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First assessment of night-light risk in European seas ranks enclosed waters highest
Plymouth scientists rank the Adriatic, Baltic and western Mediterranean as the European seas most at risk from artificial light at night. Their method is the first attempt at a status test for night light, which the EU's 2008 marine directive lacks as it comes up for review.
The Scientist · Science desk
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What happened
- The method scores each sea on light emitted by coastal towns and cities, on water clarity, and on how easily light penetrates the water column.
- The lowest-risk waters were open ones: Macaronesia, which includes the Canary Islands and the Azores, along with the Barents Sea and the Iceland Sea.
- Waters around the UK, the Greater North Sea and the Celtic Seas, came out largely at medium to low risk.
- The study appeared in Ocean & Coastal Management, written by AquaPLAN project scientists with Cefas, the University of Pisa, Genoa Marine Centre and Italy's environmental protection institute.
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Why it matters
- decision EU officials reviewing the marine directive now have a worked method in hand, so the evidence gap Davies says has blocked light rules is harder to cite.
- constraint Any standard built on this method inherits a threshold set partly by expert judgment, so regulators would have to defend in public where good status begins.
- exposure If a light standard follows this method, North Sea oil and gas operators fall within it, because their platforms raise the score of an otherwise open-ocean setting.
- exposure Coastal states on the Adriatic, Baltic and western Mediterranean would carry the largest share of any lighting cuts under a standard drawn this way.
Those inputs describe exposure. The score says where light from shore is most likely to get into the water column and reach the life in it [c1, c3]. The case that the light does damage rests on a decade of separate studies. Thomas Davies, associate professor of marine conservation at the University of Plymouth, is the lead author [17]. According to phys.org, he led the first study of light pollution's effects on the marine environment in 2014 [17]. He said, "Over many years, our research has repeatedly shown light pollution is significantly impacting many important coastal species." [1]
The enclosed-sea pattern is what those inputs would predict. The study found that seas bordered by land on several sides tended to score highest [9]. A basin with lit coastline on several sides takes in light from all of them, and open water at the far end of the scale has fewer shores close by [c3, c6]. The phys.org account does not report the underlying scores, the resolution of the map, or where the line between good and poor status was drawn.
That line had to be set from scratch, because no defined criteria for good environmental status exist for night light in European waters [6]. The senior author says it is partly a judgment call. Tim Smyth, director of science at Plymouth Marine Laboratory [18], said, "Defining and quantifying good environmental status requires more than measurement alone. It depends on combining global observations and mapping with expert scientific judgment on what a healthy ocean should look like." [15] The observations include data from the 2021 Global Atlas of Artificial Light at Night Under the Sea [c4, c14]. Smyth said the atlas, together with a decade of evidence, made a global-scale assessment possible [16].
The score also picks up offshore lighting [c4, c8]. In the North Sea, oil and gas fields and the infrastructure around them added significant light to what would otherwise be an open-ocean setting, according to the study [12].
The policy target is the EU's Marine Strategy Framework Directive (MSFD), which the authors hope will reflect the effects of night light when its review is done [13]. Davies said that "while the MSFD was supposed to include measures linked to light pollution, that has never fully materialized." [2] He named the objection that has held things up: "The argument has always been that there isn't the evidence to support any detailed legislation" [4]. On the strength of this study and the team's work since 2014, he said, "we believe we have clear evidence of risk and harm that urgently needs to be translated into meaningful action." [3]
In my view the method is a sound basis for a regulatory test, provided the status threshold is published and argued in the open. Smyth's own description puts expert judgment inside it [15]. Many of the authors also belong to the Global Ocean Artificial Light at Night Network, which Davies and Smyth launched at the UN Ocean Decade Conference in April 2024 and which the UN later endorsed as an Ocean Decade Action [19].
What to watch
- Whether the EU's review of the Marine Strategy Framework Directive adds a criterion for artificial light at night, and on what threshold.
- Species surveys in the Adriatic, Baltic or western Mediterranean that test whether high-risk scores match measured effects on coastal life.
- Publication of the scores and status thresholds behind the ranking, so other groups can rerun it with their own water-clarity data.