| Summary: | In the featureless pelagic environment, the submarine light field plays an important role in structuring population dynamics by influencing a variety of biological processes and trophic interactions. For many marine organisms, bioluminescence is the main visual stimulus as downwelling atmospheric light attenuates with depth. However, the distribution of bioluminescent plankton is variable with depth, and bioluminescent species differ in the intensity of their emissions, causing the bioluminescent light field to be dependent on the composition and distribution of the bioluminescent community. Mechanically-stimulated bioluminescence, or bioluminescence potential, interacts with background ambient light to influence light-mediated behaviors, such as visual search for predators or prey, thus having a potentially large influence on ecosystem dynamics and function through trophic interactions. Nevertheless, bioluminescent community dynamics and the role of bioluminescence in larger ecosystem function remain to be characterized for many systems. In order to understand the ecological role of bioluminescence in dim environments this study investigated winter bioluminescent communities in Kongsfjord, Svalbard, a high Arctic fjord (78°N, 55°E), during January 2014. Kongsfjord during this time of the year experiences low atmospheric irradiance for an extended period, due to the sun being below the horizon for the duration of the polar night. Therefore, the amount of light available for visually-mediated behaviors and trophic interactions in the pelagic zone is also dim. However, bioluminescence occurs throughout the water column, and some overwintering visual predators in Kongsfjord have been shown to feed on bioluminescent taxa. Therefore, Kongsfjord represents a unique environment for investigating shallow water bioluminescent communities and the trophic role of bioluminescence within these communities. With this study, I report the depth distribution and taxonomic composition of bioluminescent plankton as determined by a ...
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