Light pollution in the sea
Chemical pollutants, coastal zone destruction, habitat loss,
nutrient discharges, hypoxic zones, algal blooms and catastrophic
overﬁshing have all heavily impacted life in our oceans (Bowen
and Depledge, 2006). Major efforts are being made worldwide to
manage and minimise these threats. However, one particular
pollutant, light, is still permitted to ﬂood into our seas almost
unchecked. It is alarming that as the intentional and unintentional
illumination of the coastal zone and nearshore environment in-
creases unabated, we still have little idea of the extent to which
intertidal and sublittoral ecosystems are being affected. There is
also growing concern regarding the introduction of light into the
deep sea (Widder et al., 2005).
1. Sensitivity to light
Almost all living organisms are sensitive to changes in the qual-
ity and intensity of natural light in the environment (Longcore and
Rich, 2004). This is such a widely distributed characteristic that it
seems likely to have arisen very early in evolutionary history, pos-
sibly on several occasions. It might even suggest that the evolution
of life in the oceans proceeded largely in the photic zone. Obvi-
ously, for algae and seaweeds, photosynthetic activity is critically
dependent on available light, while in marine animals, tidal, daily,
monthly and seasonal cycles in natural light intensity and quality
are reﬂected in rhythmical ﬂuctuations in behaviour and physiol-
ogy that are appropriately tuned to the prevailing ecological cir-
cumstances (Depledge, 1984).
Humans use the inﬂuence of light on several kinds of organisms
to great advantage. For example, for centuries ﬁshermen have de-
ployed lanterns to attract ﬁsh to their nets, while modern day nat-
ural resource managers set out lights to attract larval ﬁsh to coral
reefs to boost ﬁsh stocks and enhance biodiversity (Munday et al.,
1998). There are numerous vivid accounts in the literature of peo-
ple using their knowledge of light-entrained rhythms to reap re-
wards. South Paciﬁc islanders for example, exploit moon phase
spawning of polychaete worms to ensure bountiful harvests of
eggs and sperm that are considered a culinary delicacy (Thorson,
2. Light pollution
Light pollution of the sea has only become a really signiﬁcant
issue over the last ca. 50–80 years. It has been deﬁned as the
‘‘degradation of the photic habitat by artiﬁcial light” (Verheijhen,
1985). Simply put, light pollution occurs when organisms are ex-
posed to light in the wrong place, at the wrong time or at the
wrong intensity. Following the mounting, well-publicised evidence
of disturbance of the behaviour of birds, bats and insects, there is
now growing concern that light pollution might exert damaging ef-
fects on aquatic species in lakes, rivers and our seas, especially in
coastal areas. All organisms equipped with an optic orientation
system are potentially susceptible. In the sea, the behaviour, repro-
duction and survival of marine invertebrates, amphibians, ﬁsh and
birds have been shown to be inﬂuenced by artiﬁcial lights (Verheij-
hen, 1985). These effects arise from changes in orientation, disori-
entation, or misorientation and attraction or repulsion from altered
light environments (Longcore and Rich, 2004; Salmon et al., 1995).
In animals exhibiting compulsive stimulus behaviour, the strength
and number of artiﬁcial lights may override any feedback control
mechanisms. This is exempliﬁed by sea turtles hatchlings that rely
on visual cues to orient themselves seaward, which consequently
renders them vulnerable to light pollution. In one anecdotal report,
500 green sea turtle hatchlings crawled to their deaths in an unat-
tended bonﬁre on a beach of Ascension Island (Mortimer, 1979).
On a Turkish beach, light pollution arising from a paper mill, a
tourist resort and a coastal village led to less than 40% of logger-
head turtle hatchlings reaching the surf (Peters and Verhoeven,
1994). The construction of buildings in close proximity to critically
important nesting beaches, as seen in the recent urban develop-
ment in Gabon’s capital, Libreville, places human populations and
their attendant light sources close to critical nesting sites for the
endangered leatherback sea turtle (Bourgeois et al., 2009). Disori-
entation and misorientation due to light pollution often divert
hatchlings along their paths to the sea leading to unnecessary en-
ergy expenditure and increased risks of dehydration and terrestrial
predation (Bourgeois et al., 2009; Verheijhen, 1985). Urban sky-
lines can present irregular silhouettes and as a result, unreliable
cues to female turtles. The confusing horizon ﬁeld presented to
new hatchlings which rely heavily on horizon elevation cues re-
sults in increased mortality (Salmon, 2006). Indirect adverse effects
of artiﬁcial lighting include a higher risk of human interference via
greater likelihood of approach towards more visible animals and of
abandonment of nesting attempts if turtles become aware of hu-
mans prior to oviposition.
