Ocean acidification reduces growth and grazing impact of Antarctic heterotrophic nanoflagellates

• Published in: Biogeosciences
• Main Authors: S. Deppeler, K. G. Schulz, A. Hancock, P. Pascoe, J. McKinlay, A. Davidson
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Antarctic; East Antarctica; Prydz Bay; Southern Ocean; Antarc*; Antarctica; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-17-4153-2020; https://doaj.org/article/a4007cb9f0764001b43957bc8805cac6

High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO 2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing f CO 2 on the growth of heterotrophic nanoflagellates (HNFs), nano- and picophytoplankton, and prokaryotes (heterotrophic Bacteria and Archaea) in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO 2 levels ≥634 µ atm, HNF abundance was reduced, coinciding with increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNFs. Nanophytoplankton abundance was elevated in the 634 µ atm treatment, suggesting that moderate increases in CO 2 may stimulate growth. The taxonomic and morphological differences in CO 2 tolerance we observed are likely to favour dominance of microbial communities by prokaryotes, nanophytoplankton, and picophytoplankton. Such changes in predator–prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean, intensifying organic-matter recycling in surface waters; reducing vertical carbon flux; and reducing the quality, quantity, and availability of food for higher trophic levels.