By 2060, coastal populations are estimated to more than double, bringing more artificial light at night to previously dark areas near the shore. From increased blood sugar and heart rate in humans to confusing hatching in sea turtles, light pollution has been shown to disrupt various coordinated biological functions in marine organisms.
In a new global map of ocean light pollution, researchers have delineated large regions of the ocean lit by “artificial light at night,” or ALAN. The light, mostly produced by urban coastlines and offshore oil complexes, is strong enough to light up deep in coastal waters, possibly altering the behaviors of sea creatures that thrive in the dark, reports Carolyn Gramling for Scientific News.
The study results show how far light pollution can affect the depths of the ocean and which marine species are most likely to experience a biological response. Map details were published in Elementa: Science of the Anthropocene in December 2021.
The research team modeled the data collected by two satellites. One satellite represented nighttime light pollution and the other tracked the color of the ocean by capturing the optical properties of water. Each dataset included onboard artificial light measurements; monthly light-scattering phytoplankton and sediment data collected between 1998 and 2017; and simulations of how light travels through water, Scientific News reports.
Together, the two datasets estimate how nighttime light pollution above water is absorbed below the surface, reports Sara E. Pratt for NASA. Earth Observatory. After analyzing the data, the scientists found that the light penetrates three feet below the surface for about 735,000 square miles. Other regions absorbed light to depths of 33 feet, 66 feet, and more.
Not all ocean dwellers are light-sensitive, so the study focused on analyzing copepods, tiny crustaceans that are essential components of the food web, and using light signals to regulate their biological functions. Copepods rely on sunlight or moonlight as a signal to hide deep in the water from predators. Tiny organisms also use moonlight to determine when to move up and down the water column to feed, for Earth Observatory.
Study author Tim Smyth, an oceanographer at Plymouth Marine Laboratory, says Earth Observatory that the depth to which light penetrates ocean waters depends on the intensity of the lighting above the water as well as the clarity of the water. For example, the sea water near Malaysia is so clear that nighttime light pollution can reach depths of over 40 meters. Certain areas of the ocean vary in clarity from region to region during different seasons when phytoplankton bloom or the presence of visible sediment increases, for example Scientific News.
Due to coastal development and its heavily populated coastal cities, the Persian Gulf and the western coast of Saudi Arabia were the two places with the highest levels of light pollution. Together these areas accounted for light levels reaching up to 50 meters deep in some areas, Scientific News reports. The team also found that efforts to replace lights with energy-efficient LEDs can also have a negative effect on ocean ecosystems.
“The effects of artificial light in marine ecosystems should be a real focus for global change research,” Smyth said. Earth Observatory.