Losing Nemo? Nighttime Light Pollution Can Stop Clownfish From Hatching, Study Shows
Light pollution is increasing near coral reefs as coastal developments expand. Some bungalows are even built above the reef with clear floors, so that tourists can watch the fish at night. But that means the fish can see the light from the bungalows, too.
A group of Australian researchers set out to investigate how that light might impact one of reef's most iconic residents: the clownfish. Their results were dramatic: When clownfish eggs were exposed to artificial light at night (ALAN), not a single one hatched.
"The overwhelming finding is that artificial light pollution can have a devastating effect on reproductive success of coral reef fish," lead study author and Flinders University Research Associate Dr. Emily Fobert said in an email to EcoWatch.
Excited to share our new paper out in Biology Letters today, showing artificial light at night causes reproductive… https://t.co/KjLToe91O0— Dr Emily Fobert (@Dr Emily Fobert)1562752065.0
The results, published in Biology Letters Wednesday, show that the fish are very sensitive to even low levels of artificial light.
"When ALAN is present, no eggs hatched but when the light was removed during the recovery period, eggs from the ALAN exposure hatched like normal, so the presence of light is clearly interfering with an environmental cue that initiates hatching in clownfish," Fobert said.
To achieve their results, Fobert and her team examined 10 pairs of common clownfish (Amphiprion ocellaris) in a lab, as National Geographic explained. Each pair had its own tank. Half of the tanks were lit like a natural coral reef: light for 12 hours and dark for 12 hours. The other half were exposed to nighttime light levels similar to those a typical coastal town would emit. The researchers then studied the fish for 60 days to determine how the differing light levels impacted spawning, egg fertilization and egg hatching. They found no change to spawning or fertilization, but a surprisingly extreme change to hatching.
"I wasn't expecting the result [in the paper] to be that nothing hatched," Thomas Davies, a Bangor University in Wales conservation ecologist, told National Geographic. "It's quite worrying … a really big result that speaks to how light pollution can have a really big impact on marine species."
Clownfish are so sensitive to light because they spawn around the full moon and their eggs typically hatch after sunset, according to a Flinders University press release. The nighttime hatching likely keeps the new babies safe from predators, National Geographic explained.
"These findings likely extend to other reef fish as many share similar reproductive behaviors, including the timing of hatching during early evening," Fobert said in the release.
Davies thought the study's implications for clownfish could be severe.
"Zero percent hatching is essentially no recruiting to the next generation and could cause extinction in a species. It's quite profound," he told National Geographic.
The paper authors wrote that more work needed to be done to see how light levels might impact clownfish in the wild, but ALAN is a growing concern. A 2017 study found that the earth area lit by artificial light at night grew by around 2 percent per year from 2012 to 2016.
Senior author, founder of the conservation group Saving Nemo and Flinders Prof. Karen Burke da Silva explained that the clownfish study began to fill an important knowledge gap.
"Artificial light at night is becoming a greater concern among ecologists, as light is spreading globally, and the impacts on organisms can be severe, but very little research has been done around ALAN in the marine environment," she said in the press release.
Correction: A previous version of this article said that 10 clownfish were used in the experiment. It has been corrected to reflect the fact that 10 pairs were used.
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By Katherine Kornei
Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:firstname.lastname@example.org" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
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