The world gets more light polluted each year. We already know sea turtles get disoriented swimming to shore to lay their eggs. Even humans are told to avoid bright lights before bedtime and to create dark sleeping spaces that keep out streetlights. Species across the tree of life rely on constant cycles of light and dark to eat, rest, and be active at the right times. Now, scientists have confirmed that clownfish reproduction is stopped by artificial light.
The study, released earlier this week, exposed breeding clownfish pairs to 12 hours of daylight followed by 12 hours under dim artificial lights. These light levels simulate the artificial light exposure of near-shore reef communities, such as reefs just offshore a small city. The light levels are still conservative for marine infrastructure, like oil rigs, piers or cruise ships which are increasingly common.
The scientists unexpectedly discovered not a single egg hatched under the artificial light conditions. In comparison, the group of clownfish exposed to normal light cycles had an 86% hatch rate. Both groups had laid a similar amount of eggs.
Unhatched clownfish eggs can impact other reefs that aren’t near the artificial light because reef fish populations also depend on larvae coming from further reefs. A single area of light pollution could lead to impacts to surrounding reefs that are still relatively dark at night. Another concern is larval coral reef fishes are attracted to light. They could be choosing reefs exposed to artificial light. Their future reproduction will be inhibited. Impacts of artificial light could spread to other reefs, while attracting young fish to an environment where their young likely won’t hatch.
The researchers caution that “light pollution would be creating an ecological trap for recruiting reef fishes, and this could have significant and broad-scale consequences in areas with extensive pollution”.
Since most life relies on cycles of light and dark to regulate behavior and physiology, it’s likely that artificial light is disrupting other species beyond clownfish in the marine environment.
Regulations on the type of light and orientation (facing down, rather than out), may help reduce impacts of light pollution on clownfish and other marine species. Similar regulations were successfully implemented on the Florida coast to help with sea turtle egg-laying, and perhaps a similar solution will be required for clownfish and other coral reef fishes.
In fact, in this study, the researchers found that impacts on clownfish reproduction disappeared as soon as they returned the clownfish to normal light-dark cycles.
Source: Linh Anh Cat – Forbes