Coccolithophore community response along a natural CO2 gradient off Methana (SW Saronikos Gulf, Greece, NE Mediterranean).

Maria V Triantaphyllou,Boris-Theofanis Karatsolis,Elisavet Skampa,Olga Koukousioura,Karl-Heinz Baumann,Margarita D Dimiza,Paraskevi Nomikou,Nele M Vollmar,Stella Psarra,Anna Katsigera,Pierros Patoucheas,Evangelia Krasakopoulou

doi:10.1371/journal.pone.0200012

Abstract

A natural pH gradient caused by marine CO2 seeps off the Methana peninsula (Saronikos Gulf, eastern Peloponnese peninsula) was used as a natural laboratory to assess potential effects of ocean acidification on coccolithophores. Coccolithophore communities were therefore investigated in plankton samples collected during September 2011, September 2016 and March 2017. The recorded cell concentrations were up to ~50 x103 cells/l, with a high Shannon index of up to 2.8, along a pH gradient from 7.61 to 8.18, with values being occasionally <7. Numerous holococcolithophore species represented 60–90% of the surface water assemblages in most samples during September samplings. Emiliania huxleyi was present only in low relative abundances in September samples, but it dominated in March assemblages. Neither malformed nor corroded coccolithophores were documented. Changes in the community structure can possibly be related to increased temperatures, while the overall trend associates low pH values with high cell densities. Our preliminary results indicate that in long-termed acidified, warm and stratified conditions, the study of the total coccolithophore assemblage may prove useful to recognize the intercommunity variability, which favors the increment of lightly calcified species such as holococcolithophores.

Highlights

The cumulative emissions in anthropogenic CO2 from 1870 to 2014 totaled about 545 GtC; almost half of these emissions remain in the atmosphere and increase the potential to enhance climate change [1]
Assuming that AT remains relatively constant in the area and using our pH, salinity, temperature and nutrients data, we did a rough estimation of the saturation
Assemblages of living coccolithophores were investigated off Methana, eastern Peloponnese peninsula (Greece), along a pH gradient formed by natural CO2 seeps

Summary

Introduction

The cumulative emissions in anthropogenic CO2 from 1870 to 2014 totaled about 545 GtC; almost half of these emissions remain in the atmosphere and increase the potential to enhance climate change [1]. The oceans absorb approximately 30% of the atmospheric CO2 produced by anthropogenic activities [1,2,3,4]. The concentration of bicarbonate ions is increasing; causing simultaneous reduction in carbonate ions, decline of ocean pH and lowering of the calcium carbonate saturation state (O) of both calcite and aragonite [e.g., 1, 2, 5, 6]. During the last 200 years, surface ocean pH has fallen almost 0.1 units to a current day global average of approximately 8.2 [7]. The associated ocean acidification with surface pH.

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Conclusion