WANG Yan, SHEN Ping-ping, and QI Yu-zao, Institute of Hydrobiology, Jinan University, Guangzhou 510632, China)

Abstract

Two different strains of Phaeocystis globosa were isolated respectively from the South China Sea coastal waters of Hong Kong (HK) and Shantou (ST) in Guangdong Province. The morphology, life cycle and growth curves of the two strains under laboratory conditions were examined in the present study. The life cycle of P. globosa is complex and heteromorphic, exhibiting alternations between two different morphological forms - free-living cells (motile and non-motile cells) and colonies. The free-living cells of the two strains were showed in globular form about 3-9 µm in diameter while the colonies were different in size. The maximum diameter of ST colony collected from seawater was 3.0cm, which was much larger than that of HK colony. The free-living cells reproduced by repeated bipartition and these cells were aggregated forming a colony. Continuous cell division and subsequent enlargement resulted in the growth of colony. When the nutrition in the medium were depleted, the colonies were lysised or decayed and thousands of free-living cells were released. The entire growth cycle of P. globosa took 20-30 days in batch culture. The growth rate of two strains varied from each other under three different temperatures(20, 25 and 30°C), and the optimal growth temperature was 25°C for the HK strain and 30°C for ST strain. The maximum specific growth rate were 0.38 and 0.42 for HK and ST strains, respectively. Temperature becomes one of the important limiting factors, which affect the growth of the two strains.

Key words: Phaeocystis globosa, Life cycle, Morphology, Growth curve