Klaipėda University, Klaipėda, Lithuania Trends in Ecology & Evolution Opinion A horizon scan for Arctic coastal biodiversity research: understanding changes requires international collaboration Jakob Thyrring 1, *, 1 Department of Ecoscience, Aarhus University, Aarhus, Denmark Philippe Archambault 2 , 2 Takuvik, ArcticNet, Québec Océan, Department of Biology, Université Laval, Québec, QC, Canada 3 Michael Burrows , 3 Scottish Association for Marine Science, Oban, Argyll, United Kingdom 4 Katrin Iken , 4 University of Alaska Fairbanks, Fairbanks, AK, USA 5 , Fernando P. Lima 5 CIBIO, InBIO LA, BIOPOLIS, Universidade do Porto, Porto, Portugal Joana Micael 6 , 6 Southwest Iceland Nature Research Centre, Suðurnesjabær, Iceland Markus Molis 7 , 7 UiT The Arctic University of Norway, Tromsø, Norway Catia Monteiro 5 , Sergej Olenin 8 , 8 Paul E. Renaud 9 , Ricardo A. Scrosati 10 , Rui Seabra 5 , Alexey A. Sukhotin 11 , Jan-Marcin Węsławski 12 , Nadescha Zwerschke 13 , and Mikael K. Sejr 1 Arctic coastal biodiversity faces increasing threats from anthropogenic activities and climate change. However, the effects on biodiversity are still poorly under- stood, hindering actions aimed at mitigating the impacts at a pan-Arctic scale. We present the results of a horizon scan that provides a road map to address knowledge gaps on the influence of anthropogenic activities, from increased shipping and harvesting to consequences of climate change including increas- ing temperatures, cryosphere loss, and freshwater runoff. Predictions on ecolog- ical change, species range expansions, and anthropogenic impacts on Arctic coasts are hampered by the lack of biodiversity data and scarcity of biological long-term monitoring programs. Filling these knowledge gaps will require coordi- nated international efforts and standardized experiments across the diverse eco- systems characterizing the Arctic. The Arctic coastline Based on the definition of the Arctic region given by the Conservation of Arctic Flora and Fauna group (Figure 1), one fifth of Earth’s coastlines are in the Arctic [1]. The Arctic coastal zone encompasses a wide variety of habitats, including rocky shores, sedimentary beaches, kelp beds, shallow lagoons, and river deltas (Figure 2). These Arctic coastal systems are influenced by a strong exchange of en- ergy and matter with terrestrial and open-ocean ecosystems and the cryosphere [2]. Healthy coastal ecosystems are of great importance to the millions of Arctic inhabitants [3] who depend on them for subsistence food sources and other ecosystem services underpinning their cultures and identities. Understanding threats to coastal biodiversity in a changing Arctic Arctic coastal ecosystems are experiencing pronounced environmental changes, with air temper- atures increasing three to seven times faster than the global average [4]. Biodiversity is consid- ered to facilitate many ecosystem services and resilience to change, and Arctic biodiversity faces a growing number of anthropogenic pressures, including fishing, mining, pollution, and the multifaceted impacts of climate change. Recent warming has increased melting of glaciers and sea ice, freshwater runoff, and permafrost thaw, which, together with increased storminess, has accelerated coastal erosion [5]. Rivers export large quantities of sediments, organic material, nutrients, and contaminants such as mercury to coastal habitats, and the magnitude and rates of physicochemical changes observed along Arctic coasts [6], which affect coastal species and their interactions at complex spatiotemporal scales, raise concerns about biodiversity responses and 460 Trends in Ecology & Evolution, May 2025, Vol. 40, No. 5 https://doi.org/10.1016/j.tree.2025.02.008 © 2025 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies. Highlights Current knowledge on coastal Arctic bio- diversity originates from a small number of study sites, but the Arctic includes more than a fifth of the world’s coastlines and its coastal biodiversity is increasingly experiencing pronounced effects of cli- mate change and other anthropogenic influences. The scarcity of baseline biodiversity data and a lack of large-scale comparative observations and experiments are limit- ing our capacity to detect commonalities in biodiversity responses to change at a pan-Arctic scale. A horizon scan identified threats to Arctic coastal biodiversity. Increased pan- Arctic coordination of long-term stan- dardized observations and field experi- ments is needed to understand the external impacts on ecological pro- cesses and to make predictions on coastal Arctic biodiversity on which ad- aptation and mitigation strategies can be based.