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Antarctic krill (Euphausia superba, hereafter krill) is a pelagic living crustacean and a key species in the Southern Ocean ecosystem. Krill builds up a huge biomass and its synchronized behavioral patterns, such as diel vertical migration (DVM), substantially impact ecosystem structure and carbon sequestration. However, the mechanistic basis of krill DVM is unknown and previous studies of krill behavior in the laboratory were challenged by complex behavior and large variability. Using a new experimental set-up, we recorded the swimming activity of individual wild-caught krill under light-dark cycles. Krill individuals exhibited differential phototactic responses to the light regime provided. However, using a new activity metric, we showed for the first time a consistent nocturnal increase in krill swimming activity in a controlled environment. Krill swimming activity in the new set-up was strongly synchronized with the light-dark cycle, similar to the diel vertical migration pattern of krill in the field when the krill were sampled for the experiment, demonstrated by hydroacoustic recordings. The new set-up presents a promising tool for investigating the mechanisms underlying krill behavioral patterns, which will increase our understanding of ecological interactions, the spatial distribution of populations, and their effects on biogeochemical cycles in the future., (© 2024. The Author(s).)

Imaging underwater can be particularly problematic and expensive given the harsh environmental conditions posed by salinity and for some deployments, pressure. To counter these difficulties, expensive waterproof pressure resistant housings are often used, commonly built from expensive materials such as titanium, if intended for long duration deployments. Further, environmental investigations often benefit from replicate data collection, which additionally increases study costs. In this paper we present a new camera system, developed with off the shelf and 3D printed cost effective components for use in shallow waters of <150 m depth. Integrating Raspberry Pi Zero W microcomputers with open source design files and software, it is hoped these camera systems will be of interest to the global marine and freshwater research communities., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2020 The Authors.)