The Influence of pCO2-Driven Ocean Acidification on Open Ocean Bacterial Communities during A Short-Term Microcosm Experiment in the Eastern Tropical South Pacific (ETSP) off Northern Chile.

Paulina Aguayo,Víctor L Campos,Francisca Olivares,Osvaldo Ulloa,Cristian A Vargas,Carlos Henríquez,Rodrigo De Ia Iglesia

doi:10.3390/microorganisms8121924

Abstract

Due to the increasing anthropogenic CO2 emissions, Ocean Acidification (OA) is progressing rapidly around the world. Despite the major role that microorganisms play on the marine biogeochemical cycling and ecosystem functioning, the response of bacterial communities upon OA scenarios is still not well understood. Here, we have conducted a detailed characterization of the composition and relative abundance of bacterial communities in the water column of an open-ocean station in the Eastern Tropical South Pacific (ETSP) off northern Chile and their interactions with environmental factors. In addition, through a short-term microcosm experiment, we have assessed the effect of low pH/high pCO2 conditions over the abundance and genetic diversity of bacterial communities. Our results evidence a clear partitioning of community composition that could be attributed mostly to dissolved oxygen. However, our experimental approach demonstrated that low pH/high pCO2 conditions might modify the structure of the bacterial community, evidencing that small changes in pH may impact significantly the abundance and diversity of key microorganisms. This study constitutes a first step aiming to provide insight about the influence of changing carbonate chemistry conditions on natural bacterial communities and to shed light on the potential impact of OA in biogeochemical cycles on the ETSP region.

Highlights

Little is known on how bacterial communities in the surface open ocean might respond to future changes in pCO2 and pH conditions [1]
We evaluated the response of surface bacterial communities to potential Ocean Acidification (OA) scenarios by using on-board short-term microcosm pCO2–perturbation experiments
The vertical distribution of pCO2 showed an opposite pattern to that observed for pHT, whereas the total alkalinity (AT) showed a slow decrease below 50 m to the deepest layer sampled during this study

Summary

Introduction

Little is known on how bacterial communities in the surface open ocean might respond to future changes in pCO2 and pH conditions [1]. The ocean has partially absorbed a significant fraction of the anthropogenic atmospheric CO2 emissions, this has come at the expense of altering carbon chemistry on the global ocean, disturbing its delicate geochemical balance [2]. This disruption of carbonate chemistry processes is known collectively as Ocean Acidification (OA) [3]. This disruption by the net effect of CO2 dissolution in the ocean causes an increase of hydrogen and bicarbonate ion concentration, altering seawater pH, and decreasing carbonate ions [4], which has profound consequences for marine biodiversity and ecosystem functioning in coastal and open ocean waters [5,6]. Recent studies suggest that contemporary evolution could support maintaining the functionality of microbial processes in the ocean in the face of global change [13,14]

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Discussion

Conclusion