Unsynchronised and synchronised vertical migration of zooplankton in a high Arctic fjord

Abstract

We measured vertical migration of zooplankton in an arctic fjord at 79uN between June and September 2002 and transcending a period of continuous illumination to one of true day and night to investigate the changing influence of light cues on behavior. Observations made with a moored 300 kHz acoustic Doppler current profiler indicated that two modes of vertical migration occurred during the study period. During the weeks of continuous illumination, backscatter data indicated that there was no net vertical displacement of the population at any time during the 24-h period, but vertical velocity showed a continuous net downward movement in the surface layers and a net upward movement at depth. We interpreted this as unsynchronized vertical migrations by individuals with upward trajectories that slowed closer to the surface and downward trajectories that were most rapid in their initial phases. Synchronized migrations, seen as an upward and downward movement of scattering layers at dusk and dawn respectively, began once true nighttime resumed toward autumn. It is likely that the relative rate of change in light was used as the proximal cue for synchronized migrations. Concurrent net samples identified Calanus finmarchicus and C. glacialis as the most likely contributors to the unsynchronized migration patterns. The high backscatter of the synchronized scattering layers suggests that they included additional taxa such as the euphausiid Thysanoessa spp., the pteropod Limacina helicina, or the hyperiid amphipod Themisto spp.

Acoustic insights into the zooplankton dynamics of the eastern Weddell Sea

“…al., 2001;BlachowiakSamolyk et. al., 2006;Cottier et al, 2006;Falk-Petersen et al, 2008;Berge et al, 2009;Benoit et al, 2010;Rabindranath et al, 2010).…”

“…Although zooplankton populations do not migrate vertically in a synchronised manner during midnight sun conditions, Cottier et al (2006) and Wallace et al (2010) found evidence that individuals within those populations performed forays in and out of the surface layers throughout the 24-h cycle. While their backscatter data indicated that there was no net vertical displacement of the population at any time during the 24-h period, the vertical velocity showed a continuous net downward movement in the surface layers and a net upward movement at depth, which represents the so-called unsynchronised DVM.…”

Towards a correct description of zooplankton feeding in models: Taking into account food-mediated unsynchronized vertical migration

“…Thus the observed non-existence of local functional response is presumably a consequence of complex foraging behaviour of zooplankton at intermediate time and space scales and not a result of noise. Note that this phenomenon is rather different from the dailybased vertical migration pattern since it implies an exchange of organisms between different layers in a unsynchronized way without a pronounced alteration of the vertical profile of zooplankton (Leising et al, 2005;Cottier et al, 2006).…”

“…Feeding of zooplankton in the ocean (or deep lakes) implies existence of complex foraging cycles characterized by permanent exchange of grazers between surface and deep layers (Pearre, 1979;Leising et al, 2005, Cottier et al, 2006. In this paper, we provide an example of such unsynchronized vertical migration for herbivorous copepods based on our field data.…”

“…They move to those depths either to digest the food that they have grazed or to escape from predators or due to some other reasons (Dagg and Wyman, 1983;Cottier et al, 2006). Thus the observed non-existence of local functional response is presumably a consequence of complex foraging behaviour of zooplankton at intermediate time and space scales and not a result of noise.…”