An 8-year time series of mesozooplankton fluxes in Kongsfjorden, Svalbard

Abstract

In Arctic regions, the food availability for epi-pelagic fauna is strictly influenced by environmental stressors, such as solar radiation, ice cover, glacial and watershed runoffs. This study presents an 8-year time-series (2010-2018) of mesozooplankton collected from an automatic sediment trap in the inner part of Kongsfjorden, Svalbard, at ~87m depth. The aim of this study is to observe the temporal variability in the abundance of epipelagic mesozooplankton species, collected as active flux (swimmers). Reference meteorological and hydrological data are also presented as environmental stressors, to evaluate possible relationships with zooplankton populations. A principal component analysis (PCA) applied to the dataset revealed that the physical and chemical characteristics of seawater affected the mesozooplankton abundance and composition. Collectively, this result highlighted the role of the thermohaline characteristics of the water column on the Copepods behavior, and the correlation between siliceous phytoplankton and Amphipods. Overall, the zooplankton within inner Kongsfjorden did not show a clear seasonal trend, suggesting their high adaptivity to extreme environmental conditions. Although the swimmer fluxes have decreased from 2013 onwards, an increase in community diversity has nevertheless been observed, probably due to copepods decline and subsequent higher food availability. Despite the decreasing magnitude of the zooplanktonic community over time, we recorded the intrusion of subarctic boreal species, such as Limacina retroversa, since 2016. The uniqueness of this dataset is an 8-year uninterrupted time series, which provides correlations between environmental and biological parameters in a poorly studied region. Under a warming Kongsfjorden scenario, with increasing submarine and watershed runoff, and the rapid Atlantification of the fjord, major changes in mesozooplankton communities are expected in the medium to long-term due to their adaptation to environmental changes and the introduction of alien species.