Abstract
Abstract. Hudson Bay is a large seasonally ice-covered Canadian inland sea connected to the Arctic Ocean and North Atlantic through Foxe Basin and Hudson Strait. This study investigates zooplankton distribution, dynamics, and factors controlling them during open-water and ice cover periods (from September 2016 to October 2017) in Hudson Bay. A mooring equipped with two acoustic Doppler current profilers (ADCPs) and a sediment trap was deployed in September 2016 in Hudson Bay ∼190 km northeast from the port of Churchill. The backscatter intensity and vertical velocity time series showed a pattern typical for zooplankton diel vertical migration (DVM). The sediment trap collected five zooplankton taxa including two calanoid copepods (Calanus glacialis and Pseudocalanus spp.), a pelagic sea snail (Limacina helicina), a gelatinous arrow worm (Parasagitta elegans), and an amphipod (Themisto libellula). From the acquired acoustic data we observed the interaction of DVM with multiple factors including lunar light, tides, and water and sea ice dynamics. Solar illuminance was the major factor determining migration pattern, but unlike at some other polar and subpolar regions, moonlight had little effect on DVM, while tidal dynamics are important. The presented data constitute the first-ever observed DVM in Hudson Bay during winter and its interaction with the tidal dynamics.
Highlights
The diel vertical migration (DVM) of zooplankton is a synchronized movement of individuals through the water column and is considered to be the largest daily synchronized migration of biomass in the ocean (Brierley, 2014)
Even though acoustic backscatter from the single-frequency acoustic Doppler current profilers (ADCPs) does not provide any information on the identity of zooplankton species involved in DVM, signal strength can provide an indication of zooplankton presence provided there is information on the zooplankton species
A 1-year-long acoustic backscatter and vertical velocity time series, obtained using a 300 kHz ADCP on a mooring deployed from September 2016 to October 2017 in southeast Hudson Bay (∼ 190 km northeast from the port of Churchill), revealed a distinct diurnal pattern consistent with zooplankton diel vertical migration (DVM)
Summary
The diel vertical migration (DVM) of zooplankton is a synchronized movement of individuals through the water column and is considered to be the largest daily synchronized migration of biomass in the ocean (Brierley, 2014). (3) there is a twilight DVM pattern when zooplankton ascend at sunset, descend around midnight, ascend again, and descend at sunset (Cohen and Forward, 2005; Valle-Levinson et al, 2014). The following research question needs to be addressed: what sets
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