The interplay between predatory chaetognaths and zooplankton community in a high Arctic fjord.

In the marine environment, chaetognaths are among the major predators of zooplankton. The most common Chaetognatha species in the Arctic coastal waters are Parasagitta elegans and Eukrohnia hamata. Their distribution and size structure and potential predatory impact on the zooplankton community were analyzed in Isfjorden (Svalbard Archipelago). Parasagitta elegans dominated in terms of biomass (1.5 mg DM ∙ m−3) over E. hamata (0.09 mg DM ∙ m−3), and the clear pattern of chaetognaths' size distribution was noticed: smaller individuals occurred in the upper water layers, while larger ones were observed near the fjords' bottom. Based on Redundancy Analysis (RDA) followed by variation partitioning, the zooplankton community was influenced by environmental variables (36.6%) and by chaetognaths (16.6%), while the joint impact for both groups of these predictors was 46.6%. Both increasing temperature and P. elegans influenced medium-sized and small copepods (e.g., Calanus finmarchicus, Oithona similis), pteropods, and meroplankton larvae (upper layers), while E. hamata was related to larger copepods (e.g., Calanus hyperboreus , Metridia longa) at greater depths. The study showed different predation pressure of P. elegans and E. hamata in the Arctic fjord and revealed complex interactions within the zooplankton community and marine environment. • Environment and chaetognaths had influenced the zooplankton structure. • Cheatognaths' predation influence on selected zooplankton species was confirmed. • Depending on size class, chaetognaths influenced both large and small copepods. • The zooplankton biomass in the water column decreased with depth. • Atlantification may affect the occurrence and biomass of Calanus glacialis. [ABSTRACT FROM AUTHOR]