MEPS 569:89-102 (2017)  -  DOI: https://doi.org/10.3354/meps12072

ABSTRACT: Recent rapid climate change in the Arctic has profound effects on polar marine ecosystems. In this study, we used time-for-space substitution to evaluate possible plankton responses to sea ice reduction and rising sea temperatures.  The microbial food web was examined across a natural temperature gradient in the Barents Sea and adjacent waters (70-78.5°N; -1.8 to 8.6°C) during different seasonal phases. On average, grazers consumed 92% of phytoplankton daily production (57 and >100% in the ice-covered Arctic and the North Atlantic-influenced open waters, respectively). Microzooplankton biomass and production peaked on the Atlantic side of the Polar Front, where mixotrophic ciliates were responsible for up to 49% of total chlorophyll a and a very efficient energy transfer (community production to ingestion ratios of 38 to >100%). Despite pronounced seasonal and latitudinal shifts in plankton composition, several key microbial food web parameters increased linearly with temperature, including bacterial biomass, microzooplankton herbivory rate and its relative impact, and the proportion of smaller and heterotrophic cells in microzooplankton. Overall, the microbial food web changed gradually across the temperature gradient and was characterized by tight trophic linkages among its constituents within the dominant water masses.

KEY WORDS: Barents Sea · Microzooplankton · Herbivory · Bacteria · Secondary production · Dilution assay · Temperature effect