The most important features enhancing primary production and phytoplankton biomass are coastal upwelling, coastal run‑off and river plumes, seasonal currents, and internal waves and tidal fronts. Concentrations of toxic dinoflagellates exhibit interannual variations that are determined mainly by changes in the upwelling regime, river run-off, inoculum size, and other environmental parameters.
The abundance of autotrophic picoplankton in the mid-shelf of the central part of the north Iberian coast does not show a significant long-term trend, but heterotrophic picoplankton show a significant long-term increase that has been associated with warming of the sea surface in this area.