Thanks to Light Pollution, We’re Losing Nemo

Light pollution has a devastating effect on clownfish populations, a new study published in the journal Biology Letters suggests.

As Jenny Howard reports for National Geographic, researchers led by Emily Fobert, a marine ecologist at Australia’s Flinders University, have found that artificial light at night (ALAN) prevents clownfish eggs from hatching—in other words, the real-life counterparts to Finding Nemo’s protagonist may spawn progeny that never make it past the embryo stage.

According to Agence France-Presse, some 23 percent of Earth’s land (excluding the poles) experiences ALAN on a regular basis. Twenty-two percent of coastal regions receive a similar degree of artificial illumination, with light emanating from sources such as housing developments, promenades, ports, harbors and dockyards. Per Cosmos’ Amelia Nichele, scientists say the planet is becoming artificially lighter at a rate of 2.2 percent per year.

“The correct functioning of most natural systems fundamentally relies on light days and dark nights,” Fobert tells AFP. “But the presence of ALAN can mask these natural light rhythms, and interfere with the behaviour and physiology of individual organisms.”

To gauge the effects of human-made light, Fobert and her colleagues observed 10 pairs of clownfish in a lab. Half of the couples experienced natural light levels, or 12 hours of light and 12 of darkness, while the other half experienced low levels of LED light that was roughly on par with the light pollution produced by an average coastal town throughout the night.

Although members of the latter group spawned fertilized eggs at the same rate as the former, none of the eggs exposed to artificial light hatched. Comparatively, Roni Dengler writes for Discover magazine, 86 percent of eggs in the control group hatched.

Interestingly, the light-exposed eggs hatched normally as soon as the scientists removed the overhead LED.

“The presence of light is clearly interfering with an environmental cue that initiates hatching in clownfish,” Fobert explains in a press release. “The results indicate increasing amounts of light have the potential to significantly reduce the reproductive fitness of reef fish who settle in a habitat near shore lines.”

Per AFP, young clownfish set out in search of a new home shortly after birth. Upon choosing a habitat, the animals often stay there for life. As Karen Burke da Silva, study co-author and director of the conservation organization Saving Nemo, tells National Geographic’s Howard, it’s hard for clownfish to move once settled because they are poor long-distance swimmers and most nearby anemones are already occupied by other members of the species. If a seemingly promising habitat turns out to be a hotbed for ALAN, there isn’t much that a would-be clownfish parent can do.

According to the press release, artificial light likely compromises clownfish’s natural spawning rhythms. Clownfish embryos typically hatch after dusk in order to avoid daytime predators; Dengler of Discover further notes that newborn larvae are extremely small and transparent, rendering them all but invisible to nocturnal predators. When artificial light interferes with established timing cues and prevents eggs from hatching, the consequences can trickle down through the food web, depriving clownfish predators of a prime energy source, and so on.

Moving forward, Fobert, Burke de Silva and co-author Steve Swearer plan on examining ALAN’s long-term effects on clownfish. The striped creatures can live for at least 30 years, making it essential to understand whether they can adapt to light over time or are simply fated to reproduce unsuccessfully in perpetuity.

“Zero percent hatching is essentially no recruiting to the next generation and could cause extinction in a species,” Thomas Davies, a conservation ecologist at Wales’ Bangor University who was not involved in the research, concludes to National Geographic. “It’s quite profound.”

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's senior associate digital editor, history.