Coastal tourism contributes to local economies, generates employment, and strengthens communities but it comes with a cost. As development and consumption become more demanding in communities surrounding coastal areas, it causes loss of natural and semi-natural land. To construct more open beaches, habitats like seagrass meadows and mangrove forests have been destroyed. A range of tourism activities have also, directly and indirectly, caused coral bleaching and have interrupted the organic growth of dolphins, among others.
Coastal light pollution in the seafloor
On top of these negative impacts on coastal development, a new study reveals that coastal cities expose up to 76% of marine ecosystems to nighttime light pollution.
The study led by the University of Plymouth showed that under both clear and cloudy skies, the amount of light used in everyday street lighting in coastal areas permeated all areas of the sea nearby. Such artificial lighting could pose a significant threat to coastal species. Exposure to red wavelengths may be nominal but exposure to green wavelengths was the highest, the authors said.
Artificial light at night (ALAN)
Artificial light at night (ALAN) has been increasingly recognized to disrupt the natural patterns of light both through skyglow and direct effects of illumination from light sources. Thomas W. Davies from the School of Biological and Marine Sciences of the University of Plymouth and the team wrote that ALAN can be detected above 22% of the global coasts nightly and is expected to increase as the coastal human populations are projected to double by 2060.
Considering the low levels of ALAN reaching the seafloor, it seems intuitive to say that light pollution is not a concern in the marine ecosystems. However, marine organisms are evolutionarily adapted for detecting the natural light of low intensity, regular cycles, and distinct spectra. For instance, the Calanus copepods, one of the most commonly found species of zooplankton, go through a pattern of a movement called “diel vertical migration.” During Arctic winter, they move to depths of 50 m guided by moonlight intensity.
Echinoderms synchronize, corals, and polychaete worms likewise broadcast their spawning events using annual and monthly variations in the lunar light. The authors found through in-water radiative transfer modeling that adult and larval stages of zooplankton, temperate marine organisms, and tropical corals are likely to respond to the artificial sky glow that is scattered in the atmosphere and then reflected to the ground. Waterside street lighting can go down the depths of 100m and artificial sky glow to depths of 70m.
The high sensitivity of marine animals to light
Davies and team highlighted that given the extent of ALAN across coastal areas and the high sensitivity of marine animals to light, a large part of seafloor habitat adjacent to urbanized coastlines is more likely to experience a level of light pollution that is already detectable to marine organisms. As a consequence, ALAN is impacting marine ecosystems.
The Light Emitting Diodes (LEDs) is one of the most energy-efficient and rapidly-developing lighting technologies today. This year, LED lights are expected to achieve a 61% penetrate rate in the global lighting market, according to BrandonGaille, and this will likely aggravate their impact in the marine ecosystems. The University of Plymouth researchers said that LEDs emit more short wavelength that can penetrate deeper into seawater at 30m depth. Many marine organisms are already sensitive to such a spectral signature.
Our World in Data, a scientific online publication that focuses on large global problems, also shares that having a light at night becomes more available to people nowadays as a country develops. Most countries around the world now have access to electricity. Those with the highest share of the population with access to electricity in 2016 data includes Australia (100%), Russia (100%), US (100%), Brazil (100%), Algeria (99.44%), and Peru (94.85%), among others.
Presently, about 40% of the world’s population also lives within 100 km of the coast. As economic activity and population density increases in the coastal zone, pressures on the coastal ecosystems also increase. World Ocean Review lists the following nations with the largest populations living in low-lying coastal areas: China (10% of the population), India (6%), Bangladesh (39%), Indonesia (20%), and Vietnam (53%). Meanwhile, the top nations classified by the proportion of the population in low-lying coastal areas are the Maldives, Bahamas, Bahrain, Suriname, and the Netherlands.
Lead author Davies, who is also a lecturer in marine conservation, told Science Daily that the areas exposed in their study are not trivial. Our results center on a busy marine area and show that the light from coastal urban centers is widespread across the seafloor, sub-surface, and sea surface of marine habitats. Yet, Plymouth is only one coastal city with 240,000 people. This is why the researches are calling for a more comprehensive review to better know the full impacts of coastal light pollution beyond Plymouth.
Plymouth Marine Laboratory’s Head of Science of Marine Biogeochemistry and Ocean Observations Dr. Tim Smyth also said that ALAN from coastal cities is likely to hurt the seafloor ecosystems that are providing us vital ecosystem services. He shared that during their fieldwork, they measured the win-water optics and above water light field. They also run an in-water light modeling simulations to map the light field across the whole network of Tamar Estuary. They also conducted a study in 2018 for over four nights when there was little or no green, blue, and red artificial light and moonlight.
Last year, a study from Binghamton University also found that light at night is also having a detrimental effect on amphibian populations.
Light pollution is the form of pollution that most people have forgotten to exist but it has become so widespread and universal. Its consequences are beyond just interfering with astronomical research and a waste of energy. It also disrupts our ecosystems. There are things we can do to help curb light pollution. The most obvious and the cheapest way would be to start turning things off when not in use. If you use outdoor lights, consider replacing them with low-glare and intelligently-designed fixtures. You may also choose to place motion sensors on important outdoor lamps.
Now, enjoy the blessings of a dark sky.