Oceanography | September 2020
Satellite view of artificial light
at night. Credit: NASA
TURN OFF
THE LIGHTS
Satellite images of Earth at night: bright
dots and shining webs that tell the story of
humans’ seemingly endless sprawl across
the globe.
Artificial “sky glow” can now be detected
along 22% of the world’s shorelines. That
figure is expected to increase dramatically
as human populations along coasts more
than double by 2060.
All that light has a downside. Concerns
have recently bubbled up about the dam-
aging effect of artificial light at night, also
known as ALAN, on humans and other spe-
cies. At the top of the list are coral reefs.
Artificial light at night and how it affects
corals is the subject of new research by
scientists at several institutions, including
the University of Southampton in the UK.
With funding from the UK Natural Envi-
ronment Research Council, Southampton
scientists Jörg Wiedenmann and Cecilia
D’Angelo of the university’s Coral Reef
Laboratory are tackling gaps in our under-
standing of how ALAN affects the repro-
duction of reef corals.
They are working with a team at Bangor
University and other UK research institu-
tions, the Interuniversity Institute for Marine
Sciences in Eilat, Israel, and the Horniman
Museum in London. The research is part of
a larger project led by University of Bangor
scientists studying the impacts of artificial
light at night on marine life.
“ALAN represents an emerging threat
that has received little attention in the
context of coral reefs, despite the poten-
tial of disrupting the chronobiology, phys-
iology, behavior, and other biological
processes of coral reef organisms,” write
Inbal Ayalon and Oren Levy of Bar-Ilan
University and their colleagues in a 2019
paper in Global Change Biology.
Coral reefs are in decline as a result
of climate change, coastal construction,
overfishing, pollution, and nutrient enrich-
ment, says Wiedenmann. “The key to
coral reef survival is for the remaining indi-
viduals to produce enough offspring that
can survive on damaged reefs and help
the reefs recover.”
ALAN, however, presents a major road-
block.
To maximize reproductive success, many
corals release their eggs and sperm at the
same time, sometimes on only a single
night of the year in a process called mass
coral spawning. The timing of spawning is
thought to be synchronized with and trig-
gered by the light of the moon. Scientists
fear that increasing levels of artificial light
at night may override age-old signals from
moonlight, resulting in less efficient coral
reproduction and reduced recruitment of
juvenile corals.
Coastlines are exposed to artificial light
at night near piers, promenades, ports,
harbors, and dockyards. They’re increas-
ingly illuminated with LED lighting, which
penetrates deeper into seawater than
older lighting technologies. LED lighting is
predicted to make up 69% of global light-
ing by the end of this year, exacerbating
ALAN’s effects.
The presence of artificial light in coastal
regions has the potential to interfere with
natural light cycles, ultimately reshap-
ing the ecology of coastal habitats, says
Wiedenmann. “We know that many
marine invertebrates are extremely sen-
sitive to natural light throughout their life
cycles, and that gradients of light intensity
and color, largely caused by variations in
moonlight and sunlight, are major factors
in marine ecosystems.”
Artificial Light at Night, a New
Threat to Beleaguered Coral Reefs
By Cheryl Lyn Dybas
Oceanography | September 2020
RIPPLE MARKS: THE STORY BEHIND THE STORY