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

Tames-Espinosa, M. et al. (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, 7, 307. (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:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Alguero-Muniz, Dr Maria
Authors: Tames-Espinosa, M., Martínez, I., Romero-Kutzner, V., Coca, J., Algueró-Muñiz, M., Horn, H. G., Ludwig, A., Taucher, J., Bach, L., Riebesell, U., Packard, T. T., and Gómez, M.
College/School:College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Journal Name:Frontiers in Marine Science
Publisher:Frontiers Media
ISSN:2296-7745
ISSN (Online):2296-7745
Copyright Holders:Copyright © 2020 Tames-Espinosa, Martínez, Romero-Kutzner, Coca, AlgueróMuñiz, Horn, Ludwig, Taucher, Bach, Riebesell, Packard and Gómez
First Published:First published in Frontiers in Marine Science 7: 307
Publisher Policy:Reproduced under a Creative Commons License

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