Other ecological effects of light pollution include disruption of
predator–prey relationships. For example, Harbor seals (Phoca vitu-
lina) congregate to feed in illuminated areas on juvenile salmon as
they migrated downstream. Predation falls off when the lights are
turned off (Yurk and Trites, 2000). In zooplankton, vertical migra-
tions in the water column with the day–night cycle help to reduce
predation by ﬁsh and other marine organisms, when light is avail-
able (Gliwicz, 1986). Artiﬁcial light disturbs this activity. Commu-
nity changes arising from light pollution may have knock on effects
for ecosystem functions (Gliwicz, 1986, 1999). Even remote areas
can still be exposed to sky glow. Along the expanding front of
suburbanization, light may spill into wetlands and estuaries that
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are often the last open spaces in, or close to, cities (Longcore and
Perhaps surprisingly, light pollution penetrates into deep ocean
environments (Kochevar, 1998). Here, only very dim, homochro-
matic, down light is available, supplemented by bioluminescence
from marine organisms. Most inhabitants possess highly special-
ized visual systems, which are incredibly sensitive to even minute
amounts of light. This renders these organisms extremely vulnera-
ble to damage associated with bright artiﬁcial lights of manned
and unmanned submersible vehicles (Kochevar, 1998). The current
efforts to deal with the oil well disaster in the Gulf of Mexico has
revealed the extent to which light pollution can occur in the deep
sea, albeit that the effects are secondary to the effects of oil pollu-
tion in this case.
There is a widely held, but incorrect belief that organisms living
in caves (whether under the sea or under land masses) do not come
into contact with light and are therefore insensitive to it. However,
as with deep sea creatures, many cave dwelling organisms are bio-
luminescent and are exquisitely sensitive to any ambient light and
light pollution. Most if not all, cave dwelling organisms and others
living remotely from daylight, evolved from organisms that at one
time dwelt in the light and hence retain vestiges of light sensing
3. Growing concerns regarding light pollution
Over the last ca. 150 years there has been an exponential in-
crease in the use of artiﬁcial light to illuminate the night. This
trend continues to this day. On land, street lights, lighting in ofﬁce
buildings and homes, and ﬂoodlit sports facilities, industrial com-
plexes, etc., are the sources which inadvertently introduce light
into nature (RCEP, 2009). In coastal areas, where many of our major
cities such as Mumbai, Shanghai, Alexandria, Miami, New York City
and London are located, long stretches of the shoreline are strongly
illuminated. Indeed, light pollution of shallow seas has become a
global phenomenon (Elvidge et al., 1997). There are at least 3351
cities in the coastal zones around the world shedding light onto
beaches and into sublittoral areas. In Asia, 18 of the region’s 20
largest cities are located on the coast, on river banks or in deltas.
Even in Africa where the availability of electric lighting is some-
times limited, coastal light pollution is emitted from major cities
such as Abidjan, Accra, Algiers, Cape Town, Casablanca, Dakar,
Dar es Salaam, Djibouti, Durban, Freetown, Lagos, Luanda, Maputo,
Mombasa, Port Louis and Tunis (UN-HABITAT, 2009).
