Zooplankton seasonal variability in Arctic fjord during cold and warm events – taxonomic and trait-based approaches (Kongsfjorden, Svalbard)

Abstract

Kongsfjorden, located on the west coast of Spitsbergen (79°N), lies at the boundary between Arctic and Atlantic water masses, making it an ideal site for studying the influence of environmental conditions on ecosystem dynamics and offering insights applicable to other Arctic regions. In this study, we describe the seasonal succession and interannual variability of the zooplankton community in Kongsfjorden in quantitative, taxonomic, and ecological terms, as observed during years with contrasting hydrographic conditions. The analysis is based on data collected in 2002, 2006, and 2007—years characterized by pronounced environmental differences, particularly in spring, with notable variation in seawater temperature and salinity. Zooplankton samples were collected from stations within the fjord and on the adjacent shelf using vertically stratified hauls with a Hydro-Bios Multi Plankton Sampler midi (180 μm mesh). Ecologically, the zooplankton community was analyzed using four traits—body size, feeding mode, spawning strategy, and transparency—allowing classification of 115 taxa into ten functional groups. Across all seasons, zooplankton biomass was consistently dominated by non-gelatinous, medium-sized, free-spawning forms. A clear seasonal shift in functional composition was observed, from current feeders in spring to ambush feeders in autumn, reflecting changes in food availability and trophic dynamics. Trait-based patterns proved more stable than taxonomic composition and more effectively captured key aspects of zooplankton functional roles in ecosystem processes, including trophic interactions, carbon export, and pelago–benthic coupling. Although the data reflect conditions from nearly two decades ago, they represent both cold and warm hydrographic states and remain ecologically relevant. Our findings highlight the sensitivity of Arctic zooplankton communities to early-season hydrography and bloom composition, and underscore the value of trait-based approaches for detecting structural shifts and anticipating ecosystem responses under ongoing Arctic Atlantification.