Who would have thought that turning on the lights at a beach resort could devastate coral colonies? A new discovery explains the harm while also pointing to the design of Earth’s two natural sources of light.
Several research teams have previously demonstrated that artificial night lighting (ANL) can have deleterious effects on human health1 and ecosystems.2 Now, a new study shows that ANL can have devastating consequences for coral reefs.3
Coral reef organisms depend upon the natural light cycles of sunlight and moonlight to regulate several physiological and behavioral processes.4 In particular, an important cue for coral spawning synchronicity is nocturnal moonlight and the phase of the Moon. Scientists know that as a result of modern technology, ANL in the vicinity of coral reefs often exceeds the Moon’s brightness. Thus, a team of fourteen biologists led by Tel Aviv and Bar-Ilan Universities’ Inbal Ayalon sought to learn of any lighting effects as they conducted laboratory experiments on the two most prevalent tropical coral species: Acropora millepora and Acropora digitifera.
Ayalon’s team took 45 colonies of Acropora millepora and 45 colonies of Acropora digitifera from an unlit site at Caniogan Reef in northwestern Philippines and transferred them all to outdoor tanks at the Bolinao Marine Laboratory, also in northwest Philippines. For each coral species, 15 colonies were exposed only to natural sunlight and moonlight, another 15 colonies to cold white LED lighting (420–480 nanometer spectral range), and the remaining 15 colonies to warm white LED lighting (580–620 nanometer spectral range). The LED lighting intensities were set at levels typical for coral reef ecosystems near urban areas. All six experiments were run for a 3-month period.
Coral Spawning Capacity Disrupted
The experiments yielded the following results. For Acropora digitifera:
3 out of 15 colonies under natural conditions failed to spawn
14 out of 15 colonies under warm LED lighting failed to spawn
15 out of 15 colonies under cold LED lighting failed to spawn
And for Acropora millepora:
1 out of 15 colonies under natural light conditions failed to spawn
14 out of 15 colonies under warm LED lighting failed to spawn
14 out of 15 colonies under cold LED lighting failed to spawn
Ayalon’s team consistently observed worse spawning outcomes for cold LED lighting than they did for warm LED lighting. They attributed this result to cold LED lighting more closely matching the Moon’s spectral radiance than warm LED lighting. Evidently, the Moon phase is the rhythm most masked by ANL. Another contributing factor is that cold LED lighting penetrates sea water more deeply.
ANL does more than just disrupt the spawning capacity of coral species. Separate studies revealed that it also leads to increased oxidative damage, lower antioxidant capacity, and photosynthetic impairment.5 Another study showed that ANL impedes early life stages of corals.6
Researchers have observed that ANL impacts lighting due to cloud cover in a manner opposite to natural lighting. For natural lighting, clouds darken the skies over coral reefs. For ANL, clouds brighten the skies over coral reefs.7
Ayalon’s team completed their paper with an assessment of where coral reefs are at the greatest risk of ecological collapse from exposure to ANL. In order of greatest impending risk, these reefs include those residing in the Singapore Strait, the Gulf of Thailand, the Gulf of California, the Persian Gulf, the Gulf of Aqaba/Eilat, the Gulf of Oman, the South Atlantic Ocean, and the Strait of Malacca—in other words, across much of the globe.
Ayalon’s team notes that LED lighting is exponentially increasing on a global level. Other factors not addressed in their paper include coral reef tourism and coral reef night fishing. Coral reef ecosystems are among the most biologically diverse and productive ecosystems on Earth. They are also extraordinarily beautiful. Hence, beachfront tourist resorts now proliferate along most of the world’s coral reefs. These resorts all have artificial night lighting. Having vacationed at some of these resorts, I have observed many tourists snorkeling at night with bright waterproof headlamps and others who mount lights on their fishing spear guns.
Lessons and Implications of Artificial Light
An obvious next step calls for the need to lessen artificial night light illumination over coral reefs. Coastal cities and resorts near coral reefs need to consider near total blackouts. Cold LED lights should be replaced with warm LED lights with light shields to target light where it is needed and away from sea water and clouds.
Lessening ANL would help more than coral reefs. There is an inverse correlation between ANL and the average number of hours of sleep humans get per night. Humans, like coral species, are more negatively impacted by blue light than yellow, orange, and red light. The same solutions for helping coral reefs would also benefit human health.
