Abstract
The herbivorous Antarctic copepod Calanoides acutus overwinters inactively in a resting stage (diapause) at depths below 500 m. It is assumed that during diapause C. acutus is neutrally buoyant in order to retain energy reserves otherwise depleted by swimming activities. However, so far, no experimental observations on its buoyancy have been reported and our knowledge of buoyancy regulation mechanisms is incomplete. In the present study, species-specific differences in buoyancy were assessed visually. Observations were made of specimens from the diapausing cohort of C. acutus and compared to another herbivorous copepod Calanus propinquus, which overwinters actively feeding in the upper water layers. Freshly caught copepods were anaesthetized in a 3-amino-benzoic acid ethyl ester (MS222) in seawater solution in order to exclude the influence of swimming movements on buoyancy control. It was shown that C. propinquus was negatively buoyant, whereas diapausing C. acutus remained neutrally buoyant. This is the first record that neutral buoyancy in diapausing copepods is maintained by the biochemical body composition without the additional need of swimming movements.
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Acknowledgments
We would like to thank the captain and crew of R/V Polarstern for their competent support during the cruise. Special thanks to Carolin Hauer for her skilful help during zooplankton sampling on board. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme “Antarctic Research with comparative investigations in Arctic ice areas” (Grant numbers AU 175/6 and SA 1713/3). http://www.spp-antarktisforschung.de/de.
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Schründer, S., Schnack-Schiel, S.B., Auel, H. et al. Observations of neutral buoyancy in diapausing copepods Calanoides acutus during Antarctic winter. Polar Biol 37, 1369–1371 (2014). https://doi.org/10.1007/s00300-014-1525-7
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DOI: https://doi.org/10.1007/s00300-014-1525-7