Light exerts a twofold fundamental impact on life in the ocean. It not only drives photosynthesis, forming the energetic foundation for all higher trophic levels from the bottom up, but also shapes top-down ecological dynamics through vision. Many higher-level predators, including birds, fish, seals, and whales, rely on vision—and thus light—to successfully locate their prey. Light is arguably also the most variable environmental factor, yet it is often overlooked in ecological studies. Light intensity varies over time and space, with diurnal cycles of incoming sunlight, moonlight, and starlight. These variations are further modulated by changes in cloudiness, water clarity, sea ice, and differences in day length across latitudes. Surface light intensities can vary by more than 10 orders of magnitude over a day. This range is comparable to the attenuation of light observed between depths of 200 and 1000 meters in the mesopelagic zone during daytime in clear waters.
This keynote explores the ecological significance of light for life in the open ocean and unites insights from the depths of the mesopelagic zone to the shallow banks of shelf-sea ecosystems. From the Mediterranean to the ice-covered Arctic Ocean, Tom connects mechanisms and emergent ecology, scaling from individual behaviours and species interactions to macroecological patterns. Key questions include: Can light act as a barrier to species distribution? How might an ice-free Arctic Ocean in the future impact fish migration and distribution? What role does the full moon play in the spawning behaviour of Atlantic bluefin tuna? How does the seafloor make zooplankton and micronekton vulnerable to predation? And, does the artificial light from research vessels at night skew our observations and understanding of marine ecosystems?
Bio
Tom Langbehn is a marine ecologist and an “ocean-going modeller” with a keen interest in global change ecology, evolution, and sustainable fisheries. He has a special fascination with polar ecosystems, particularly their extreme seasonality, and how life operates in the vast expanse and perpetual twilight of the mesopelagic zone. In his work, Tom combines theory and modelling with observations and field experiments. This approach helps him explore the mechanics of life in the ocean, including what creates, drives, and maintains diversity in traits, functions, species, and strategies across various dimensions such as latitude, season, and depth. Specifically, his research focuses on pelagic ecology, examining how the environment, predators, and prey collectively influence the abundance, distribution, and behaviour of zooplankton and fish. Tom holds a PhD from the University of Bergen, where he currently works as a researcher in the Theoretical Ecology Group within the Department of Biological Sciences.
