Light pollution has intensified in the past half-century with increasing population and industrialisation. In disrupting ecosystems, it poses a serious threat to nocturnal wildlife, having negative impacts on plant and animal physiology. It can confuse the migratory patterns of animals, alter competitive interactions of animals, change predator-prey relations, and cause physiological harm. Knappily analyzes this often ignored form of pollution with new research indicating its effects even on coastal ecosystems.
What is light pollution?
Light pollution, also known as photopollution, is excessive, misdirected or obtrusive artificial light. As a major side-effect of urbanization, it is blamed for compromising health, disrupting ecosystems and spoiling aesthetic environments.
- Light pollution is a side effect of industrial civilization. Its sources include building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues.
Scientists have recognised for some years that light pollution impacts the behaviour and success of many animals including migrating birds, hunting bats and the moths they try to capture.
- All animals and plants on this planet (including humans) are genetically adapted to regular day/night/seasonal cycles that have, in many places on the planet, been completely interrupted by the glow created by artificial lights.
- Although some animals may capitalize on the lighting, many suffer its effects, and one hundred years is not enough time to genetically adapt to these changes.
To understand the effects of artificial light, we must first understand the difference between diurnal and nocturnal creatures.
- Diurnal species are species that are primarily awake during the day, and sleep at night. These include animals such as bees, squirrels, songbirds, and even humans.
- Nocturnal animals sleep during the day, and move about at night. These include animals such as moths, bats, frogs, and cats. Artificial light affects both, but in different ways.
Artificial light has several general effects on wildlife:
- Attracts some organisms (moths, frogs, sea turtles), resulting in them not being where they should be, concentrating them as a food source to be preyed upon, or just resulting in a trap which exhausts and kills them.
- Repels some organisms, excluding them from habitat where they might otherwise make a living. Makes it a form of habitat loss.
- Alters the day/night patterns, resulting in not getting enough sleep, not having enough down time for the body to repair itself, alters reproductive cycles.
Humans can go inside and turn out the lights out to prevent these issues, but the frogs in the pond by the streetlamp can’t. For animals that are very site specific, it’s not an option to move. They just get eaten, or fail to reproduce. For those that can move, as more and more lighting encroaches on dark areas, the areas that are dark enough to move to become fewer and further between. Artificial lighting is another form of habitat loss.
Why is it a growing concern?
The effects of night lighting on wildlife have been known for hundreds, even thousands, of years. Hunters and fishers have used torches, lamps, and other light sources to attract their quarry to them, so powerful is the effect of light on some species.
- Gas-lit lighthouses have long had the reputation of attracting marine birds by the thousands, as well. But only in the past century, with the advent and spread of electricity, has the problem of artificial night lighting become so pervasive.
- Light pollution has intensified in the past half-century, increasing about 6% each year in North America and Europe, according to a research published along with an atlas of worldwide light pollution by researchers of Light Pollution Science and Technology Institute in Thiene, Italy.
As the human population grows the problem is due to worsen and even remote coastal areas are now being affected by civilization’s tell-tale glow-in-the-sky. Turtles, disoriented as they return to their nesting beaches, or confused hatchlings struggling to find the sea, are iconic examples.
Case-in-point: The turtles of Israel
- Light pollution along the Mediterranean is changing the nesting habits of sea turtles in Israel, according to new research. Orbital pictures of the region, coupled with sea turtle nesting data from Israel’s National Parks Authority, revealed that the species of turtles in that area cluster their nests in darker spots.
- “The two species of sea turtle in our study are nocturnal nesters. It is thought that the light pollution along the coast at night could disrupt visual cues. Visual cues are important for sea turtles for other functions, such as finding the sea after nesting or hatching,” lead researcher Tessa Mazor told LiveScience.
When did research show the effect of light pollution on coastal species?
Approximately 22% of coastlines around the world experience artificial light at night, yet little research has been conducted on these intertidal ecosystems. To address this, a collaboration between the University of Exeter and the Plymouth Marine Laboratory conducted a series of experiments to determine whether a key intertidal species was affected by exposure to night-time lighting. The study looks at the true extent to which light pollution is affecting key marine wildlife in the UK.
