Winter presence of prochlorophytes in surface waters of the northwestern Mediterranean Sea

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Abstract
Cells with characteristics similar to the recently discovered oceanic prochlorophytes have been detected with ship‐board flow cytometry during winter in the surface waters of the northwestern Mediterranean Sea as well as in the low‐salinity dilution zone of the Rhône River. Maximum abundances reached 50,000 cells ml−1 at the surface and were only slightly lower than those observed previously at the bottom of the euphotic zone in the Atlantic and Pacific Oceans. The concentration, light scatter, and pigment fluorescence of these cells correlated tightly with those of Synechococcus spp. cyanobacteria. These results point out that the ecological niches of oceanic prochlorophytes are probably more diverse than initially thought.