The autumn plankton community of an Arctic fjord: impact of temperature and salinity on the functional response of two copepod species “to watch”

Abstract Here, we describe the plankton community of a freshwater impacted Arctic fjord, Kangerluarsuk Ungalleq, west Greenland, during early autumn 2023. Small phytoplankton (< 10 μm) dominated the autotrophs, and protozooplankton (ciliates and dinoflagellates) dominated the grazers, accounting for 98% of zooplankton biomass in the upper part of the water column. Protozooplankton was mainly constituted by aloricate ciliates, while the cyclopoid Oithona similis was the most abundant copepod. Calanus spp. contributed most to copepod biomass, especially in the cold, salty bottom water inside the midway sill. We also investigated the impact of temperature rise and salinity decrease on two copepod species from the fjord, Acartia longiremis and Eurytemora americana, which we consider potential benefactors of climate change. E. americana is a non-indigenous species in Greenland, and this was, to our knowledge, the first observation. Neither of the species altered their functional response (fecal pellet production in relation to food concentration) in low salinity, which indicate high freshwater tolerance. Temperature had a large effect on A. longiremis’s functional response, where the Q10 for maximum ingestion was 8.6. In contrast, E. americana showed a much weaker response, with a Q10 for maximum ingestion of 1.6. Our results suggest that A. longiremis could benefit from temperature rise if food is sufficient, while E. americana does not pose a threat to the native Arctic copepod community.