ABSTRACT. – During a 15-month survey of standing stock phytoplankton at three coastal sites along Kerguelen Main Island, some hydrological as well as biological parameters differences between sites were noticed. The more sheltered site, at the head of the large Port-Raymond fjord (PRAY) on the north side of Morbihan Bay, was characterized by high and relatively stable salinity, a well defined cycle of phytoplankton biomass (up to 2 μg Chl a l^-1, November-January), and high ammonium concentrations following the phytoplankton bloom (January-February, up to 5 μM) that were probably also related to kelp degradation. At Port-Aux-Français (PAF), at the entrance of the Morbihan Bay, the salinity decreased with increasing water discharge in winter; the bloom, starting with the spring increase in water temperature, was intense and consisted of several short peaks in summer (late November-February, up to 11.2 μg Chl a l^-1 in 1992). The third site, at the head of the deep Portes-Noires fjord (PN), South Kerguelen, was characterized by frequent discharges from glacier-rivers, very low water temperature (min. 2^oC in August, max. 5^oC in January-March), low N_H⁴ + values (< 0.5 μM in winter), and a phytoplankton bloom apparently short and starting in February-March (up to 4 μg Chl a l^-1 in 1992). The ratio Chl a/Phaeo a also suggested that the phytoplankton productive period started later in the year at Portes-Noires fjord, in relation to its more exposed position. By comparison, in the offshore coastal waters (i.e. “KERFIX station”), the bloom was restricted to a short period (November-December) with low pigment maximum (up to 1 μg Chl a l^-1). The indented geomorphology of Kerguelen main Island, close to the Polar Front, allows the phytoplankton to develop actively in the inner fjords and bays, with nutrients supplied mainly from the oceanic Antarctic Divergence, but probably also from the kelp and epiphyte degradation and the flourishing macrofauna physiology. A geographical gradient in productivity was shown, from high biomasses in the Morbihan Bay, to a delayed cycle, low biomasses and nutrients, in the southern fjord with more direct open-ocean influence.