The world gets more light polluted each year. We already know sea turtles getdisoriented swimming to shore to lay their eggs. Even humans are told to avoidbright lights before bedtime and to create dark sleeping spaces that keep outstreetlights. Species across the tree of life rely on constant cycles of lightand dark to eat, rest, and be active at the right times. Now, scientists haveconfirmed that clownfish reproduction is stopped by artificial light.

The study, released earlier this week, exposed breeding clownfish pairs to 12hours of daylight followed by 12 hours under dim artificial lights. Theselight levels simulate the artificial light exposure of near-shore reefcommunities, such as reefs just offshore a small city. The light levels arestill conservative for marine infrastructure, like oil rigs, piers or cruiseships which are increasingly common.

The scientists unexpectedly discovered not a single egg hatched under theartificial light conditions. In comparison, the group of clownfish exposed tonormal light cycles had an 86% hatch rate. Both groups had laid a similaramount of eggs.

Unhatched clownfish eggs can impact other reefs that aren’t near theartificial light because reef fish populations also depend on larvae comingfrom further reefs. A single area of light pollution could lead to impacts tosurrounding reefs that are still relatively dark at night. Another concern islarval coral reef fishes are attracted to light. They could be choosing reefsexposed to artificial light. Their future reproduction will be inhibited.Impacts of artificial light could spread to other reefs, while attractingyoung fish to an environment where their young likely won’t hatch.

The researchers caution that “light pollution would be creating an ecologicaltrap 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 andphysiology, it’s likely that artificial light is disrupting other speciesbeyond clownfish in the marine environment.

Regulations on the type of light and orientation (facing down, rather thanout), may help reduce impacts of light pollution on clownfish and other marinespecies. Similar regulations were successfully implemented on the Floridacoast to help with sea turtle egg-laying, and perhaps a similar solution willbe required for clownfish and other coral reef fishes.

In fact, in this study, the researchers found that impacts on clownfishreproduction disappeared as soon as they returned the clownfish to normallight-dark cycles.

Source: Linh Anh Cat – Forbes

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