Abstract

The acidification of the oceans could potentially alter marine plankton communities with consequences for ecosystem functioning. While several studies have investigated effects of ocean acidification on communities using traditional methods, few have used genetic analyses. Here, we use community barcoding to assess the impact of ocean acidification on the composition of a coastal plankton community in a large scale, in situ, long-term mesocosm experiment. High-throughput sequencing resulted in the identification of a wide range of planktonic taxa (Alveolata, Cryptophyta, Haptophyceae, Fungi, Metazoa, Hydrozoa, Rhizaria, Straminipila, Chlorophyta). Analyses based on predicted operational taxonomical units as well as taxonomical compositions revealed no differences between communities in high CO2 mesocosms (~ 760 μatm) and those exposed to present-day CO2 conditions. Observed shifts in the planktonic community composition were mainly related to seasonal changes in temperature and nutrients. Furthermore, based on our investigations, the elevated CO2 did not affect the intraspecific diversity of the most common mesozooplankter, the calanoid copepod Pseudocalanus acuspes. Nevertheless, accompanying studies found temporary effects attributed to a raise in CO2. Differences in taxa composition between the CO2 treatments could, however, only be observed in a specific period of the experiment. Based on our genetic investigations, no compositional long-term shifts of the plankton communities exposed to elevated CO2 conditions were observed. Thus, we conclude that the compositions of planktonic communities, especially those in coastal areas, remain rather unaffected by increased CO2.

Highlights

  • Enhanced atmospheric CO2 concentrations result in an increase in surface ocean pCO2 with a subsequent decrease in pH

  • Based on the community barcoding data elevated CO2 had no significant effect on the relative abundance or compilation of coastal planktonic taxa during a winter-to-summer succession in the mesocosms investigated in this field experiment

  • The resilience of coastal plankton communities towards future ocean acidification (OA) conditions was demonstrated in earlier large scale mesocosm field and indoor studies [9,10,11,12,13, 57, 58]

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Summary

Introduction

Enhanced atmospheric CO2 concentrations result in an increase in surface ocean pCO2 with a subsequent decrease in pH. Several studies have investigated the effects of ocean acidification (OA) on marine biota under laboratory and field conditions. Direct and indirect effects of OA on single species, which retard development [2], reduce reproduction [3, 4] and survival [5], may alter community structures [6] and thereby impact the food web [7, 8]. Investigations during large-scale mesocosm field studies in Espegrend (Bergen, Norway) and Kongsfjorden (Ny-Ålesund, Svalbard) showed an overall resilience of plankton communities (bacteria, phytoplankton, micro- and mesozooplankton) towards enhanced CO2 concentrations, whereby observed biological responses were largely depending on temperature and nutrient availability [9,10,11,12,13]

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