GROWTH CHARACTERISTICS AND LIFE CYCLE OF PHAEOCYSTIS GLOBOSA SCHERFFEL

Two different strains of Phaeocystis globosa were isolated respectively from the coastal waters of Hong Kong (HK) and Shantou (ST) of Guangdong Province. Their morphology, life cycle and growth curves under laboratory conditions with batch culture method were examined. 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 globose form about 3-9 μm in diameter while the colonies were different in size. The colonies of Shantou strain which were up to maximum 3.0 cm in diameter in field study were much larger than those of Hong Kong strain. The free-living cells reproduced by repeated bipartition and these cells were aggregated forming a colony. In these colonies, cell division and subsequent enlargement resulted in growth. When the nutrition in culture were depleted, the colonies were lysised or decayed and thousands of free-living cells were released. The growth cycle of P. globosa takes about 20-30 days in batch culture. The growth rate of two strains varied from each other under three different temperatures (20℃,25℃,30℃),and their optimal growth temperature was 25℃ for the Hong Kong strain and 30℃ the Shantou strain. Their corresponding maximum specific growth rate were 0.38 and 0.42, respectively. It is concluded that temperature was one of the important factors limiting the growth of the algae.