With the onset of festive season and winters, the conversation around air pollution has once again become omnipresent. However, little is talked about the ill-effects of light pollution.
A recent study published in Current Biology has pointed out how the natural reproductive cycles of corals living in coastal regions are being threatened by artificial light pollution. Marine organisms, especially colonies of corals, rely on the natural cycles of sunlight and moonlight to regulate their behaviour and biological processes.
But with artificial light spilling into the ocean from street lamps, billboards and buildings, these internal clocks of corals are being disturbed.
Researchers have found that coral exposed to LED lighting are laying eggs at the wrong time, which is preventing them from successfully reproducing. The team of researchers created a map of the oceans that are most affected by artificial light based on their studies which includes the Caribbean Sea and the Pacific and Indian Oceans.
The Gulf of Aqaba in the Red Sea is almost 47 per cent brighter at night than it would be naturally and up to 60 times brighter in some places. Paper author and biologist Oren Levy of the Bar-Ilan University in Israel said, the daily light-dark cycle arising from the earth's rotation is crucial to marine biology. He mentioned that due to the high rate of urban development in marine coastal areas around the world, light pollution could further threaten coral communities' populations, which are already under severe degradation due to global warming and climate change.
Corals reproduce by releasing sex cells called gametes into their surrounding water at the same time in a process known as 'external fertilisation'. With the combination of biological and environmental factors, synchronised spawning is ensured.
Professor Levy and colleagues, in the recent research, studied two coral species from the Indo-Pacific Ocean, Acropora digitifera and Acropora millepora. The group transferred 90 coral colonies into outdoor tanks, filled with seawater, that were exposed to natural sunlight and moonlight. They then divided the corals into three groups, each containing 15 colonies from each of the two species.
One group was exposed only to the natural light while one was exposed to warm LED lamps and one to cool LED illumination. Scientists found that corals exposed to LED light experienced a delay in production of eggs and sperm in comparison to the corals left under natural light alone. It was inferred that solar and lunar light cycles are essential in how the corals schedule their synchronised sex cell discharges.
Rapid population growth in coastal regions has led to an increase in the amount of LED lighting affecting the oceans, the researchers said. LED lighting gives off a lot of blue light that penetrates deeper into the water. To conserve coral reefs located near urban areas, administration must consider the impact of artificial light.