Finding Nemo has a great role of introducing the bright orange clownfish to the world. On one hand, it’s good since everybody knows about this species, but on the other hand, there are problems that they face in the wild.
Clownfish gets overharvested due to market demand (more people want them inside their aquarium). And not just that, their coral and anemone homes get bleached because of climate change-induced warming waters. Sadly, this species has got one more problem, which is light pollution.
Biology Letters stated that a new study revealed that clownfish, which are dependent on coral reefs, can’t raise any young when exposed to artificial light.
We all need lights that’s for sure, but the human-made ones prove to be problematic towards animals across ecosystems. Nighttime lights alter birds’ nocturnal migrations. Plants bloom earlier. Sea turtles avoid nesting on brightly-lit beaches. Songbirds start warbling earlier.
It turns out, aquatic life gets negative impacts as well. Emily Fobert, a marine ecologist at Flinders University in Australia and lead author of the study, said, “We don’t think about underwater marine systems being potentially impacted.”
Thomas Davies, a conservation ecologist from Bangor University in Wales, added, “I wasn’t expecting the result [in the paper] to be that nothing hatched. It’s quite worrying…a really big result that speaks to how light pollution can have a really big impact on marine species.”
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In the study, Fobert and her team observed 10 pairs of clownfish in a lab—each clownfish pair had their own aquarium. Half of the tanks experienced typical light as they would on a natural coral reef—12 hours of light and 12 hours of darkness. But the other half experienced a low level of artificial light at night, mimicking light pollution from an average coastal town.
For around 2 months, researchers counted how often the fish spawned, how many eggs were fertilized, and how many eggs hatched. No fish hatched when there was artificial light. The clownfish exposed to artificial light at night still spawned, and the eggs were still fertilized at a similar level as the normal fish. But there was no hatching.
But as soon as researchers removed the light at night, hatching resumed and jumped back to match the hatching rate of the normal fish.
Clownfish eggs change into a silvery color before they hatch. All eggs turned shiny, and the eggs which were under a normal light-dark cycle hatched. Researchers watched for several days as the eggs exposed to light at night didn’t hatch. The silver color disappeared, and the egg turned opaque.
Karen Burke da Silva, a co-author at Flinders University, clownfish expert, and director of the organization Saving Nemo, said that it’s sad to know that all efforts done by those clownfish were futile. “Parents were awake longer at night and they were taking enormous care of these big beautiful embryos,” said Burke da Silva.
Smaller males care for the eggs, fanning them and mouthing them to clean them. Because reproduction for these fish is incredibly energetically costly, said Fobert, there could be consequences that have yet to be measured.
Stephen Swearer, a marine biologist at the University of Melbourne in Australia and co-author of the study, said although they didn’t see a drop in spawning and fertilization rates in the study, higher light levels could cause a bigger impact.
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Lights out, less dangerous
Artificial light comes from any developed area: houses, streetlights, hotels, and offices. Almost 80% of people worldwide live in areas with light pollution. And now more people use cheaper, more energy efficient LED lights.
LED lights are economically beneficial to us humans and somehow they help the environment. However, they emit more light at shorter wavelengths, blue light. In humans, blue light might not have positive health effects. This light disrupts sleep by interrupting normal cycling of the hormone melatonin. Fobert said that this blue light penetrates more deeply into the water and can disrupt natural systems most.
Animals have evolved their internal clocks. They know when to feed and have babies, or when to sleep based off night and day timing. Exposure to light during a period that is supposed to be dark confuses biological rhythms.
For clownfish babies, the beginning of darkness triggers their eggs to hatch during a safer period to avoid predators. Fobert speculated that exposure to light during critical hours after dusk most likely causes this reduction in hatching. If it were dark during key hours, the eggs might still hatch.
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What will become of clownfish?
In the wild, clownfish use anemones for their individual love shacks, with one pair per anemone. And most clownfish live in shallower water, within 9 meters from the water surface. Fish that live in deeper water won’t be impacted by light as much but light will definitely reach fish like clownfish.
Clownfish that live at shallow depths could be in trouble. Finding a new anemone with less light would be difficult because good anemones are already taken. Taking over them is quite impossible since clownfish are territorial and guard their homes fiercely. An open anemone farther away might attract them, but clownfish are poor swimmers, so moving away isn’t a good option.
“Artificial light can have impacts with severe consequences for populations. Zero percent hatching is essentially no recruiting to the next generation and could cause extinction in a species. It’s quite profound,” said Davies.
Although, not all hope is lost. Researchers ran the experiment for several months, so this study is only peeking into the possible effects from light pollution. “The research is really exciting, but it just opens up so many more questions. We are just scraping the surface,” said Fobert.
Stephen Swearer, a marine biologist at University of Melbourne in Australia and co-author of the study said that the next steps are looking at how light pollution affects clownfish in the long term. Since clownfish can live for at least 30 years, it will be important to understand if the fish can adapt to light, or if they can’t have any babies during their whole lifespan.
“While it’s depressing, there is still hope,” said Damon Bolton, a marine ecologist at University of New South Wales in Australia. Hopefully humanity can come up with a type of light that’s not only beneficial to humans and the environment but also the aquatic life.
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