Bioluminescence in the arctic polar night
Date
2015
Authors
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Publisher
University of Delaware
Abstract
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 profiled bathyphotometer in Kongsfjord, and create a pelagic photon budget for atmosphere-derived scalar irradiance and bioluminescence potential. To explore the potential for bioluminescence to affect food-web dynamics in Kongsfjord, I also model the influence of bioluminescent light fields from measured communities on a relevant visual trophic interaction. The 20m to 40m depth range in Kongfjord represented a transition zone in which taxonomic abundance, diversity indices, and bioluminescence potential indicated shallow and deep bioluminescent communities. Bioluminescence potential in the water column peaked at 80m, and dinoflagellates were the most abundant taxonomic group at or above 20m, while the copepod Metridia longa was the most abundant taxon below 20m. By quantifying the visual sensitivities of a key micronekton, the euphausiid Thysanoessa inermis, community-generated bioluminescent light fields measured in Kongsfjord were applied to a visual model for krill viewing one of its winter predators, the little auk (Alle alle ). Depending on the depth of T. inermis, and therefore the intensity of background space-light, emissions from bioluminescent communities in Kongsfjord either illuminated or camouflaged the diving little auk. This study also determined that the number of photons contributed to the pelagic photon budget by bioluminescence in Kongsfjord surpassed atmosphere-derived scalar irradiance between 20 and 40m. At depths as shallow as 60m, bioluminescence contributes 98% or more of pelagic photons, indicating that during winter in Kongsfjord, bioluminescence plays a disproportionate role in predator-prey dynamics during the day than in other shallow daytime ecosystems.