Seawater carbonate chemistry and plankton community structure during a winter-tosummer succession

• Main Authors: Taucher, Jan, Haunost, Mathias, Boxhammer, Tim, Bach, Lennart Thomas, Algueró-Muñiz, Maria, Riebesell, Ulf
• Format: Dataset
• Language: English
• Published: PANGAEA 2023
• Subjects: Alkalinity; total; Aragonite saturation state; Bicarbonate ion; Calcite saturation state; Calculated; Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; Community composition and diversity; Coulometric titration; Day of experiment; Entire community; Equivalent spherical diameter; Event label; Field experiment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Gullmar Fjord; Skagerrak; Sweden; Hand-operated CTD (Sea&Sun Technology; CTD 60M); KOSMOS_2013_Mesocosm-M1; KOSMOS_2013_Mesocosm-M10; KOSMOS_2013_Mesocosm-M2; KOSMOS_2013_Mesocosm-M3; KOSMOS_2013_Mesocosm-M4; KOSMOS_2013_Mesocosm-M5; KOSMOS_2013_Mesocosm-M6; KOSMOS_2013_Mesocosm-M7; KOSMOS_2013_Mesocosm-M8; KOSMOS_2013_Mesocosm-M9; KOSMOS 2013; MESO; Mesocosm experiment; Mesocosm or benthocosm; North Atlantic; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Particle concentration; Particle size spectrum; Pelagos; pH; Phosphate; Plankton; Ocean acidification; Copepods
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.958012; https://doi.org/10.1594/PANGAEA.958012

Plankton communities play a key role in the marine food web and are expected to be highly sensitive to ongoing environmental change. Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. These changes–summarized by the term ocean acidification (OA)–can significantly affect the physiology of planktonic organisms. However, studies on the response of entire plankton communities to OA, which also include indirect effects via food-web interactions, are still relatively rare. Thus, it is presently unclear how OA could affect the functioning of entire ecosystems and biogeochemical element cycles. In this study, we report from a long-term in situ mesocosm experiment, where we investigated the response of natural plankton communities in temperate waters (Gullmarfjord, Sweden) to elevated CO2 concentrations and OA as expected for the end of the century (~760 μatm pCO2). Based on a plankton-imaging approach, we examined size structure, community composition and food web characteristics of the whole plankton assemblage, ranging from picoplankton to mesozooplankton, during an entire winter-to-summer succession. The plankton imaging system revealed pronounced temporal changes in the size structure of the copepod community over the course of the plankton bloom. The observed shift towards smaller individuals resulted in an overall decrease of copepod biomass by 25%, despite increasing numerical abundances. Furthermore, we observed distinct effects of elevated CO2 on biomass and size structure of the entire plankton community. Notably, the biomass of copepods, dominated by Pseudocalanus acuspes, displayed a tendency towards elevated biomass by up to 30–40% under simulated ocean acidification. This effect was significant for certain copepod size classes and was most likely driven by CO2-stimulated responses of primary producers and a complex interplay of trophic interactions that allowed this CO2 effect to propagate up the food web. Such ...