Have you recently looked up at the night sky and seen…nothing? I went on a trip to Africa last year and as I was climbing Mount Kilimanjaro in total darkness, I saw the most beautiful starry night I have ever seen. That’s when I realised that at home, I can barely see the stars at all.
When we hear the word ‘pollution’, many of us think of carbon dioxide and fossil fuels and scary statistics about global warming. These forms of pollution get the most attention, but there is another pollutant that is quietly cloaking our night sky.
Artificial night light (ANL) is created by man-made sources of light which affect humans and wildlife. For example, street lighting, commercial lighting and residential lighting illuminate the environment and can create sky glow. This lights up the night sky, preventing the visualisation of stars, which is why in many urban areas, we can no longer see constellations like the Milky Way. For the wildlife that use stars to navigate (celestial navigation) or to regulate seasonal behaviours, this can be a major problem. It’s also becoming an issue for us, as about two-thirds of our global population live in regions polluted by artificial light. This is actually affecting our eyesight and approximately one-tenth of our global population now have degraded night adapted vision.
But let’s focus on the wildlife. How bad can artificial light be and how can we really identify the effect it is having? Which animals are we supposed to be focusing on?
A lot of current research is on the effects of ANL on terrestrial animals, as they are fairly easy to monitor. However, there is a large knowledge gap on the effects of ANL on marine ecosystems, as tracking the behavioural changes in these species is logistically difficult. The concern is that ANL is very high along coastal zones because we produce light from coastal development, offshore oil rigs and light houses, and sky glow is created from nearby cities. Approximately 22% of the world’s coastal regions (excluding Antarctica) are affected by ANL and this greatly alters the marine environment. The light illuminates beaches where animals nest and reproduce, creates an artificial horizon along the coastline, and lights from oil rigs illuminate patches of open ocean which attracts and almost traps animals around it.
For my dissertation, I decided to research the literature and find out how ANL is affecting our marine mammals.
Overall, I found that in select marine mammals, particularly seals, ANL disrupts celestial navigation and feeding mechanisms both on-shore and at sea. This is because if seals cannot see the night sky due to sky glow, they cannot navigate during long feeding trips in the open ocean. However, in some rivers and smaller bodies of water, ANL illuminates the seal’s feeding grounds, improving their feeding performance. Although the effects vary, ANL either disrupts feeding behaviour or over-exaggerates it, neither of which are beneficial for the overall food chain and ecosystem.
It is essential that more research is carried out as marine mammals are facing many pressures from human activity, such overfishing, rising sea temperatures and pollution from coastal development. The combined effects of these stressors with ANL could be devastating. We must reduce our light by using lights that are capped to reduce sky glow, and using low pressure sodium lights with lower wavelengths.
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