SEASONAL IMPACT OF THE MICROZOOPLANKTON ON PICOPLANKTON AND NANOPLANKTON GROWTH-RATES IN THE NORTHWEST MEDITERRANEAN-SEA

The effect of protozoan presence on pico- and nanoplankton growth rates was studied during a whole seasonal cycle, together with several other environmental factors (such as microphytoplankton abundance, temperature, salinity, solar irradiance and nutrients). Pico- and nanoplankton growth rates were enhanced in the presence of protozoa inside a dialysis bag and reached values as high as 0.08 to 0.2 h-1. At in situ concentrations (10(6) flagellates l-1 and 10(3) ciliates l-1), protozoa, through their excretory activity, played an important role in phytoplankton growth. However, other environmental factors, such as allochthonous nutrients and temperature, also have an effect on these growth rates.