Plymouth’s Thomas Davies, senior author of a paper in the journal Current Biology.

“Our results show it is already having demonstrable impacts on biological processes that are guided by celestial light cues.”

Thomas and colleagues monitored the sand hopper population on Cable Bay beach in North Wales, a naturally dark location, over 19 nights between June and September last year.

They observed the behaviour of almost 1000 individuals under a range of moon phases and weather conditions, before introducing artificial light that replicated the intensity and colour of skyglow from towns and cities around the coast.

The results showed that artificial skyglow reduced the probability that individuals undertook their migrations during the full Moon under clear sky conditions, and during the new Moon irrespective of cloud cover.

In the absence of artificial skyglow, when the Moon was full and the sky was clear, they migrated in the expected shoreward direction to forage. However, in the presence of artificial skyglow during the same Moon phase and cloud cover conditions, their movements were far more random.

The researchers say this could pose a distinct threat not just to the health of sand hopper populations but also the wider ecosystem, since they play an important role in breaking down and recycling algae washed up on strandlines.