Interplay between freshwater discharge and oceanic waters modulates phytoplankton size-structure in fjords and channel systems of the Chilean Patagonia

•Physical/chemical controlling factors were investigated for the entire Patagonian fjords.•Phytoplankton size classes vary with freshwater discharges and oceanic nutrient.•Fresh water discharges reduce chlorophyll-a and microphytoplankton fraction.•Oceanic nutrients favor chlorophyll-a in the southern half of the Patagonian region.