Artificial Coastal Lighting can Disrupt Coral Reproduction

According to a new study, in coastal regions, pollution by artificial light interrupts coral reproduction, which relies on natural light sources to regulate their behavioral, physiological, and biological activities.

The study, which was performed by scientists from the Philippines, Israel, and Germany, was published in the Current Biology journal on November 5^th, 2020.

The study reports that the health of humans and ecosystems can be negatively impacted by strong artificial lighting normally used in yards, office buildings, streets, sports, and industrial establishments.

The team noted that artificial light results in over-illumination, glare, skyglow, and light trespass that impact corals, which are already endangered by global warming.

In 2018, the Intergovernmental Panel on Climate Change published a report warning that even stabilizing global surface temperature increase by 1.5 °C above pre-industrial levels will not stop 70% to 90% loss of coral reefs by 2050.

Disturbance in reproduction is caused by the late production of gametes (female and male germ cells), which are discharged into the water for external fertilization. In corals, the discharge of gametes into the water is controlled by a biological rhythm that functions in unison with the natural light like moonlight.

As part of the study, the team gathered two coral species—Acropora digitifera and A. millepora—from the Indo-Pacific Ocean and categorized them into groups at the Bolinao Marine Laboratory located in the Philippines.

“Each group was composed of 15 colonies from each Acropora species divided randomly into three tanks,” the team wrote in the paper.

Two experimental groups were exposed to illumination by LED lamps, and the control group was subjected to natural moonlight and sunlight rather than artificial light at night. For three months, the LED lamps were turned on every day, from sundown until sunrise.

The findings revealed abnormalities in the production and maturation of gametes in groups that were exposed to artificial illumination, emphasizing the significance of natural moonlight and sunlight to assist normal production of gametes and their synchronized discharge into the water.

“We need to be aware of the impact of light pollution,” stated Oren Levy, the corresponding author of the study affiliated to Israel’s Bar-Ilan University. “In coastal areas near urban districts, there can always be impact [of light pollution]. Therefore, [we] need to plan to use more eco-friendly lights.”

This is yet another example of human activity interrupting ecosystems and animal life-cycles. Light pollution on beaches has been shown to interfere with turtle hatchlings, and now there is the potential that it could also impact coral reproduction.

Gabriel Grimsditch, Marine Ecosystems Expert and Program Management Officer, UN Environment Programme

Grimsditch feels that gaining better insights into and safeguarding coral reproduction cycles is crucial for the survival of coral reefs in a doubtful future. He notes that coral reefs are extremely susceptible to warming sea temperatures and are the first ecosystems to face worldwide extinction due to climate change.

Protecting coral reefs against all other anthropogenic stressors is necessary if we want to boost their resilience and continue to enjoy the huge benefits that they provide to biodiversity and humanity.

Gabriel Grimsditch, Marine Ecosystems Expert and Program Management Officer, UN Environment Programme

Journal Reference:

Ayalon, I., et al. (2020) Coral Gametogenesis Collapse under Artificial Light Pollution. Current Biology. doi.org/10.1016/j.cub.2020.10.039.