| Summary: | The Arctic is defined by a seasonal light regime extending between 24-hour light (Midnight Sun) and 24-hour dark (Polar Night). Light itself acts as an important cue for marine zooplankton, dictating their orientation/navigation and vertical migration, prey detection and predator avoidance, and population dynamics/reproductive strategies. Changes in the spectral, intensity, and duration components of downwelling irradiance during Midnight Sun and Polar Night contribute to the annual Arctic light climate, and to what characteristics of light are used for zooplankton visual processes. Additionally, as the Arctic region is warming at an alarming rate, the loss of annual sea ice and snow coverage is projected to increase incoming illumination into the water column, impacting zooplankton visual systems, trophic dynamics, and predator-prey interactions. ☐ Given the marked differences in annual light climate at high latitudes, the objective of this study was to determine the behavioral responses of zooplankton species to spectral and irradiance light stimuli during Midnight Sun and Polar Night. The copepod species Metridia longa copepods were selected as the target species for this research due to their biomass in Atlantic-Arctic waters, vertical migration behaviors, and bioluminescent capabilities. While Polar Night twilight peak emissions are blue dominant (λmax = 455 nm) there is a shift towards green light (λmax = 550 nm) availability during Midnight Sun due to spring phytoplankton blooms and suspended particulate matter in the water column. Therefore, it was hypothesized that copepods will exhibit a broad spectral response sensitivity in the blue-green wavelengths in order to compensate for the annual shifts in available spectra. Additionally, it is expected that M. longa copepods will have a heightened irradiance response during Polar Night compared to Midnight Sun. Zooplankton visual systems are often more sensitive in low light conditions, thus it is hypothesized that irradiance responses will be increased ...
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