Harmful light pollution reaches up to 75% of the seafloor surrounding coastal cities

A ground-breaking new study has revealed for the first time the extent to which light pollution from coastal cities reaches nearby seafloor environments. It revealed that up to 75% of the 3D space surrounding the habitats can be exposed to light pollution, which can have highly damaging effects.

artificial skyglow
Light pollution from coastal cities like Plymouth (UK) have been shown to reach over 75% of surrounding seafloor habitats

Around 3/4 of world’s megacities are now located in coastal regions, with the populations of those regions set to double by 2060. All these people living on the border between land and sea is bound to have a number of negative impacts on the natural environments surrounding them, such as increased emissions of greenhouse gases and toxic chemicals, destruction of crucial habitats, displacement or extinctions of endemic species and pollution of waste materials. However one of the most underestimated impacts major coastal cities can have is actually artificial light pollution at night, especially in the surrounding marine environment. Now a new study, by researchers based in Plymouth (UK), has revealed for the first time the extent of this unseen danger and highlighted the potential impacts that can follow it.

Studying ‘skyglow’

It was New York City which was first and most famously coined ‘the city that never sleeps’, but in reality most major cities today remain as active at night as they do in the day. The result being that the night sky surrounding them are constantly illuminated in the artificial glow of streetlights and skyscrapers. This is known by scientists as skyglow and whilst it is obvious to those looking up at the night sky, the effects it can have are mostly unseen. It has long been suspected that this unnatural phenomenon can create widespread light pollution in the marine environment, with researchers already showing that many marine species will be negatively impacted if the problem was severe enough. However the extent of the problem has never been studied due to the technical difficulties posed by measuring light pollution underwater at night.

plymouth at night
Another example of the artificial skyglow in the night sky surrounding Plymouth Sound

That is until a new study, by a team of ground-breaking researchers based in Plymouth, recently managed to assess the extent of the issue for the first time. Using advanced study techniques the team, made up of scientists from Plymouth University, Bangor University, University of Strathclyde and Plymouth Marine Laboratory, focused on the Plymouth Sound and Tamar Estuary which together form a busy waterway and are home to the largest naval port in Western Europe. Over four nights in 2018, when there was little or no moonlight, they shone artificial light mimicking the city’s skyglow at the surface and, using a combination of mapping and radiative transfer modelling tools, were able to measure exposure at the surface, beneath the surface, and at the seafloor. They recently published their results in a new paper in Scientific Reports of the journal Nature.

A pervasive problem

Their results highlighted that between 70-76% of the 3D space surrounding seafloor habitats was exposed to light pollution caused by their artificial skyglow. This alarming statistic strongly suggests that this issue is likely to be prevalent in the surrounding marine environments of almost all major coastal cities. The team also found that the main reason that the exposure is so high is due to the switch to LED lights in most modern cities. They found that the blue and green wavelengths in these types of lights are well suited to penetrating the surface and water column of the ocean. Overall their findings suggest that artificial skyglow is a much more widespread cause of light pollution in the marine environment than previously estimated.

LED lights
A switch to LED lights in most streetlights and buildings is in part responsible for how much light reaches the seafloor

Impacts on wildlife

Given what we now know about the extent of artificial light pollution surrounding coastal cities it raises many questions about what issues it may cause for marine life. Previous research from Plymouth University this year has also shown how light pollution can disrupt navigation and associated behaviours for those species that rely on moonlight for navigation, such as sand hoppers. Many other species such as clownfish also heavily rely on lunar cycles for reproduction which can also be effected. There are many other potential issues such as animals losing their natural camouflage at night or getting increasingly stressed, and if too many species are effected then it could even lead to ecosystem-wide effects. However because the problem of light pollution has largely been ignored until now the research into its exact effects on individual species is just not there yet.

underwater moonlight
One of the main problem with light pollution at night is that creatures can confuse it for moonlight which they can use as a cue for many vital behaviours

Looking forward

It is because of the uncertainty surrounding the impacts of artificial light pollution on marine species that the authors of the new study end their paper by stating that ‘a comprehensive understanding of the impacts are urgently needed’. In a recent press release lead author Dr Thomas Davies explained that the problem “is widespread across the sea surface, sub surface and seafloor of adjacent marine habitats” and that “unless we take action now it is clear that light pollution on the seafloor is likely to be globally widespread, increasing in intensity and extent, and putting marine habitats at risk”. Thankfully the findings he and his team uncovered during their study have revealed to the entire scientific community that artificial skyglow and light pollution has the potential to be a dangerous issue. Hopefully this will be enough for it to be taken seriously and for more much-needed research to be undertaken.

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