Development of Anabaena blooms in a small reservoir with dense sediment akinete population, with special reference to temperature and irradiance

Author： Tsujimura Shigeo Okubo Takuya

Publisher： Oxford University Press

ISSN： 1464-3774

Source： Journal of Plankton Research, Vol.25, Iss.9, 2003-09, pp. : 1059-1067

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Abstract

The development of Anabaena ucrainica blooms in a small agricultural reservoir was monitored in 1998 and 1999. In the reservoir, numerous Anabaena akinetes were found in all regions of the sediment analyzed, with an average cell density in the uppermost layer (0–2 cm) of 1.5 × 10⁴ cm⁻³. Anabaena ucrainica filament numbers began to increase exponentially in mid-May 1998 and in late April 1999, when the water temperature exceeded 15°C. The average in situ net growth rate was 0.18 day⁻¹ as measured by filament numbers. The effect of temperature on germination of the akinetes was investigated using Anabaena akinetes taken from the reservoir sediment. High germination percentages were observed at temperatures between 14 and 23°C; however, the Anabaena akinetes did not germinate without irradiance. Growth experiments using an axenic culture of A. ucrainica isolated from the reservoir showed that an increase in incubation temperature to 26°C resulted in a rise in the specific growth rate. Consequently, it was hypothesized that temperature increases could similarly enhance the growth rate of A. ucrainica during bloom development. Furthermore, judging from the in situ growth rate of A. ucrainica, initial inocula arising from dense akinete populations in the sediment would advance bloom formation and could enhance the relative probability of Anabaena bloom formation.