Before we dive in to look at how light pollution can impact coral reefs, let us first understand their importance and role in maintaining underwater ecosystems. From the picture below, coral reefs provide an ecosystem for many marine species, many of which rely on these coral reefs for protection.
Image 1. Importance of coral reefs
However, with the growth of human activities and development of new lighting technologies, artificial light has significantly altered the natural cycles of day and night light which adversely affects symbiotic and reproductive processes of coral reefs. Corals that are exposed to ecological light pollution (ELG) suffer from around 25 times more distinctively varied expressed genes that aid in the regulation of cell cycle, proliferation and growth. Because these corals are very much photosensitive (their sensitivity and response to light), they are vulnerable to ELG especially since they are often found in shallow, clear waters where light can penetrate through easily.
So how exactly do corals sense light in their surroundings?
Just like the retinas in our eyes, these corals use light sensing molecules called cryptochromes-proteins that help convert light. Light is crucial to these corals not only for photosynthesis and calcification but they also rely on moonlight to synchronize spawning. Click on the video to understand and witness the significance of coral spawning.
However, with artificial light that alters spawning cycles of corals, the inability of the corals to detect moonlight may cause them to stop spawning. This is because the corals rely on moonlight for the release of eggs and sperms when corals spawn. This has detrimental effects to the long-term health and continuity of coral reefs.
Apart from spawning, light pollution can also result in inefficiency in the way corals photosynthesise.
From the figure above, light pollution has caused a stark decrease in photochemical efficiency, especially for the Stylophora pistillata, a scleractinian corals species from the Red Sea.
With the effects of global warming such as increase in sea surface temperature and ocean acidification, these corals are placed into more and more stressful environments which they might be unable to adapt to in time. As coral reefs require a dark period to recover from any stress from the environment, the exposure of artificial light further impedes the potential for these corals to react and adapt to harsh environments. This means that more attention would need to be paid to protect and prevent these “underwater gardens” from diminishing. Saving the coral reefs has an even greater importance when we think about the myriad of other sea creatures which have called these coral reefs their home.
Stay tuned for more!
Jean
References:
- Reef Conservation International. (2017) https://reefci.com/2017/08/11/5-amazing-facts-about-coral-reefs/
- Rosenberg, Y., Doniger, T. & Levy, O. Sustainability of coral reefs are affected by ecological light pollution in the Gulf of Aqaba/Eilat. Commun Biol 2, 289 (2019).
- Oren, L., Laura M,, Jennifer I. C. Benichou, Cécile R., Eric B., Renaud G., & Christine F. (2020). Artificial light at night (ALAN) alters the physiology and biochemistry of symbiotic reef building corals. Environmental Pollution, 266 (2).
- Natural History Museum. Unlocking the secrets of coral spawning. https://www.youtube.com/watch?time_continue=142&v=zuHzNRynSLc&feature=emb_logo
- Phys.Org. (2003). Scientists warn light pollution can stop coral from spawning. Retrieved from https://phys.org/news/2015-12-scientists-pollution-coral-spawning.html