Is coccolithophore distribution in the Mediterranean Sea related to seawater carbonate chemistry?

anglais. Research article

anglais. The Mediterranean Sea is considered a “hot spot”for climate change, being characterized by oligotrophicto ultra-oligotrophic waters and rapidly increasing seasurfacetemperature and changing carbonate chemistry. Coccolithophoresare considered a dominant phytoplankton groupin these waters. As marine calcifying organisms they areexpected to respond to the ongoing changes in seawatercarbonate chemistry. We provide here a description of thespringtime coccolithophore distribution in the MediterraneanSea and relate this to a broad set of in situ-measured environmentalvariables. Samples were taken during the R/VMeteor (M84/3) oceanographic cruise in April 2011, between0 and 100m water depth from 28 stations. Total diatomand silicoflagellate cell concentrations are also presented.Our results highlight the importance of seawatercarbonate chemistry, especially [CO2􀀀� 3 ] but also [PO3􀀀� 4 ] inunraveling the distribution of heterococcolithophores, themost abundant coccolithophore life phase. Holo- and heterococcolithophoresrespond differently to environmentalfactors. For instance, changes in heterococcolithophore assemblageswere best linked to the combination of [CO2􀀀� 3 ],pH, and salinity ( D0.57), although salinity might be notfunctionally related to coccolithophore assemblage distribution.Holococcolithophores, on the other hand, showedhigher abundances and species diversity in oligotrophic areas(best fit, D0.32 for nutrients), thriving in nutrient-depletedwaters. Clustering of heterococcolithophores revealed threegroups of species sharing more than 65% similarities. Theseclusters could be assigned to the eastern and western basinsand deeper layers (below 50 m), respectively. In addition, thespecies Gephyrocapsa oceanica, G. muellerae, and Emilianiahuxleyi morphotype B/C are spatially distributed togetherand trace the influx of Atlantic waters into the MediterraneanSea. The results of the present work emphasize the importanceof considering holo- and heterococcolithophores separatelywhen analyzing changes in species assemblages anddiversity. Our findings suggest that coccolithophores are amain phytoplankton group in the entire Mediterranean Seaand can dominate over siliceous phytoplankton. They havelife stages that are expected to respond differently to the variabilityin seawater carbonate chemistry and nutrient concentrations.

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espagnol; castillan. Versión del editor