Effect of irradiance and temperature on the growth rate of Thalassiosira curviseriata Takano (Bacillariophyceae), a bloom diatom in Bahia Blanca estuary (Argentina)

Abstract

Long-term phytoplankton studies in the Bahia Blanca estuary showed a seasonal pattern characterized by a winter-early spring bloom of diatoms dominated by Thalassiosira curviseriata. Laboratory experiments were carried out to elucidate the influence of irradiance, temperature and salinity on the growth rate of T.curviseriata. The maximum daily growth rate was 1.93 divisions at 20°C. The compensation point (Ic) varied from approaching zero to 3.08 µmol m-2 s-1, a values were ~0.020-0.070 divisions µmol-1, and the calculated Ik (the irradiance at which initial slope line reaches the maximum rate of growth) varied between 32 and 36 µmol m-2 s-1. Growth became light saturated (when µ = µmax) between 70 and 80 µmol m-2 s-1, and was inhibited at ~150 µmol m-2 s-1 at all tempera- tures (5-20oC). The range of temperatures at which T.curviseriata can grow (5-20°C) coincides with the temperature range over which it is found in the field. In contrast, the thermal optimum for growth, 20°C, was higher than the range of temperatures (between 5 and 10°C) characteristic of the winter-early spring bloom in Bahia Blanca estuary. The mean specific growth rate of T.curviseriata was not affected by salinity over the tested range between 25 and 40 p.p.t. Field observations and experimental data support the characterization of T.curviseriata as a eurythermal and euryhaline species adapted to growth at relatively low light intensity. These characteristics may explain the ability of T.curviseriata to flourish seasonally when light conditions are apparently limiting and its presence almost year round under variable conditions of temperature and salinity.