Effects of temperature, salinity, and light intensity on the growth of the diatom Rhizosolenia setigera in Japan

Abstract

ABSTRACT Some species of Rhizosolenia form intense blooms, known as red tides, in Japanese coastal waters. In Tokyo Bay, Rhizosolenia setigera frequently causes red tides and sometimes causes discolouration of Pyropia in nori farms. However, little is known about the growth characteristics of R. setigera in Tokyo Bay. We evaluated the effects of temperature, salinity, and irradiance on the growth of R. setigera isolated from Tokyo Bay. Our strain grew well in SWM-3 medium and f/2 + N, P, Si, Tris medium, at 5–30 °C and salinity (S) of 20–40. Maximal growth rate was obtained at 25 °C and S of 30–35. The strain maintained a moderate growth rate (0.4 < µ < 0.6) at low temperature (c. 10–13 °C) and S of 30. The strain grew at a wide range of irradiances from 11 to 1625 μmol photons m−2 s−1, with optimum irradiance (L max) ≥ 1625 μmol photons m−2 s−1. In Tokyo Bay from 2010 to 2014, R. setigera was observed at 17.1 to 26.4 °C with S ranging from 24.6 to 31.2, and cell densities exceeding 500 cells ml−1. This corresponded to results from our culture experiments. We anticipate that the data obtained in this study may be useful for understanding the bloom dynamics of R. setigera and the underlying environmental conditions associated with nori discolouration.