Study highlights the European waters at greatest risk of harmful light pollution

Scientists have produced the first framework which can be used to assess whether a region is of Good Environmental Status in terms of light pollution.

The research set out to establish a means by which to assess whether a region is of Good Environmental Status (GES) when it comes to the risks posed to it by artificial light at night, otherwise known as ALAN. With no defined criteria of GES currently in existence for ALAN in European waters, the study team developed a new system which takes into account the light pollution being emitted by coastal towns and cities as well as the clarity of the sea water in particular locations and how easily light can penetrate through the water column. They then used existing data, including information previously published in a global atlas of nighttime light pollution, to highlight the European waters at greatest and least risk of harm.

It found that enclosed regions, bordered by land on several sides, tended to be where the risk of exposure to harmful light pollution was at its highest, with the Adriatic Sea, Baltic Sea and western Mediterranean Sea being the most impacted European waters. At the other end of the scale are more open areas of water such as Macaronesia (a region that includes the Canary Islands, Azores, Madeira and Cape Verde), the Barents Sea and the Iceland Sea. However, there were exceptions to those rules with the North Sea among those at higher risk due to the presence of oil and gas fields – and the infrastructure associated with that – adding significant levels of light pollution to what would otherwise be an open ocean setting.

Their research comes at a time when the European Union’s Marine Strategy Framework Directive (MSFD), introduced in 2008 to protect the marine ecosystem and biodiversity, is being reviewed. The authors hope their work, and the evidence it is based on, will ensure the impacts of ALAN are fully reflected in any future legislation.

Dr Thomas Davies, Associate Professor of Marine Conservation at the University of Plymouth, led the first ever study into the effects of light pollution on the marine environment in 2014 and is the new study’s lead author. He said: “Over many years, our research has repeatedly showed light pollution is significantly impacting many important coastal species. However, it is still not fully reflected in global policy, and while the MSFD was supposed to include measures linked to light pollution that has never fully materialised. The argument has always been that there isn’t the evidence to support any detailed legislation, meaning that light pollution remains – in policy terms at least – something of a hidden environmental threat. Our argument, based on this study and our other work since 2014, would be that is no longer the case and we believe we have clear evidence of risk and harm that urgently needs to be translated into meaningful action.”

Professor Tim Smyth, Director of Science at Plymouth Marine Laboratory, is the study’s senior author. He added: “Defining and quantifying Good Environmental Status requires more than measurement alone. It depends on combining global observations and mapping with expert scientific judgement on what a healthy ocean should look like. The 2021 Global Atlas of Artificial Light at Night Under the Sea, together with the extensive body of evidence generated over the past decade, has enabled us to assess this emerging pressure at a global scale. Alongside other stressors, such as underwater noise, it helps us build a more complete picture of cumulative human impacts on the ocean, providing the evidence base for effective action from global policy to local management.”

The study, published in the Ocean & Coastal Management journal, was written by scientists working as part of the AquaPLAN project, and also included authors from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), University of Pisa, Stazione Zoologica Anton Dohrn, and the Italian Institute for Environmental Protection and Research. Many of them are also part of the Global Ocean Artificial Light at Night Network (GOALANN), launched by Dr Davies and Professor Smyth at the United Nations Ocean Decade Conference in April 2024 and later endorsed by the UN as one of its Ocean Decade Actions.

Study co-author, Professor Elena Maggi, Professor in Ecology at the University of Pisa and AquaPLAN Project Coordinator, added: “We now have substantial evidence that artificial light at night can affect marine organisms and ecological processes. A key challenge is to translate that knowledge into approaches that allow us to identify where ecosystems are most at risk. This is one of the central aims of AquaPLAN: bringing together ecological knowledge and monitoring approaches to provide a stronger basis for assessing and mitigating the impacts of light pollution, and ultimately for finding more sustainable ways for human activities to coexist with coastal ecosystems This study represents an important step in that direction.”

Assessing the harmful effects of nighttime light pollution

The new framework developed through this study is informed by an existing approach developed for underwater noise, a form of marine pollution that is extensively covered in existing MSFD guidance. The research team developed separate risk scoring criteria for the water column and seabed, and used these to quantify the percentage of each regional sea which, based on satellite data and other assessments, was exposed to either nil, low, medium and high risk of harm. The authors say the methodology could also be applied globally and hope that by providing a scientifically grounded, operational and adaptable framework, they are demonstrating that effective management of marine light pollution can be achieved using existing knowledge and tools.

Addressing the growing threat of marine light pollution

Based on their work, there are a number of measures which the study’s authors say could be applied to reduce the impact of artificial lights on the marine environment. With many of the most impacted areas being tourist hotspots, they believe authorities in those regions could explore opportunities to make meaningful changes to their lighting infrastructure. This could include introducing shielding, dimming, or part-night lighting, as well as exploring ways to reduce light penetration into the sea through wavelength manipulation. They have also suggested designating dark spaces on and around islands, offering tourists an alternative experience to spending time overlooking seas bordered by artificial lighting.

Read the full study: Davies, T.W., Rendon Thompson, O.R., O’Driscoll, B., Seddon, R., Maggi, E., Rossi, F., Fabrizio Borsani, J. and Smyth, T. (2026). A proposed methodology for defining the criteria of ‘Good Environmental Status’ for artificial light at night in marine waters. Ocean & Coastal Management, 108383. DOI: https://doi.org/10.1016/j.ocecoaman.2026.108383.

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Image: The town of Primosten, a popular tourist destination on the Dalmatian coast of Adriatic sea in Croatia, at night. Credit Getty Images.