In many parts of the world, it is no longer real darkness due to artificial light sources. To reduce the detrimental effect of this light pollution on biodiversity, scientists are now calling for the few remaining dark areas to be preserved. Based on the nocturnal activities of the animals, a “dark infrastructure” will be developed that will connect these areas together and provide the animal world with a sufficient number of unlit shelters.
It is not only physical obstacles such as fences, roads, and buildings that restrict animals’ natural behavior and cut their habitats. Light can also do this, if there are too many artificial light sources in the wrong place at the wrong time. Light sources become a real barrier, especially for nocturnal animals that avoid light. Other animals, such as bats, birds or insects, are attracted or irritated by light sources and their nocturnal rhythm is disrupted. In both cases, the light affects the animals in their search for food or in their reproduction, and thus also affects their survival.
Serious impact at different levels
The negative effects of light pollution are now considered a contributing factor to the global decline of insects and the general decline in biodiversity. To protect the animals, Romain Sordello of UMS PatriNat in Paris and colleagues proposed a global network of protection zones to keep them dark at night. On the basis of previous studies, they compiled the known negative effects of light and then came up with solutions to create the so-called dark infrastructure.
As the researchers explain, artificial light at night affects life at different levels – from the genes of individuals to entire ecosystems. For example, it lowers melatonin levels in many organisms, making it difficult for them to synchronize the rhythms of day and night. “Large breasts exposed to artificial light have 49% less melatonin than nocturnal birds, resulting in a change in the innate immune response,” Sordello and colleagues explain. The movement of animals can also be restricted: birds, for example, that use natural light sources such as the moon, the Milky Way, or other stars for orientation at night, can lose their spatial reference points due to artificial light.
Dark havens for wildlife
But despite known and suspected environmental impacts, light pollution has not yet been an evaluation criterion, even in nature reserves. It has been established that between 1992 and 2010 the number of dark areas in Europe decreased by 15 percent, including protected areas. In order to counteract this development, future measures against light pollution should be based on existing green infrastructures, according to the research team’s proposal. These are networks of sites that are designed and managed to contribute to biodiversity conservation and ecosystem stabilization.
According to the researchers, in the future such nets should also include night darkness as a protection criterion and make sure to ensure a high degree of darkness to protect the animals. In order to implement this dark infrastructure, Sordello and colleagues describe a multi-step process: First, light pollution in all its forms and dimensions must be mapped. Then the dark retreats that the fauna of the area need least of all are determined. In the third step, measures will be implemented to maintain these low-light shelters. For example, in the French city of Douai, an audio survey of bat activity in the community area revealed a dark infrastructure. These non-dark objects, which are important to bats, were included in the concept of protection as a series of areas with varying degrees of darkness. The levels reflect the intensity of the bats’ activity.
“Also in Germany, there is a possibility to implement dark infrastructure within green and blue infrastructure with simple investigations and means,” explains co-author Franz Holker of the Leibniz Institute for Freshwater Ecology and Inland Fisheries. Germany already has two licensed park islands, Pellworm and Spiekeroog, and with Fulda the first star city in Europe.
Source: Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB); Specialized article: Landscape and Urban Planning, doi: 10.1016/j.landurbplan.2021.104332