Net community production of Arctic mixed kelp communities in response to warming, freshening, and attenuated light: a mesocosm study as per minute record

Arctic marine ecosystems are experiencing rapid environmental changes with respect to warming, ice melt, and terrestrial run-off. The effects of these perturbations can act as multi-stressors where warming sea seawater, in combination with freshening from ice melt, and increased turbidity from terrestrial run-off affect benthic community structure and function. To examine the effects of warming, freshening, and turbidity on habitat forming macroalgae, we conducted a 2-month long ex situ experiment on mixed Arctic kelp communities in Ny-Ålesund, Svalbard from 03/07/2021 - 26/08/2021. Three experimental conditions (with 3x replicates) were tested against a dynamic real-time control where temperature was increased by + 3.3 and + 5.3 °C, salinity was reduced by ~ 4 and ~ 5, and irradiance was statically attenuated by ~ 25 and 40 % in 2 treatments. The third treatment was only warmed by + 5.3 °C from the control. In each 1 m³ mesocosm, oxygen (% O2), temperature, salinity, and photosynthetically active radiation (PAR) were continuously monitored. Mixed kelp communities comprised a biomass of ~ 4 kg fw (fresh weight) and ~ 500 g fw of small fauna. Weekly incubations were performed to calculate net community productivity (NCP) and used to estimate kelp benthic metabolism. We determined non-significant differences across treatments and provide NCP rates for mixed kelp communities in the Arctic.