Oceanography | September 2020
state the biologists in Global Change
Biology. The work lends yet more cre-
dence to the emerging threat of light pol-
lution and its impacts on the biology of
corals, says Levy, “and will help in find-
ing ways of mitigating potentially harmful
effects. Reducing the exposure of corals
to artificial light at night could help protect
and regenerate coral reefs.”
CORAL REEF CLOWNFISH
THREATENED BY ARTIFICIAL
LIGHT AT NIGHT
The light-hearted movie Finding Nemo
could soon have a much darker sequel.
Artificial light at night in coral reefs leaves
the famous reef clownfish unable to pro-
duce offspring.
Studies by scientists at Australia’s
Flinders University and the University
of
Melbourne
published
in
Biology
Letters show that an increasing amount
of artificial light at night in coral reefs,
even at relatively low levels, masks nat-
ural cues that trigger clownfish eggs to
hatch after dusk.
Lead author Emily Fobert of the
University of Melbourne says that eggs
incubated in the presence of artificial light
had a zero hatching success rate.
“The overwhelming finding is that arti-
ficial light pollution can have a devastat-
ing effect on the reproductive success of
coral reef fish,” says Fobert. “When ALAN
was present, no eggs hatched but when
the light was removed during the recov-
ery period, eggs from the ALAN exposure
hatched normally. The presence of light is
clearly interfering with an environmental
cue that initiates hatching in clownfish.”
Fobert monitored 10 breeding pairs of
clownfish exposed to an overhead LED
that imitated commercially available and
widely used lights.
The results indicate that increasing
amounts of light at night can significantly
reduce reproduction in reef fish. “These
findings likely extend to other reef fish as
many share similar reproductive behav-
iors, including the timing of hatching
during early evening,” says Fobert.
Some tropical tourist hotspots include
floating accommodations above coral
reefs. Many overwater bungalows have
glass floors with lights shining directly
onto reefs below so guests can watch
fish at night.
Coauthor Stephen Swearer of the Uni-
versity of Melbourne says that clownfish,
along with many other fish species that lay
eggs on coral reefs, are at particular risk
because their larvae usually hatch a few
hours after dusk. “The presence of ALAN
could compromise their natural spawning
rhythms,” he says.
Karen Burke da Silva of Flinders
University, also a coauthor, believes
that an improved understanding of the
impacts of ALAN on coral reefs can lead
to solutions for these stressed ecosys-
tems. “Artificial light at night is becoming
a greater concern among ecologists. Light
is increasing globally and the impacts on
organisms can be severe, but very little
research has been done on ALAN in the
marine environment.”
If we don’t find ways of decreasing artifi-
cial light at night, “Nemo” and his kin may
be among the last clownfish on the reef.
Whither go the clownfish, the rest of the
coral ecosystem may soon follow.
It’s high time, researchers say, to turn off
the lights.
ABOUT THE AUTHOR
Cheryl Lyn Dybas (cheryl.lyn.dybas@gmail.com), a
Fellow of the International League of Conservation
Writers, is a contributing writer for Oceanography
and a marine ecologist. She also writes about sci-
ence and the environment for National Geographic,
BioScience, National Wildlife, Ocean Geographic,
Canadian Geographic, and many other publications.
Researchers are studying the effect of artificial light at
night on reef clownfish reproduction. Credit: University
of Melbourne/Flinders University
Oceanography | September 2020