Contrasting shallow near-bottom zooplankton assemblage-flux pathways under different hydrographic conditions in Kongsfjorden

Abstract

Zooplankton variability in Arctic fjords is commonly assessed in the water column but remains less resolved in shallow coastal near-bottom habitats. Here, we analyzed two late spring–summer sediment-trap deployments conducted in 2018 and 2019 at a single shallow coastal site near Ny-Ålesund harbour, Kongsfjorden, Svalbard, together with trap-depth temperature–salinity records, treating trap-collected zooplankton as local, interval-averaged assemblage fluxes. In each deployment, four hydrographic stages and four data-derived zooplankton-flux phases were identified, with contrasting temporal patterns in hydrographic conditions and zooplankton assemblage composition. Trap-depth hydrographic conditions showed progressive warming and freshening in 2018, whereas 2019 was warmer and generally more saline during the early and middle deployment before freshening later. The 2018 zooplankton sequence was meroplankton-rich, with prominent barnacle and polychaete larval contributions followed by a short copepod/Calanus pulse. In 2019, a sustained Calanus finmarchicus-dominated sequence shifted from younger copepodites earlier to greater C4–C5 contributions later. Correlation and multivariate analyses showed that zooplankton assemblage variation was associated with trap-depth temperature–salinity conditions, while zooplankton-flux phase boundaries did not consistently coincide with hydrographic-stage boundaries. Together, these hydrographic and biological contrasts were interpreted as two conceptual assemblage-flux pathways: one meroplankton-rich in 2018 and the other C. finmarchicus-dominated in 2019. These pathways provide a framework for interpreting shallow near-bottom zooplankton variability and for testing whether comparable patterns recur across seasons, years and sites. This study also shows that sediment traps deployed in shallow coastal waters can provide a time-integrated perspective on local zooplankton variability.