For the first time in human history, the majority of humans have not seen the Milky Way with their own eyes. In fact, most of the world’s population live in cities where it is difficult to see more than 30 stars in the sky. In some cities, ANL is so intense and pervasive that not a single star or planet can be seen with the naked eye.
The psalmist states that “The heavens declare the glory of God” (Psalm 19:1). However, the heavens cannot declare God’s glory if people are unable to see the heavens. The inability to see the heavens is one factor, I contend, explaining the rise of atheism among people living in large, densely populated cities.
Personally, I enjoy showing people deep sky wonders through my 11-inch telescope. However, there is a bright street lamp only 3 feet from my property line. Like many astronomers, I have been urging our local governments to sponsor some dark hours throughout the year where all the street lamps would be turned off. Such dark hour holidays would also benefit the few dark sky sanctuaries that exist in some of our national parks and monuments. Wouldn’t it be wonderful if all humans could once again enjoy the night sky like Abraham did (Genesis 15:5)?
This light pollution study reminds us of the two great lights mentioned in Genesis 1:16 and how they are optimally designed. According to Genesis 1:14 the two great lights—the Sun and the Moon—together with the stars “serve as signs to mark seasons and days and years” for the benefit of the animals God creates on creation days 5 and 6. I wrote about some features of the optimal illumination design of the Moon in a previous article. The work by Ayalon’s team adds to this evidence. In this way the heavens still declare the glory of God.
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YongMin Cho et al., “Effects of Artificial Light at Night on Human Health: A Literature Review of Observational and Experimental Studies Applied to Exposure Assessment,” Chronobiology International 32, no. 9 (September 2015): 1294–1310, doi:10.3109/07420528.2015.1073158.
Kevin J. Gaston et al., “Impacts of Artificial Light at Night on Biological Timings,” Annual Review of Ecology, Evolution, and Systematics 48 (November 2017): 49–68, doi:10.1146/annurev-ecolsys-110316-022745; Thomas W. Davies et al., “The Nature, Extent, and Ecological Implications of Marine Light Pollution,” Frontiers in Ecology and the Environment 12, no. 6 (August 2014): 347–55, doi:10.1890/130281; Davide M. Dominoni, “The Effects of Light Pollution on Biological Rhythms of Birds: An Integrated, Mechanistic Perspective,” Journal of Ornithology 156 (December 2015): 409–18, doi:10.1007/s10336-015-1196-3.
Inbal Ayalon et al., “Coral Gametogenesis Collapse under Artificial Light Pollution,” Current Biology 31 (January 25, 2021): 1–7, doi:10.1016/j.cub.2020.10.039.
Paulina Kaniewska et al., “Signaling Cascades and the Importance of Moonlight in Coral Broadcast Mass Spawning,” eLife 4 (December 15, 2015): id. e09991, doi:10.7554/eLife.09991.001; Alison M. Sweeney et al., “Twilight Spectral Dynamics and the Coral Reef Invertebrate Spawning Response,” Journal of Experimental Biology 214, no. 5 (March 2011): 770–77, doi:10.1242/jeb.043406.
Inbal Ayalon et al., “Red Sea Corals under Artificial Light Pollution at Night (ALAN) Undergo Oxidative Stress and Photosynthetic Impairment,” Global Change Biology 25, no. 12 (December 2019): 4194–4207, doi:10.1111/gcb.14795; Yael Rosenberg, Tirza Doniger, and Oren Levy, “Sustainability of Coral Reefs Are Affected by Ecological Light Pollution in the Gulf of Aqaba/Eilat,” Communications Biology 2 (August 5, 2019): id. 289, doi:10.1038/s42003-019-0548-6.
Raz Tamir et al., “Effects of Light Pollution on the Early Life Stages of the Most Abundant Northern Red Sea Coral,” Microorganisms 8, no. 2 (January 31, 2020): id. 193, doi:10.3390/microorganisms8020193.
Christopher C. M. Kyba et al., “Cloud Coverage Acts as an Amplifier for Ecological Light Pollution in Urban Ecosystems,” PLoS ONE 6, no. 3 (March 2, 2011): id. e17307, doi:10.1371/journal.pone.0017307.