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.

High Latitude Epipelagic and Mesopelagic Scattering Layers—A Reference for Future Arctic Ecosystem Change

“…Most studies have focused on the more accessible fjord populations of fish and plankton, addressing Frontiers in Marine Science | www.frontiersin.orgspecific issues related to predator prey interactions and diel vertical migration (Falk-Petersen et al, 2004;Kaartvedt et al, 2008;Berge et al, 2009Berge et al, , 2014Dypvik et al, 2012). The current study is to our knowledge one of very few that incorporates biological and acoustic data from a larger part of the epipelagic and the mesopelagic zone (200-1,000 m depth), in the Northern North Atlantic on the boundary to the Arctic Ocean.…”

“…Berge et al (2009) showed that diel vertical migration during the Arctic winter is an important feature of the zooplankton community, especially for copepods in the epipelagial. Continued warming of the Arctic is likely to result in more complex ecotones across the Arctic marine system (Berge et al, 2014). Hatched region refers to area covered by transects t1-t9 of Melle et al (1993).…”

“…Baseline information regarding physical, chemical, and biological conditions is lacking for many parts of the Arctic (Wassmann and Reigstad, 2011; and crucial information on processes, species interactions, and behaviorial patterns recently uncovered (Berge et al, 2009(Berge et al, , 2014(Berge et al, , 2015Kraft et al, 2013;Last et al, 2016), suggests that current knowledge of the high Arctic marine ecosystem is incomplete. Thus, our understanding of the susceptibility of the Arctic ecosystem to a warmer ocean climate is limited and pathways along which changes will proceed are uncertain.…”

“…Thus, our understanding of the susceptibility of the Arctic ecosystem to a warmer ocean climate is limited and pathways along which changes will proceed are uncertain. Until recently it is the dynamics in the epipelagic zone, mostly focusing on fjord systems, that has been examined (Berge et al, 2009(Berge et al, , 2014(Berge et al, , 2015Kraft et al, 2013;Last et al, 2016). These investigations provide, however, little insight on the deeper living mesopelagic community and the coupling between the epipelagic and the mesopelagic communities (cf.…”

Toward quantifying the response of the oceans' biological pump to climate change

“…Studies such as Bopp et al (2013) have used global climate change biogeochemical models to capture the combined effects of climate-change mediated alteration of ocean circulation, properties such as temperature, pH and nutrient supply, and Net Primary Production (NPP) on the downward flux of POC. Other investigations, for example lab-and fieldbased experiments have targeted how aspects of climatechange (warming/ocean acidification, OA) will modify particular processes that influence the biological pump such as TEP (Transparent Exopolymer Particle) production (Taucher et al, 2015) or diurnal vertical migration (Berge et al, 2014). Pörtner et al (2014) in the Working Group 2 Fifth Assessment Report of the Intergovernmental Panel on Climate Change attempted to synthesize the findings of the growing number of studies into the sensitivity of the component parts of the biological pump to climate change.…”