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.
Highlights
Diel vertical migration (DVM) of zooplankton is a characteristic feature of the world’s oceans and lakes, and is suggested to be the largest synchronized movement of biomass on the planet (Hays, 2003)
We present the results from a study of DVM in the Arctic collected from four contrasting sites around the high Arctic archipelago of Svalbard (78– 808N) during the autumn equinox, combining netbased zooplankton collection with moored acoustic instruments at a time of strong diel change in illumination
We present evidence for the occurrence of distinctly different patterns of DVM between sites that are relatively close geographically with a zooplankton community comprising the same set of species (Fig. 6), but with contrasting hydrographic characteristics
Summary
Diel vertical migration (DVM) of zooplankton is a characteristic feature of the world’s oceans and lakes, and is suggested to be the largest synchronized movement of biomass on the planet (Hays, 2003). Our current state of knowledge does not yet permit any reliable identification of the species responsible for this behaviour, nor the mechanisms regulating the vertical positioning of the organisms. Both of these factors are critical for a holistic understanding of the patterns and processes governing Arctic marine systems, and are major obstacles for any predictive understanding of how ecosystem processes are likely be affected by the current warming of the Arctic Ocean and surrounding shelf seas
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