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Artificial Light Impacting Coral Reef Species: A Case Study

Artificial Light Impacting Coral Reef Species: A Case Study Image

A species of anemone fish by David Clode via Unsplash.

Each month, IDA’s Director of Conservation, Ashley Wilson, tackles a new piece of scientific research regarding light pollution and breaks it down for us in a blog post.

As a resident of sunny Florida, I spend most of my free time along the beautiful Atlantic coast, soaking up the sun, listening to the soothing sounds of the pulsing waves, and searching for the various clues that wash up on shore and provide a hint of the vibrant life teeming under the water’s surface. Pieces of sea snail shells, clams, scallops, and other various sea life can be an indication of a nearby coral reef. The Florida Reef Tract stretches approximately 360 linear miles from Dry Tortugas National Park west of the Florida Keys to the St. Lucie Inlet in Martin County. It is the third-largest coral reef formation in the world. Yet, these coral reefs border some of the most densely populated cities in the state, and as such, are located nearby areas with high amounts of cumulative light pollution. While we know how light can scatter in the atmosphere and impact terrestrial ecosystems, have you considered how light pollution impacts life below the ocean’s surface?

An international team of researchers from France, the United Kingdom, Chile, and Australia set out to look into this question by studying the impact of long-term exposure of artificial light on resident juvenile orange-fin anemonefish in the lagoon of Moorea, French Polynesia. Anemonefish are an ideal study species due to their intimate relationship with sea anemones, as they completely rely on the anemones to provide food and shelter and cannot leave this habitat, even in the presence of a potential stressor, such as light or sound pollution. The researchers also targeted juvenile individuals as the size and speed at which they grow, as well as the number of individuals that survive to adulthood, are excellent indicators of the health and status of a habitat. 

The results of the study revealed two principal outcomes. First, over the total monitoring period of 23 months, the survival probability of fish exposed to artificial light decreased by 36%. Second, and contrary to the researchers’ expectations, artificial light caused a negative impact on juvenile growth, which was 15%, 21%, and 51% lower in terms of height, length, and weight, respectively. One potential explanation for the decrease in fish survival could be from an abundance of large predatory fish, which have been shown to increase foraging activity under artificial light. Both juvenile fish survival and growth rate may be related to physiological impacts such as stress, sleep deprivation, and increased energetic demand due to the lack of darkness. If juveniles are not able to grow to their full potential, they might be more likely to lose in the competition for space, be more vulnerable to predation, and have a lower chance of producing viable offspring.

For perspective, the levels of illuminance measured underwater at the treatment sites in this study are comparable to shallow fringing reefs exposed to street lighting and hotel lights, which is considerably lower than those produced by LED lights at a port or marina.  Additionally, the presence of artificial light could interact with other stressors, such as agricultural runoff, human disturbance from tourism, land-based sound pollution, or motorboat noise, and work together to increase the impacts of how fish respond. While this study focused on a single species, it is important to note that artificial light may have impacts on entire coral reef communities, as other species may experience similar or even more severe impacts on their physiology, behavior, predation risk, and even long-term population persistence. Fish that live in marine-protected areas (MPAs) are not completely safe from the reaches of artificial light either, as 20% of all MPAs are already exposed to artificial light, and 14.7% are exposed to increasing levels of light pollution1. As such, conversations and policies developed to protect marine environments should include regulations to ensure wasted and unnecessary light does not make its way into these incredibly diverse and remarkable areas.

Long-term exposure to artificial light at night in the wild decreases survival and growth of a coral reef fish

Citation: Schligler, J., Cortese, D., Beldade, R., Swearer, S.E. and Mills, S.C., 2021. Long-term exposure to artificial light at night in the wild decreases survival and growth of a coral reef fish. Proceedings of the Royal Society B, 288(1952), p.20210454.

  1.  Davies, T.W., Duffy, J.P., Bennie, J. and Gaston, K.J. (2016), Stemming the Tide of Light Pollution Encroaching into Marine Protected Areas. CONSERVATION LETTERS, 9: 164-171.

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