MICROBIAL-DEGRADATION OF PHAEOCYSTIS MATERIAL IN THE WATER COLUMN

Observational evidence shows that the large amounts of mucilaginous substances produced by blooms of Phaeocystis colonies largely resist rapid microbial degradation in surface waters of most Phaeocystis-dominated ecosystems. In this paper the biodegradability of Phaeocystis colony-derived material is analysed with respect to current knowledge and novel data on the chemical nature of Phaeocystis material in relationship with specific bacterial enzymatic activities. Particular emphasis is given to the chemical nature of Phaeocystis colony matrix which constitutes more than 80% of total colony biomass at maximum development. This analysis gives evidence of the potential biodegradability of this mucilaginous material made of nutrient-deprived polysaccharides. Other factors controlling microbial degradation as the production of antibacterial substances by Phaeocystis colonies, cold temperature and lack of inorganic nitrogen and phosphate are further considered. It is concluded that nutrient limitation currently observed at the senescent stage of Phaeocystis blooms might well explain the low biodegradability of Phaeocystis material. However the lack of bacteria attached to colonies during the exponential phase of Phaeocystis bloom development are not clearly understood and needs further investigations.