UNIVERSITY OF BERGEN

Department of
Biological Sciences

Researcher, PhD
Tom J. Langbehn

Light and Vision as Key Drivers in Marine Ecology

I am a marine ecologist, ocean-going modeler, and scientific illustrator. My interests span evolution, global change ecology, biological oceanography, and sustainable fisheries. I specialize in pelagic ecology, with a focus on understanding the mechanisms underlying interactions between indidivuals or species and between organisms and their environment. My aspiration is to contribute to the fundamental understanding of marine ecosystems and increase our ability to predict their responses and dynamics to ultimately inform their sustainable management.

My work integrates theory and modeling with observations and field experiments. Over the past decade, light and vision as key drivers in marine ecology have been cross-cutting themes in my research. I am particularly fascinated by high-latitude polar ecosystems, drawn to their extreme seasonality, and life inhabiting the perpetual twilight of the mesopelagic zone.

 

I am currently leading the following project

Trond Mohn Project: Advection and trophic subsidies
The world’s open ocean may appear barren, but is it its low productivity, transported by currents, that fuels the rich ecosystems along shelves and coasts? This TMF Starting Grant Project (2025-2028) will investigate where and when prey from the open ocean becomes accessible to predators, and how advected biomass influences production, life-history strategies, and species distributions in the receiving ecosystems.

I am currently a collaborator on the following project

Project: How can fisheries contribute more to a sustainable future?
The ocean harbours half the global primary production but produces only 2% of human food and 6% of dietary protein. This project takes a step back, and together with key stakeholders considers fisheries as a food system and reimagines their role when the SGDs, the Paris Agreement, and the Convention on Biological Diversity are allowed to define the objective as maximizing food production while minimizing footprint.

Research highlights

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Light limits distributions at high latitudes

State-of-the-art correlative species distribution models predict the poleward expansion of boreal species into high-latitude environments based on environmental conditions but often overlook the light environment. In contrast, our mechanistic models, which account for temperature-dependent bioenergetics and light-driven encounters, reveal that seasonal light environments act as a barrier, preventing key species groups from colonizing high-latitude oceans despite climate change.

Ljungström G, Langbehn T, Jørgensen C. 2024.
Bergmann patterns in planktivorous fishes: A light-size or a zooplankton community-size rule is just as valid explanation as the temperature-size rule
Global Ecology and Biogeography. 33: 17-33. [ doi:10.1111/geb.13782 ] [ open access ] [ pdf ]
Langbehn T, Aksnes DL, Kaartvedt S, Fiksen Ø, Ljungström G, Jørgensen C. 2022.
Poleward distribution of mesopelagic fishes is constrained by seasonality in light
Global Ecology and Biogeography. 31: 546-561. [ doi:10.1111/geb.13446 ] [ open access ] [ pdf ]
Ljungström G, Langbehn TJ, Jørgensen C. 2021.
Light and energetics at seasonal extremes limit poleward range shifts
Nature Climate Change. 11: 530-536. [ doi:10.1038/s41558-021-01045-2 ] [ Video abstract ] [ Read for free on Nature website ]

 

Light as a Top-Down Driver

Most studies focus on light as a bottom-up driver of primary production; my work emphasizes its top-down control. Many predators, including birds, fish, squid, seals, whales, and some invertebrates, rely on vision to locate their prey. These visual predator-prey dynamics critically shape the vertical distribution, migration behaviors, and life-history strategies of marine life. When this perspective is considered, it often prompts a new and deeper understanding of marine ecological processes.

Ottmann D, Langbehn TJ, Reglero P, Alvarez-Berastegui D, Fiksen Ø. 2023.
Model of mesopelagic fish predation on eggs and larvae shows benefits of tuna spawning under full moon
Limnology and Oceanography. 68: 2632-2641. [ doi:10.1002/lno.12465 ] [ open access ] [ pdf ]
Langbehn TJ, Aksnes DL, Kaartvedt S, Fiksen Ø, Jørgensen C. 2019.
Light comfort zone in a mesopelagic fish emerges from adaptive behaviour along a latitudinal gradient
Marine Ecology Progress Series. 623: 161-174. [ doi:10.3354/meps13024 ] [ open access ] [ pdf ] [ Online supplement ]
Kaartvedt S, Aksnes DL, Langbehn TJ. 2019.
Enlightening the ocean’s twilight zone
ICES Journal of Marine Science. 76: 803-812. [ doi:10.1093/icesjms/fsz010 ] [ open access ] [ pdf ]

 

Light and a Changing Riskscape in the Future Arctic Ocean

Arctic sea-ice loss is rapidly transforming the entire ecosystem. Less ice means reduced shading and increased light, boosting the foraging efficiency of planktivorous fish. Arctic copepods, being particularly large, are at greater risk due to their visibility to predators, which could lead to a community-wide shift toward smaller, less fat individuals or species, potentially causing ripple effects throughout the Arctic food web.

Langbehn TJ, Aarflot JM, Freer JJ, Varpe Ø. 2023.
Visual predation risk and spatial distributions of large Arctic copepods along gradients of sea ice and bottom depth
Limnology and Oceanography. 68: 1388-1405. [ doi:10.1002/lno.12354 ] [ open access ] [ pdf ]
Langbehn TJ, Varpe Ø. 2017.
Sea-ice loss boosts visual search: fish foraging and changing pelagic interactions in polar oceans
Global Change Biology. 23: 5318-5330. [ doi:10.1111/gcb.13797 ] [ open access ] [ pdf ]

 

Artificial Light At Night

Almost all biological observations made at sea during the night occur within an artificial light beam. Our work, including a manuscript in progress, shows that normal ship lights can cause both attraction and avoidance behaviors, significantly impacting the community composition, behaviors, and vertical distribution of pelagic organisms. This highlights the challenge of obtaining unbiased data from hull-mounted acoustics, vertical net hauls, or in-situ observations using optical instruments that depend on external light sources.

Geoffroy M, Langbehn T, Priou P, Varpe Ø, Johnsen G, Le Bris A, Fisher JAD, Daase M, McKee D, Cohen J, Berge J. 2021.
Pelagic organisms avoid white, blue, and red artificial light from scientific instruments
Scientific Reports. 11: 14941. [ doi:10.1038/s41598-021-94355-6 ] [ open access ] [ pdf ]

 

Insights outside

My work encompasses both numerical modelling as well as observational and experimental field studies. Most recently, we uncovered that the rapid decline of blue mussels along the Norwegian coast cannot be attributed to climate change but is more likely a conservation success. This is due to populations of predatory drilling snails recovering from pollution-induced sterility, which has now been washed out of the system.

Meister N, Langbehn TJ, Varpe Ø, Jørgensen C. 2023.
Blue mussels in western Norway have vanished where in reach of crawling predators
Marine Ecology Progress Series. 721: 85-101. [ doi:10.3354/meps14416 ] [ open access ] [ pdf ]

 

Visual storytelling - Our World in Figures

The three things I like to nerd out about most are biology, coding, and data visualization. I am happiest when they all come together. I've always been a visual learner; to fully grasp a concept, I need to see it or, even better, sketch it out. For me, working visually is not just a tool for communicating science—it iss also a way to think, analyze, and understand.

I create visualizations for my own publications, talks, and posters, and I have become the go-to person for colleagues seeking help to visualize their science. I have also designed logos for projects and research groups, including our own, and created short videos for key publications. I regularly share my passion for visual storytelling, along with tips and tools, in science communication classes for diverse audiences.

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