- Using the dogwhelk (Nucella lapillus), a key seashore species that modulates biodiversity and community structure of our coasts, they kept one group of dogwhelks in artificially-lit night sky conditions, while a control group experienced a more natural night/day cycle.
- The research showed that those dogwhelks kept under artificial lighting conditions were less likely to seek out shelter and spent longer seeking food — putting them at exposed risk to predators and placing them in more stressful conditions.
The study showed, for the first time, that night time light changes species interactions at the heart of the way in which natural food chains work, raising concern about how generalised these impacts may be for natural marine wildlife.
- Dogwhelks are far from unimportant along rocky coasts, where they can occur in dense aggregations, and play a key role in the ecological balance, feeding on barnacles, limpets and mussels.
- Disturbing these balances can have major ramifications across habitats and up food webs.
Dr Thomas Davies from the University of Exeter highlighted how historically overlooked the impacts of light pollution on coastal ecosystems has been, saying: “There has been a surge of research into the impacts of artificial lighting on land animals and plants over the last six years, but the influence on coastal animals of lights from harbours, marinas, piers and promenades has received very little attention. Understanding how to manage ecosystems to improve biodiversity gains is as important in the built marine environment as it is in our city parks, gardens, streets, rivers and canals. This study highlights that night-time lighting in coastal cities can impact biodiversity on rocky shores popular with beachgoers that enjoy the diversity of life they offer year round.”
Where are the areas its impact is seen most?
It is most severe in highly industrialized, densely populated areas of North America, Europe, and Japan and in major cities in the Middle East and North Africa like Tehran and Cairo, but even relatively small amounts of light can be noticed and create problems.
- The new atlas by Light Pollution Science and Technology Institute in Thiene, Italy, shows that now, more than 80% of humanity experiences light-polluted night skies, which includes roughly 83% of Earth’s population, and more than 99% of Europeans and Americans.
- By population, Singapore has the world’s most light-polluted skies, followed by Kuwait, Qatar, and the United Arab Emirates — all densely populated countries. Africa has the dimmest skies; the top 10 least polluted countries are on the continent.
Europe has some of the worst light pollution on the planet. In fact, almost the entire continent is bathed in an uninterrupted nighttime skyglow.
- The heaviest light pollution occurs along the border of Germany, Belgium and the Netherlands, especially around Amsterdam.
- Industrial areas of England are also seriously affected. A near-continuous region of heavy light pollution extends from Liverpool and Manchester, down through Birmingham to London.
And much of North America is bathed in skyglow too, particularly the eastern United States.
- The country’s worst light pollution occurs over an uninterrupted urban area that stretches from Washington D.C., through Baltimore, Philadelphia, and New York, and all the way up to Boston.
- Major metropolitan areas around San Francisco and Los Angeles are also bathed in intense light pollution.
Southern and eastern Asia appear to suffer less from light pollution than other areas, though Hong Kong and Shanghai — as well as the major cities of South Korea — don’t escape the glow of artificial lighting.
- North Korea turns off most of its lights during the evening, so it’s pitch-black on the map — proving experts’ argument that turning off lights is one of the most effective ways to reduce light pollution. There is something to learn from North Korea after all.
Who are the worst affected?
- Most people are familiar with the saying, “Like a moth to the flame.” Artificial lighting is extremely detrimental to many insect populations, acting like a vacuum that they cannot escape.
- Even one artificial light source can disrupt normal flight activity, long distance migrations, or even attract insects that don’t normally move from their habitat.
- Once the insects are effectively trapped by the light, they can be killed directly by lamp’s heat, they may circle the light until caught by predators, or they may stop to rest on the ground under the light, where they are also preyed upon.
- Distant sky glow may also disrupt their migrations, but no data are available about this potential effect.
