Fine-scale structuring of surface picophytoplankton communities in the ultra-oligotrophic Southeastern Mediterranean Sea

Abstract The spatial distribution of phytoplankton is characterized by distinct fine-scale (1-100km) patchiness associated with mesoscale and sub-mesoscale ocean dynamics. While fine-scale patchiness in total phytoplankton biomass is often observed in satellite and in-situ data, fine-scale structuring of phytoplankton communities is still rarely documented, limiting our ability to accurately characterize ocean biodiversity. Here we show results from a high resolution study aimed at characterizing fine-scale variations in the community composition of picophytoplankton inhabiting the summertime surface waters of the Southeastern Mediterranean. Combining high resolution (30m) Landsat imagery and in-situ measurements along two transacts, we show that in the ultra-oligotrophic conditions characterizing this region picophytoplankton may be assembled in fine-scale patches that significantly differ in their community composition. The separated patches are also characterized by distinct signatures in the surface temperature and salinity space, providing observational evidence to the phytoplanktonic landscape being organized in segregated fine-scale assemblages that differ in their life history. Our results indicate that fine-scale variability patterns and the processes underlying their formation should be considered when investigating ecological and biogeochemical processes in oligotrophic waters, and demonstrate the potential of harnessing very high resolution satellite data (~10 m) for that purpose.