Night lights: New global atlas maps out artificial light at night under
the sea

Date:
December 14, 2021
Source:
University of Plymouth
Summary:
A new study maps out areas of the ocean most affected by light
pollution, and shows that up to 1.9 million km2 of the world's
coastal waters are being exposed to biologically significant levels
of artificial light at night.



FULL STORY ==========================================================================
As coastal areas become increasingly developed, concerns are growing about levels of artificial light at night (ALAN) and its potential impacts on
the marine environment.


========================================================================== Light pollution is well studied in terms of its effects on the night sky
and astronomy, and on terrestrial ecosystems, but until now researchers
didn't know the full extent of ALAN in the oceans.

A new study, funded by the Natural Environment Research Council, maps
out areas of the ocean most affected by light pollution, finding that
up to 1.9 million km2 of the world's coastal waters are being exposed
to biologically significant levels of ALAN.

The study brought together researchers from the University of Plymouth, Plymouth Marine Laboratory, University of Strathclyde, The Arctic
University of Norway, Bar-Ilan University, The Interuniversity Institute
for Marine Sciences of Eilat and Beit Berl Academic College.

By combining various techniques including computer modelling, satellite technology and in situ observations in the River Tamar with a pre-existing world atlas of artificial night sky brightness, the researchers were able
to build up a picture of the coastal ocean areas being exposed to ALAN.

In order to gauge artificial light in marine systems, the study used
the light sensitivity of copepods (a type of microscopic crustacean)
as a metric to determine the depth of light penetration.



========================================================================== Setting light levels by how detectable they are to marine organisms is
key, considering the possible impacts of ALAN pollution on the creatures
that live in the sea.

Many marine species are accustomed to the predictable light changes
that occur naturally throughout the day, across seasons and with the
lunar cycle.

However, light from coastal developments can scatter a long way out
to sea and is spectrally quite different to moon and sunlight. It also
differs in the wavelengths penetrating the water column.

The new global atlas of ALAN under the sea shows that at a depth of
one metre, 1.9 million km2 of coastal ocean are exposed to biologically important ALAN (around 3.1% of the global Exclusive Economic Zones). At
10m deep, 1.6 million km2 is exposed (2.7%) and by 20m down, 840,000 km2 (1.4%).

Dr Tim Smyth, PML Head of Science for Marine Biogeochemistry and
Observations and lead author on the research, added: "Creating this atlas
shows us how widespread the issue of artificial light at night is in our coastal seas and could hopefully lead to highlighting ALAN as a descriptor
of disturbance in the same way we currently look at underwater noise as
a concern. There's still a lot of investigation needed to understand
the specific effects on marine organisms, the exact spectral nature
of this light pollution and how it is changed by seasons or tides,
for example. But recognising its global presence in this way is a major
step forwards in understanding ALAN and its consequences for the ocean."
Dr Thomas Davies, Lecturer in Marine Conservation at the University of
Plymouth and the study's senior author, said: "The extent of artificial
light pollution on land has been known for many years now. Some people
might consider that this light does not enter the Oceans, but it does, and
in sufficient quantities to cause biological impacts. This atlas is the
first to quantify the extent of ALAN in the Oceans. The severity of the
problem in certain regions including the Mediterranean, Persian Gulf and
South China Sea is really quite alarming." The study is part of ongoing research into the effects of artificial light on the marine environment, conducted as part of the Artificial Light Impacts on Coastal Ecosystems
(ALICE) project.

In a study published in Scientific Reports in July 2020, the same team
showed that coastal cities leave up to 75% of their neighbouring seafloor exposed to harmful light pollution.

Research published in Current Biology in June 2020 also demonstrated
that artificial lighting along the world's coastlines could be having
a significant impact on species that rely on the moon and stars to
find food.

========================================================================== Story Source: Materials provided by University_of_Plymouth. Original
written by Alan Williams. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. T. J. Smyth, A. E. Wright, D. McKee, S. Tidau, R. Tamir,
Z. Dubinsky, D.

Iluz, T. W. Davies. A global atlas of artificial light at night
under the sea. Elementa: Science of the Anthropocene, 2021; 9 (1)
DOI: 10.1525/ elementa.2021.00049 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211214152147.htm

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