Variations in the structural and functional diversity of zooplankton over vertical and horizontal environmental gradients en route to the Arctic Ocean through the Fram Strait

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.

Dynamics of Calanus Copepodite Structure during Little Auks’ Breeding Seasons in Two Different Svalbard Locations

“…Such similarity in the Calanus age structure observed in Rijpfjorden and Hornsund indicates a coincident timing of reproductive events and its synchrony with ice algae bloom in April and phytoplankton bloom in July [96]. In addition, the presence of early copepodite stages in all the studied periods (this study) might suggest continuous reproduction, or at least, the presence of more than one generation of Calanus, which is likely in high latitudes according to several new studies [20,65,97]. In Kongsfjorden, the trend of a gradual population development was observed in this work only in 2015.…”

Seasonal Variation in Transport of Zooplankton Into the Arctic Basin Through the Atlantic Gateway, Fram Strait

“…Over the last decades this AW inflow has become warmer (Beszczynska-Möller et al, 2012), and it has been identified as the main mediator of climate change in the Arctic marine environment (Spielhagen et al, 2011;Polyakov et al, 2012;Onarheim et al, 2014). In addition to heat, the AW current transports phytoplankton (Hegseth and Sundfjord, 2008;Metfies et al, 2016) and zooplankton of Atlantic origin, and with different functional roles (Kosobokova and Hirche, 2009;Kraft et al, 2013;Gluchowska et al, 2017b). Changes in ecosystem structure at lower latitudes are thus advected into the Arctic Basin and affect productivity and carbon cycling (Hunt et al, 2016).…”

Summer Mesozooplankton Biomass Distribution in the West Spitsbergen Current (2001–2014)

“…For Arctic standards, this data set is unique due to its spatial and temporal coverage. While these data have been used to analyze how environmental variables shape the distribution of key Calanus species , zooplankton community structure (Weydmann et al, 2014;Gluchowska et al, 2017a), zooplankton structural and functional diversity (Gluchowska et al, 2017b), and population development of Calanus finmarchicus (Gluchowska et al, 2017a;Weydmann et al, 2018), the spatial and temporal variability in the zooplankton community has not yet been fully explored.…”