The safety of the water is no protection against the effects of artificial light, finds a study recently published in Ecological Applications. Adding light to a stream in Ohio changed the abundance of invertebrates such as spiders and insects.
Scientists have been documenting an ever-increasing list of effects from light pollution. Insects, for instance, can directly be killed by hot lamps. Or there might be more predation of them — bats have been spotted feasting on bug buffets near artificial lights. Other animals, including us, can have their circadian rhythms disrupted.
Those effects can have a cascade of impacts throughout an ecosystem. To determine what those might be in a stream, Lars Meyer and Mazeika Sullivan of Ohio State University set up an experiment on Slate Run, an offshoot of the Scioto River near Columbus, Ohio. After measuring light levels in urban areas adjacent to streams — including restaurants, sports arenas and roads — the team flooded areas of the stream with similar levels of light at night. Weeks later, they collected emergent insects and terrestrial arthropods and surveyed spider webs, comparing those collections to ones made before the addition of artificial light.
In the lighted areas, Meyer and Mazeika found a 44 percent decrease in one family of orb-weaving spiders, a 76 percent decrease in the body size of emergent insects and a 309 percent increase in the size of terrestrial arthropods. That last category includes predators and scavengers such as rove beetles and wolf spiders that, like bats, may be attracted to lit areas where they can munch on the abundance of invertebrates that are directly drawn to the light.
The decrease in body size of emergent insects might also be the result of predation, the team writes. Many of the fish species that feast on insects are visual predators, they note, and would probably eat the biggest insects they can see, thus pulling them out of the food web and the scientists’ collection efforts.
As for the spiders, well, they seem to lose out on several levels. Artificial light is helpful for terrestrial predators such as birds, and spiders may be losing prey to competitors. The higher levels of light may make it harder for spiders to hide, leaving them more vulnerable to getting eaten. And to make life even harder for the spiders, high light levels might make the ventrum spots some species use to lure prey less effective. Artificial light is definitely not a spider’s friend.
“As the world’s populations continue to urbanize, the potential for [ecological light pollution] to influence communities and ecosystems at broader spatial scales also increases,” the researchers write. There’s still a lot of research that has to be done to figure out exactly how artificial light is affecting the world’s ecosystems, but there’s enough evidence at this point to realize that light is really messing up a lot of organisms.