Metabolic Responses of Subtropical Microplankton After a Simulated Deep-Water Upwelling Event Suggest a Possible Dominance of Mixotrophy Under Increasing CO2 Levels

• Published in: Frontiers in Marine Science
• Main Authors: Tames-Espinosa, Mayte, Martínez, Ico, Romero-Kutzner, Vanesa, Coca, Josep, Algueró-Muñiz, María, Horn, Henriette G., Ludwig, Andrea, Taucher, Jan, Bach, Lennart, Riebesell, Ulf, Packard, Theodore T., Gómez, May
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers 2020
• Subjects: North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/49784/; https://oceanrep.geomar.de/id/eprint/49784/1/fmars-07-00307.pdf; https://oceanrep.geomar.de/id/eprint/49784/2/Data_Sheet_1_Metabolic%20Responses%20of%20Subtropical%20Microplankton%20After%20a%20Simulated%20Deep-Water%20Upwelling%20Event%20Suggest%20a%20Possible%20Dominance%20of%20Mixotrophy%20.PDF; https://doi.org/10.3389/fmars.2020.00307

In the autumn of 2014, nine large mesocosms were deployed in the oligotrophic subtropical North-Atlantic coastal waters off Gran Canaria (Spain). Their deployment was designed to address the acidification effects of CO2 levels from 400 to 1,400 mu atm, on a plankton community experiencing upwelling of nutrient-rich deep water. Among other parameters, chlorophyll a (chl-a), potential respiration (Phi), and biomass in terms of particulate protein (B) were measured in the microplankton community (0.7-50.0 mu m) during an oligotrophic phase (Phase I), a phytoplankton-bloom phase (Phase II), and a post-bloom phase (Phase III). Here, we explore the use of the Phi/chl-a ratio in monitoring shifts in the microplankton community composition and its metabolism. Phi/chl-a values below 2.5 mu L O-2 h(-1) (mu g chl-a)(-1) indicated a community dominated by photoautotrophs. When Phi/chl-a ranged higher, between 2.5 and 7.0 mu L O-2 h(-1) (pg chl-a)(-1) , it indicated a mixed community of phytoplankton, microzooplankton and heterotrophic prokaryotes. When Phi/chl-a rose above 7.0 mu L O-2 h(-1) (mu g chl-a)(-1), it indicated a community where microzooplankton proliferated (>10.0 mu L O-2 h(-1) (mu g chl-a)(-1)), because heterotrophic dinoflagellates bloomed. The first derivative of B, as a function of time (dB/dt), indicates the rate of protein build-up when positive and the rate of protein loss, when negative. It revealed that the maximum increase in particulate protein (biomass) occurred between 1 and 2 days before the chl-a peak. A day after this peak, the trough revealed the maximum net biomass loss. This analysis did not detect significant changes in particulate protein, neither in Phase I nor in Phase III. Integral analysis of Phi/chl-a and B, over the duration of each phase, for each mesocosm, reflected a positive relationship between 4) and pCO(2) during Phase II [alpha = 230.10-5 mu L O-2 h(-1) L-1 (patm CO2)(-1) (phase-day)(-1), R-2 = 0.30] and between chl-a and pCO(2) during Phase III [alpha = 100.10(-5) Ag chl-a ...