Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance

Abstract

The Arctic Ocean is a region particularly prone to ongoing ocean acidification (OA) and climate-driven changes. The influence of these changes on Arctic phytoplankton assemblages, however, remains poorly understood. In order to understand how OA and enhanced irradiances (e.g., resulting from sea-ice retreat) will alter the species composition, primary production, and ecophysiology of Arctic phytoplankton, we conducted an incubation experiment with an assemblage from Baffin Bay (71°N, 68°W) under different carbonate chemistry and irradiance regimes. Seawater was collected from just below the deep Chl a maximum, and the resident phytoplankton were exposed to 380 and 1000 latm pCO 2 at both 15 and 35% incident irradiance. On-deck incubations, in which temperatures were 6°C above in situ conditions, were monitored for phytoplankton growth, biomass stoichiometry, net primary production, photo-physiology, and taxonomic composition. During the 8-day experiment, taxonomic diversity decreased and the diatom Chaetoceros socialis became increasingly dominant irrespective of light or CO 2 levels. We found no statistically significant effects from either higher CO 2 or light on physiological properties of phytoplankton during the experiment. We did, however, observe an initial 2-day stress response in all treatments, and slight photo-physiological responses to higher CO 2 and light during the first five days of the incubation. Our results thus indicate high resistance of Arctic phytoplankton to OA and enhanced irradiance levels, challenging the commonly predicted stimulatory effects of enhanced CO 2 and light availability for primary production.

Impacts of Temperature, CO2, and Salinity on Phytoplankton Community Composition in the Western Arctic Ocean

“…than in the MR15-exp., suggesting that diversity is an important factor in resisting or buffering the effects of environmental perturbations such as temperature in phytoplankton community composition. Previous studies suggested that intraspecific variability of sensitivity to high CO 2 conditions is one of the important factors that determines the stability of phytoplankton productivity (Hoppe et al, 2017(Hoppe et al, , 2018cWolf et al, 2018). In this study, C. closterium appeared in both experiments.…”

“…Although numerous studies from the previous decades have reported temperature and/or CO 2 manipulation experiments (Yoshimura et al, 2014;Schulz et al, 2017 and references therein), few have focused on the Arctic Ocean. A few experiments have been conducted in the eastern Arctic Ocean, but the results were inconsistent with one another Holding et al, 2015;Hoppe et al, 2017;Wolf et al, 2018). For example, Holding et al (2015) reported an enhancement of primary productivity under increased CO 2 levels, whereas Hoppe et al (2017) did not.…”

“…A few experiments have been conducted in the eastern Arctic Ocean, but the results were inconsistent with one another Holding et al, 2015;Hoppe et al, 2017;Wolf et al, 2018). For example, Holding et al (2015) reported an enhancement of primary productivity under increased CO 2 levels, whereas Hoppe et al (2017) did not. In terms of community composition, eukaryotic picophytoplankton (PicoE) tended to dominate under the higher CO 2 levels .…”

“…In terms of community composition, eukaryotic picophytoplankton (PicoE) tended to dominate under the higher CO 2 levels . Species shifts occurred between different diatom species that were functionally similar (Hoppe et al, 2017); the lack of change in species composition was probably caused by intraspecific variability in the responses of dominant diatom species to CO 2 variations (Wolf et al, 2018).…”

Reply to RC2

“…To our knowledge, this is the first report of bSiO 2 production data of the natural diatom community in this sector of the Arctic. Other studies have reported ρ data in the subarctic Atlantic Ocean (Brown et al, 2003;Kristiansen et al, 2000;Allen et al, 2005) ∼ 10-20 • latitude south of our study region or in Baffin Bay (Hoppe et al, 2018;Tremblay et al, 2002). However, the Hoppe et al (2018) study only includes ρ measured after a 24 h manipulation experiment and only at one site and depth near the Clyde River just east of Nunavut (Canada); no data are reported for the ambient conditions, and the measurements from Tremblay et al (2002) are based on net changes in standing stocks instead of gross bSiO 2 production.…”