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Metabolic responses of subtropical microplankton after a simulated deep-water upwelling event suggest a possible dominance of mixotrophy under increasing CO2 levels

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Tames-Espinosa, M, Martinez, I, Romero-Kutzner, V, Coca, J, Alguero-Muniz, M, Horn, HG, Ludwig, A, Taucher, J, Bach, L ORCID: 0000-0003-0202-3671, Riebesell, U, Packard, TT and Gomez, M 2020 , 'Metabolic responses of subtropical microplankton after a simulated deep-water upwelling event suggest a possible dominance of mixotrophy under increasing CO2 levels' , Frontiers in Marine Science, vol. 7, no. MAY , pp. 1-15 , doi: 10.3389/fmars.2020.00307.

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Abstract

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 μatm, on a plankton community experiencing upwelling of nutrient-rich deep water. Among other parameters, chlorophyll a (chl-a), potential respiration (Φ), and biomass in terms of particulate protein (B) were measured in the microplankton community (0.7–50.0 μm) 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 Φ/chl-a ratio in monitoring shifts in the microplankton community composition and its metabolism. Φ/chl-a values below 2.5 μL O2 h−1 (μg chl-a)−1 indicated a community dominated by photoautotrophs. When Φ/chl-a ranged higher, between 2.5 and 7.0 μL O2 h−1 (μg chl-a)−1, it indicated a mixed community of phytoplankton, microzooplankton and heterotrophic prokaryotes. When Φ/chl-a rose above 7.0 μL O2 h−1 (μg chl-a)−1, it indicated a community where microzooplankton proliferated (>10.0 μL O2 h−1 (μg 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 Φ, chl-a and B, over the duration of each phase, for each mesocosm, reflected a positive relationship between Φ and pCO2 during Phase II [α = 230·10−5 μL O2 h−1 L−1 (μatm CO2)−1 (phase-day)−1, R2 = 0.30] and between chl-a and pCO2 during Phase III [α = 100·10−5 μg chl-a L−1 (μ atmCO2)−1 (phase-day)−1, R2 = 0.84]. At the end of Phase II, a harmful algal species (HAS), Vicicitus globosus, bloomed in the high pCO2 mesocosms. In these mesocosms, microzooplankton did not proliferate, and chl-a retention time in the water column increased. In these V. globosus-disrupted communities, the Φ/chl-a ratio [4.1 ± 1.5 μL O2 h−1 (μg chl-a)−1] was more similar to the Φ/chl-a ratio in a mixed plankton community than to a photoautotroph-dominated one.

Item Type: Article
Authors/Creators:Tames-Espinosa, M and Martinez, I and Romero-Kutzner, V and Coca, J and Alguero-Muniz, M and Horn, HG and Ludwig, A and Taucher, J and Bach, L and Riebesell, U and Packard, TT and Gomez, M
Keywords: mixotrophy, phytoplankton, ocean acidification, mesocosms, nutrient fertilization, subtropical North-Atlantic, potential respiration, plankton metabolism
Journal or Publication Title: Frontiers in Marine Science
Publisher: Frontiers Research Foundation
ISSN: 2296-7745
DOI / ID Number: 10.3389/fmars.2020.00307
Copyright Information:

Copyright 2020 2020 Tames-Espinosa, Martínez, Romero-Kutzner, Coca, Algueró-Muñiz, Horn, Ludwig, Taucher, Bach, Riebesell, Packard and Gómez. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

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