A new study by researchers from the University of Plymouth and their collaborators discusses the dire effect that artificial light at night (ALAN) has on coral reefs. The study is the most recent done as part of the Artificial Light Impacts on Coastal Ecosystems (ALICE) project, and its findings were published in full in Nature Communications.
What's happening?
Light pollution from coastal cities is confusing corals, causing them to spawn outside the optimum times for fertilization.
In normal conditions, moon cycles trigger coral broadcast spawning events annually on certain nights. The timing of this mass synchronized release of both eggs and sperm is critical to the success of fertilization since male and female corals can't move into contact of each other.
Research from the study shows that corals exposed to ALAN are spawning one to three days closer to the full moon than corals on reefs not exposed to light. Coral broadcast spawning events are integral to both the perpetuation of coral reefs and to their recovery from mass bleaching and other damaging events, and spawning on different nights will reduce the likelihood of coral eggs being fertilized and surviving to produce new adult corals.
The ALICE project reports that ALAN "can now be detected above 22% of the world's coasts and will dramatically increase as coastal human populations more than double by year 2060."
The study's authors write, "Climate change-induced mass bleaching events, habitat destruction, fisheries, and pollution combined have reduced coral reef cover substantially since the 1950s. The complete loss of tropical corals is anticipated over the next 100 years."
Why is coral reef loss concerning?
Coral reefs are some of the most biodiverse ecosystems on the planet. Not only do they provide support for 25% of the ocean's marine species, but more than 1 billion people also depend on them for food, income, and protection.
They provide protection from storms and erosion, jobs for local communities, and are an important source of food and medicine. A world without them is a world in trouble.
What can be done to help?
The main solution is a simple one. Thomas Davies, lead author of the study, said, "If we want to mitigate against the harm this is causing, we could perhaps look to delay the switching on of night-time lighting in coastal regions to ensure the natural dark period between sunset and moonrise that triggers spawning remains intact."
Scientists are also finding new ways to help coral reef ecosystems, like growing coral in nurseries and electrocuting coral reefs to supercharge growth.
As individuals, we can dim our nighttime lights wherever we live, reduce our impact on climate change to help the oceans, and stop buying coral jewelry or home decor.
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