Fig 1.
A. Map of the central Aegean Sea (NE Mediterranean) with sampling sites visited in the present study; Methana represents the western end of the Aegean Volcanic Arc. Image resource: NASA Worldview. The inlet map presents the dominant tectonic structure of the Aegean Sea domain [48]. B. Bathymetry and hydrography of Saronikos Gulf. Bathymetry data are provided by HCMR (Hellenic Centre for Marine Research). The map was designed with ArcGiS software (ESRI) v.10.4. Hydrographic data are redrawn from [46]. C. Sample location around Methana peninsula. Image resource: NASA Worldview.
Table 1.
Stations’ location, sampling dates, physicochemical parameters, total coccolithophore density (cells l-1) resulting from both inverted microscopy and Scanning Electron Microscopy techniques and coccolithophore diversity (H’) based on SEM countings.
Table 2.
Seawater carbonate chemistry, average nutrient concentrations and total chl-a values in the sampling sites.
Fig 2.
The structure of plankton community.
Abundance (cells l-1) of the major plankton groups Dinophyceae, Bacillariophyceae and the Coccolithophores component, during the two sampling periods.
Table 3.
Coccolithophore community structure.
Hetrococcolithophore and holococcolithophore densities in the different sampling periods and the different sampling sites in Methana and Andros Island.
Fig 3.
Coccolithophore species composition.
Relative abundance of coccolithophore species during September 2011 sampling, September 2016 and March 2017 samplings. Image resource: NASA Worldview.
Fig 4.
Coccolithophore community structure.
Heterococcolithophore-holococcolithophore ratios in the sampling sites during the different sampling periods.
Fig 5.
Coccolithophores of Methana acidified environments.
1. E. huxleyi, P1-5 m, September 2016 (Ωmin<1). 2. E. huxleyi, P2-5 m, March 2017 (pH<8). 3. Pontosphaera syracusana, P2-2 m, March 2017. 4. Syracosphaera halldalii, P1-2 m, September 2016 (Ωmin<1). 5. Syracosphaera ossa, P1-2 m, September 2016. 6. Algyrosphaera robusta HOL, P1-2 m, September 2016 (Ωmin<1). 7. Syracosphaera mediterranea, P1-2 m, September 2016 Ωmin<1). 8. Rhabdosphaera clavigera, P1-2 m, September 2016 (Ωmin<1). 9. Algyrosphaera robusta, P1-2 m, September 2016 (Ωmin<1). 10. Syracolithus ponticuliferus, P1-2 m, September 2016 (Ωmin<1). 11. Algyrosphaera robusta HOL, P1-2 m, September 2016 (Ωmin<1). 12. Syracosphaera mediterranea HOL wettsteinii type, P1-2 m, September 2016 (Ωmin<1).
Fig 6.
Coccolithophore corroded specimens in Methana acidified environments (Ω<1).
1. Rhabdosphaera clavigera, P2-2 m, September 2016. 2. Syracosphaera pulchra, P2-8 m, September 2011. 3. Syracosphaera pulchra, P2-20 m, September 2011. 4. Syracosphaera mediterranea HOL (hellenica), P1-20 m, September 2011. 5. Emiliania huxleyi, P1-2 m, September 2016. 6. Homozygosphaera arethusae, P1-2 m, September 2016.
Fig 7.
Corellation of various coccolithophore groups and coccolithophore diversity with in situ pH data.
Holococcolithophores and particularly A. robusta HOL showed a clear increasing trend with lower pH during the warm period (September 2016), forcing diversity (H’) to display an opposite pattern. (obtained p values below 0.05 indicate statistically significant correlation at the 95% confidence level).