title: Arctic complexity: a case study on diel vertical migration of zooplankton.
abstract: Diel vertical migration (DVM) of zooplankton is a global phenomenon, characteristic of both marine and limnic environments. At high latitudes, patterns of DVM have been documented, but rather little knowledge exists regarding which species perform this ecologically important behaviour. Also, in the Arctic, the vertically migrating components of the zooplankton community are usually regarded as a single sound scattering layer (SSL) performing synchronized patterns of migration directly controlled by ambient light. Here, we present evidence for hitherto unknown complexity of Arctic marine systems, where zooplankton form multiple aggregations through the water column seen via acoustics as distinct SSLs. We show that while the initiation of DVM during the autumnal equinox is light mediated, the vertical positioning of the migrants during day is linked more to the thermal characteristics of water masses than to irradiance. During night, phytoplankton biomass is shown to be the most important factor determining the vertical positioning of all migrating taxa. Further, we develop a novel way of representing acoustic data in the form of a Sound Image (SI) that enables a direct comparison of the relative importance of each potential scatterer based upon the theoretical contribution of their backscatter. Based on our comparison of locations with contrasting hydrography, we conclude that a continued warming of the Arctic is likely to result in more complex ecotones across the Arctic marine system.
authors.affiliation: Faculty of Biosciences, Fisheries and Economics , University of Tromsø , 9037 Tromsø , Norway ; The University Centre in Svalbard , N-9171 Longyearbyen , Norway.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Berge
authors.affiliation: Scottish Association for Marine Science , Scottish Marine Institute , Oban, Argyll PA37 1QA , UK.
authors.forename: Finlo
authors.initials: F
authors.lastname: Cottier
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway ; Akvaplan-Niva , Fram Centre for Climate and the Environment , N-9296 Tromsø , Norway.
authors.forename: Oystein
authors.initials: O
authors.lastname: Varpe
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway ; Akvaplan-Niva , Fram Centre for Climate and the Environment , N-9296 Tromsø , Norway.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Renaud
authors.affiliation: Faculty of Biosciences, Fisheries and Economics , University of Tromsø , 9037 Tromsø , Norway ; Akvaplan-Niva , Fram Centre for Climate and the Environment , N-9296 Tromsø , Norway.
authors.forename: Stig
authors.initials: S
authors.lastname: Falk-Petersen
authors.affiliation: Institute of Oceanology Polish Academy of Sciences , Powstancow Warszawy 55, 81-712 Sopot , Poland.
authors.forename: Sawomir
authors.initials: S
authors.lastname: Kwasniewski
authors.affiliation: Scottish Association for Marine Science , Scottish Marine Institute , Oban, Argyll PA37 1QA , UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Griffiths
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway.
authors.forename: Janne E
authors.initials: JE
authors.lastname: Søreide
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway ; Department of Biology, Trondhjem Biological Station, Applied Underwater Robotics Laboratory , Norwegian University of Science & Technology (NTNU) , N-7491 Trondheim , Norway.
authors.forename: Geir
authors.initials: G
authors.lastname: Johnsen
authors.affiliation: Faculty of Biosciences, Fisheries and Economics , University of Tromsø , 9037 Tromsø , Norway ; The University Centre in Svalbard , N-9171 Longyearbyen , Norway.
authors.forename: Anais
authors.initials: A
authors.lastname: Aubert
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway.
authors.forename: Oda
authors.initials: O
authors.lastname: Bjærke
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway ; Norwegian Polar Institute, Fram Centre for Climate and the Environment , N-9296 Tromsø , Norway.
authors.forename: Johanna
authors.initials: J
authors.lastname: Hovinen
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway.
authors.forename: Signe
authors.initials: S
authors.lastname: Jung-Madsen
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway.
authors.forename: Martha
authors.initials: M
authors.lastname: Tveit
authors.affiliation: The University Centre in Svalbard , N-9171 Longyearbyen , Norway ; Faculty of Biological and Environmental Sciences , University of Helsinki , FI-00014 Helsinki , Finland.
authors.forename: Sanna
authors.initials: S
authors.lastname: Majaneva
keywords: ADCP; Arctic; acoustics; complexity; diel vertical migration; light regime; physical forcing; predator–prey interactions; water masses; zooplankton