Jellyfish locomotion and orientation have been studied in the past both in the laboratory, testing mostly small jellyfish, and in the field, where it was impossible to control the seawater currents. Utilizing an outdoor water flume, we tested the locomotion of jellyfish when swimming against and with currents of up to 4.5 cm s−1. We used adult jellyfish from two of the most abundant species in the eastern Mediterranean, Rhopilema nomadica and Rhizostoma pulmo, and measured their pulsation frequency and swimming speed relative to the water. While pulsation frequency was not affected by the water velocity, jellyfish swam faster against the current than with it. This finding suggests that jellyfish possess a sensory ability, whose mechanism is currently unknown, enabling them to gauge the flow and react to it, possibly in order to reduce the risk of stranding.
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We would like to thank Elad Lando, Vera Brekhman, Gadi Piriatinskiy, Gur Mizrahi, Dor Edelist, and Sara Orca who helped in the setup of the jellyfish flume and in the experiments, Gennadi Zaslavski for his assistance in video data acquisition, Ido Dekel for his help in digitization, Corrine Jacobs and Karin Olsson for their insights and comments during the preparation of this manuscript, and the many students from the Leon H.Charney School of Marine Sciences, University of Haifa, who helped to collect the jellyfish. We thank the Israel Oceanographic and Limnological Research (IOLR) for sharing with us their seawater flow systems and flumes and for their technical support. This research was supported by the Israel Electric Corporation.
© 2019, The Author(s).
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