Our understanding of the polluting nature of artiﬁcial light is
emerging concurrently with an understanding of how patterns of
human development and economic globalization are intensifying
its impact. The UN estimates that the global population will in-
crease to a point where there are two and one half billion more hu-
man inhabitants than today (UNPOPIN). Inevitably, this growth
will be associated with further light pollution. The nature and scale
of growth provides an even louder clarion call for focus on the
environmental consequences of artiﬁcial light as well the need to
mitigate those consequences. The main conclusion to be drawn
from looking at the changing population dynamics over the next
generation is that virtually all of the two and half billion new citi-
zens of our World will live in small and medium sized cities within
emerging economies (Balk et al., 2008). Thus, while mega-cities
continue in their dominant position, more modest sized cities will
serve as the true future centres of growth. This means that artiﬁcial
light will not only continue to intensify with population growth,
but that the number of locations of high intensity light pollution
will also increase dramatically. Even in areas where total popula-
tion growth is low, such as in the OECD countries, analysis suggests
that the environmental inﬂuences of night light will continue to
spread. Consideration of data provided by the US National Geo-
physical Data Center (NOAA), reveals that total population growth
and the spatial patterns of human growth can be, and often are,
unrelated (Bowen et al., 2006; FAO, 2005). Migration to the coast,
so common in many parts of the world, and the ‘‘sprawl” of devel-
opment, present a challenge regardless of total population growth
While most of the future increase in artiﬁcial light will reside
with permanent resident populations, economic globalization will
also play a role. In 2009, the UN World Tourism Organization
(UNWTO) estimated that there were nearly 900 million interna-
tional tourist arrivals worldwide. The economic growth and devel-
opment pressure (very often coastal) of new supporting
infrastructure, driven by international tourism, cannot be ignored.
Indeed, touristic development may be a disproportionately impor-
tant driver of artiﬁcial light use simply because it tends to occur in
areas of enhanced natural beauty – and environmental vulnerabil-
ity. In other words, wherever tourism increases, so too does light
Holiday visits to beaches vividly reveal the extent to which arti-
ﬁcial lighting systems have been deployed along coastlines. More
systematic studies demonstrate the extent of the change that has
occurred. Innovative research using satellite imagery has tracked
the movement of populations over time. This is based on the prin-
ciple that wherever human population density increases it is
almost always associated with increased use of artiﬁcial light at
night. From a comparison of images taken at various times over
the past 50 years with present day images, it is clear that not only
has population density increased in many coastal areas around the
World, but this is associated with dramatic increases in light inten-
sity in the coastal zone.
4. What can be done?
From a mitigatory/regulatory perspective the above mentioned
patterns of human population change may provide vehicles to
more efﬁciently limit future environmental damage associated
with artiﬁcial light. If intensifying urbanization is effectively antic-
ipated and understood, it might be easier to coordinate regulatory
responses and technological efﬁciencies of scale. Thus, if most of
the future growth is geographically concentrated, the ability to
coordinate light pollution control measures could be enhanced.
The same might be said of touristic development. It provides a
commonality of activity that can be dealt with by a more concerted
and directed response.
In all other spheres of activity that result in artiﬁcial light
impacting marine life, there are clearly possibilities to regulate
light spillage into the sea. Whether from coastal developments or
ﬁshing, or from oil and mining exploration or from cruise liners
and other merchant shipping activities, there are a wide range of
opportunities to regulate and thereby minimise potential adverse
effects of light pollution. Simply embedding the idea that in every-
thing we do, consideration needs to be given to minimising the
amount of light we release into the environment, would be a help-
ful step forward.
Whatever is done, it is ﬁrst and foremost essential to recognize
the scale and scope of the potential problem in hand. It is almost
unimaginable that if we discovered a new pollutant today that
had pronounced effects on fundamental cellular processes, that af-
fected biological rhythms of cells, and that potentially affect photo-
synthesis, that we would not control or regulate its release into
natural ecosystems! Yet this is precisely what we do when we
allow light to spill into our seas, estuaries, rivers and lakes, as well
as into terrestrial ecosystems. The evidence is clear that the
1384 Editorial / Marine Pollution Bulletin 60 (2010) 1383–1385
feeding, reproductive and migratory behaviour of some species is
already affected. It seems timely therefore to reconsider our prof-
ligate use of light and to pay more attention to its biological effects.
If nothing else, more prudent use of artiﬁcial light would also re-
duced energy consumption and related greenhouse gas emissions,
surely a worthy goal in itself?
We gratefully acknowledge the support of the UK Government
Foreign and Commonwealth Ofﬁce and of the Peninsula Founda-
tion, UK, for providing ﬁnancial support to facilitate collaboration
among the authors.
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Michael H. Depledge
European Centre for Environment and Human Health,
Peninsula Medical School,
Universities of Exeter and Plymouth,
Truro, TR1 3HD, UK
E-mail address: email@example.com
Céline A.J. Godard-Codding
Department of Environmental Toxicology,
The Institute of Environmental and Human Health,
Texas Tech University,
Lubbock, TX 79409, USA
Robert E. Bowen
Environmental, Coastal and Ocean Sciences,
University of Massachussetts,
Boston, MA, USA
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