First person: Why clownfish need darknessPlay
Listen to our hour In defense of darkness.
Emily Fobert is a research fellow at the University of Melbourne in Australia. In the lab, Emily studies how light pollution affects marine life.
MEGHNA CHAKRABARTI: Emily Fobert is a research fellow at the University of Melbourne in Australia, and she studies how humans impact underwater ecosystems, especially when it comes to artificial light. And her work was inspired by a research trip she took in 2017.
EMILY FOBERT: I went to French Polynesia with a colleague. And it's a relatively remote island, but there's all these hotels with overwater bungalows and lights shining right down on the reef. Some of them even have, you know, the glass floors and the bungalows with the lights directed on to the reef below. The tourists can look at the fish at night. And, you know, I've heard that there's impacts of light pollution on a lot of terrestrial animals and humans, for sure.
So just seeing all that light pollution in the marine environment made me realize that it's something we haven't been looking at, but it's probably an issue there as well.
CHAKRABARTI: So back at the lab, Emily decided to see whether light pollution had an impact on a specific underwater species Clownfish. There was orange and white fish that make their homes in anatomies on coral reefs.
FOBERT: So I had a bunch of clownfish in the lab and breeding pairs, so a female and a male each in their own aquarium kept track of how many eggs they're laying, how frequently they were laying them. And then I put lights on half of them. So half of them were mind control. So they still experience 12 hours of daylight and 12 hours of complete darkness. And then the other half had 12 hours of daylight and 12 hours where they are exposed to a dim light at night.
And that's kind of equivalent to what you might expect from a source of lights on marine infrastructure. So on a pier or over a water hotel that might have lights on it shining downwards. And then I monitored how many of the eggs actually hatched in both the control and the light conditions. So what I found is when the fish had 12 hours of daylight and 12 hours of darkness at night, we had about 80% match success. So 80% of the eggs crashed. It's pretty normal to have high mortality in early life stages of fish because they have thousands of eggs.
But then when I put the lights on at night so that when they're exposed to low levels of light at night, 0% of the eggs hatched. So none of them hatched. Pretty stark results. So I removed the lights and I continued to monitor them for another couple months. And essentially, as soon as I remove the lights, the next batch of eggs from the same cache would hatch. So 80% hunch rate again.
So it was very clearly the light that was inhibiting that hatching process. A lot of coral reef fish eggs actually hatch a couple hours after sunset. Translucent larvae are not very visible at night. There's not as many predators around. So they hatch, they get off the reef really quickly in the cover of darkness. Clownfish. Most fish. Most organisms on earth meet darkness for various reasons. But there's still not a ton of research done on light pollution in the marine environment.
So, yeah, there's a lot of questions still out there, but no doubt that animals need darkness. Whenever anyone asks me what I do and I, I mention, you know, like pollution, fish. There's like, what? Light pollution underwater. Really? Like, people don't get that, you know, light travels through water still. And everything that we do on land on the coast, that's that's impacting everything underwater.