Researchers at the University of Oldenburg in Germany have concluded that pollution-related darkening of coastal waters in the world’s oceans poses a serious threat to ocean food chains.
Since 2016, researchers with the Coastal Ocean Darkening Project at the University of Oldenburg have been investigating how pollution and runoff alter the color and clarity of coastal waters and assessing the degree to which this darkening jeopardizes the health of ocean ecosystems. As Hakai Magazine reported in February 2021, the Project’s research shows that coastal darkening has “the potential to cause huge problems for the ocean and its inhabitants.”
Coastal darkening is usually the result of introducing organic matter, such as decaying plants or loose soil, into an aquatic environment. Sometimes heavy rains wash organic matter into oceans and rivers. But more frequently, organic matter is introduced into aquatic environments by human activity, such as boating or the application of fertilizers to farmland. When fertilizer is washed away and ends up in the oceans, it causes an algal bloom that creates a light-blocking layer on the water’s surface. Boating causes silt to be kicked up, which can likewise obstruct light to the marine life beneath it.
Light-blocking layers of organic material affect sea life in two ways. First, they prevent many types of sea life from gathering food. These impacts begin with phytoplankton that require light for photosynthesis, and extend up the food chain to impact other species that feed on plankton. As documented by researchers at the University of Oldenburg, a lack of light means a lack of food for small fish and other low-level consumers, which in turn means these low-level consumers have a reduced level of nutritional value for the organisms that feed on them. This drop in nutritional value in low-level consumers leads to reduced food quality and compromises coastal organisms’ trophic efficiency—scientists’ term for efficiency of energy transfer between different links in a food chain. At the same time, a lack of adequate light directly prevents many larger fish and other ocean predators from hunting their prey (although it should be noted that this lack of light actually benefits some organisms, such as jellyfish, that do not rely on light to hunt). On a large scale, these changes in ocean ecosystems could eventually lead to shortages of fish not only for humans, but also for other species that depend on them for sustenance.
The second main problem stemming from light-blocking organic material is that sunlight normally serves to break down toxic chemicals in the water. Decreased light compromises this process, resulting in higher contamination levels, which further damages oceanic food chains.
As of May 2021 there has been no coverage whatsoever by corporate media of coastal darkening. Hakai Magazine, a web journal focused on coastal science and societies, published the first news account of the phenomenon on February 10, 2021. Doug Johnson’s Hakai article was reprinted four days later in The Atlantic. Since then, environmental news outlet EcoWatch has published a short article on the problem based almost entirely on Johnson’s reporting, and the Europe-based public affairs website Modern Diplomacy carried a brief commentary on the combined effect of sea level rises and coastal darkening that referenced the work of the Oldenburg University research team.
Doug Johnson, “The Environmental Threat You’ve Never Heard Of,” Hakai Magazine, February 10, 2021.
Student Researcher: Victor Rodriguez (North Central College)
Faculty Evaluator: Steve Macek (North Central College)
Illustration by Anson Stevens-Bollen.