- Light traps are very likely changing the diversity of insects; for instance, in one study, scientists collected 50,000 moths in a single night. If a particular species does not reproduce rapidly enough to make up for the loss at the lights, it may disappear from the community.
- For insects that are important as pollinators, or predators of nuisance insects, their loss is detrimental to human communities as well.
- Sea turtles are the most well-known species of reptiles that are negatively affected by artificial light. Female turtles nest on subtropical and tropical beaches around the world. About two months later, the hatchlings burst from the nest en masse and start scrambling to the brightest horizon. On a natural beach, this is toward the moon and starlight glimmering off the water, and away from the shadowy dune.
- Artificial lights cause a problem for hatchlings because they lead the small turtles away from the safety of the water, where they succumb to dehydration, predators, or even being run over by cars.
- They also affect nesting females, who may spend valuable energy moving toward lights and away from the water instead of returning to the sea after nesting.
- Tragically, nesting females may also be attracted to roads where they are hit by cars. The loss of a female who has, against the odds, made it to reproductive age is a significant loss to these threatened and endangered populations.
- Other species of reptiles are also affected by artificial light. For example, geckos are a nocturnal species of reptile that are drawn to light to feed. This, in turn, makes the geckos more susceptible to predators.
- The effect of artificial lights on birds has been known for centuries. In the past, people used flame and lights to attract birds at night to capture them for food. Since their inception, there have been reports of seabirds attracted to the light beam of lighthouses.
- Artificial lights can “trap” migratory birds by bleaching their visual pigments, causing them to lose sight of the horizon and circle within the cone of light endlessly. They then can die from exhaustion or collision with the light source.
- It can extend the day for diurnal species of songbirds, making them more susceptible to predators as they sing out their location, or causing them to breed too early since they associate breeding with longer days.
- It can attract seabirds away from their normal feeding grounds, possibly because these birds feed on bioluminescent sea animals and are cued in to low levels of light.
- Most mammals, humans may find it difficult to believe, are nocturnal. Studies have found that many small mammals (for example, mice) eat less food in areas that are lit by artificial light, assumedly to avoid predators. Conversely, other studies have found that predators of small mammals (for example, foxes), are attracted to lit areas, possibly for easy prey.
- Artificial light has also been shown to affect the circadian rhythm of some mammals including humans, extending the day of diurnal species, and shortening the day of some nocturnal species. In rats, artificial light at night suppressed melatonin production, and resulted in an increased rate of tumors.
- Bats are well known to be affected by artificial lights. Many species of bats use artificially lit areas as an easy foraging ground, which can affect the local population of insects. Some bats, however, avoid the lit areas, and are then outcompeted by the bats that get increased food from the lit areas.
How can this problem be solved?
Plymouth Marine Laboratory senior ecologist Dr Ana Queirós says: “Unlike for climate change, the solution for night time light pollution is well within our reach, as restricting use of lights to specific colours can much limit their negative impacts on wildlife, as has been shown in terrestrial studies. We should be acting on coastal light pollution immediately, because this time, we can actually fix the problem.”
- Keeping the light low (mounting the fixture as low as possible) and shielded (fully shielding the light so bulbs and/or glowing lenses are not visible) cuts down on the amount of glare and light visible to the animals, so that there is less opportunity for them to get trapped, repelled, or have their day/night patterns altered.
- Keeping it long wavelength (ambers and reds) actually makes the light that is visible seem dimmer to nocturnal animals that primarily use rod vision. The rod system’s peak sensitivity is at 496 nm, so a low pressure sodium light, with its emitted light at 589 nm, should seem 1/10th as bright to an animal using purely rod vision vs. an animal that uses rods and cones to see.
Changing to low, shielded, and long wavelength lights also results in energy savings.
- For instance, lights that are lower and shielded often result in more lumens (light) being focused onto the ground, rather than wasted illuminating the sky above the light.
- Additionally, some long wavelength light sources such as low pressure sodium lights and amber LEDs use a fraction of the energy of their mercury halide, incandescent and even fluorescent counterparts.
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