Abstract
A multi-scale approach was used to evaluate which spatial gradient of environmental variability is the most important in structuring zooplankton diversity in the West Spitsbergen Current (WSC). The WSC is the main conveyor of warm and biologically rich Atlantic water to the Arctic Ocean through the Fram Strait. The data set included 85 stratified vertical zooplankton samples (obtained from depths up to 1000 metres) covering two latitudinal sections (76°30’N and 79°N) located across the multi-path WSC system. The results indicate that the most important environmental variables shaping the zooplankton structural and functional diversity and standing stock variability are those associated with depth, whereas variables acting in the horizontal dimension are of lesser importance. Multivariate analysis of the zooplankton assemblages, together with different univariate descriptors of zooplankton diversity, clearly illustrated the segregation of zooplankton taxa in the vertical plane. The epipelagic zone (upper 200 m) hosted plentiful, Oithona similis-dominated assemblages with a high proportion of filter-feeding zooplankton. Although total zooplankton abundance declined in the mesopelagic zone (200–1000 m), zooplankton assemblages in that zone were more diverse and more evenly distributed, with high contributions from both herbivorous and carnivorous taxa. The vertical distribution of integrated biomass (mg DW m-2) indicated that the total zooplankton biomass in the epipelagic and mesopelagic zones was comparable. Environmental gradients acting in the horizontal plane, such as the ones associated with different ice cover and timing of the spring bloom, were reflected in the latitudinal variability in protist community structure and probably caused differences in succession in the zooplankton community. High abundances of Calanus finmarchicus in the WSC core branch suggest the existence of mechanisms advantageous for higher productivity or/and responsible for physical concentration of zooplankton. Our results indicate that regional hydrography plays a primary role in shaping zooplankton variability in the WSC on the way to the Arctic Ocean, with additional effects caused by biological factors related to seasonality in pelagic ecosystem development, resulting in regional differences in food availability or biological production between the continental slope and the deep ocean regions.
Highlights
Arctic amplification, caused by many factors operating on different time and space scales, is recognised as an integral characteristic of the global climate system [1]
Knowledge of the physical and biological spatial heterogeneity of the West Spitsbergen Current (WSC) en route to the Arctic Ocean through the Fram Strait is a basic requirement for assessing the impact of climate change on the Arctic ecosystems, and can be used to create various scenarios dealing with global warming
Full-depth hydrographic measurements at the fixed stations revealed that the core of Atlantic water (AW) (WSCc) over the Spitsbergen slope reached 600 m at the LAT section 76 ̊30’N (13 ̊00’-13 ̊ 30’E) and 500 m at the section 79 ̊N (8 ̊00’-8 ̊40’E, Fig 2)
Summary
Arctic amplification, caused by many factors operating on different time and space scales, is recognised as an integral characteristic of the global climate system [1]. The West Spitsbergen Current (WSC) provides the principal contribution of salt and sensible heat to the Arctic Ocean [4]. Knowledge of the physical and biological spatial heterogeneity of the WSC en route to the Arctic Ocean through the Fram Strait is a basic requirement for assessing the impact of climate change on the Arctic ecosystems, and can be used to create various scenarios dealing with global warming. The Atlantic water (AW) is transported into the Nordic Seas by two branches of the Norwegian Atlantic Current [5,6,7]. The warmer, more saline eastern branch, known as the Norwegian Atlantic Slope Current, bifurcates after passing Norway into the stream of the AW, entering the Barents Sea and the core of the West Spitsbergen Current (WSCc) [8]. The West Spitsbergen multi-path current system most likely highly influences the spatial biological heterogeneity of this region, especially in the pelagic realm
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