Influence of nutrient concentrations on the seasonal abundance and distribution of Cyanophyceae in the coastal region of Mount Cameroon

摘要

Water management in the coastal region of Mount Cameroon is threatened by extensive and persistent noxious blooms of Cyanophyceae (blue-green algae) in the surface and near-surface mesotrophic and eutrophic zones. Nutrient concentrations and species composition of Cyanophyceae were investigated from surface waters at 15 stations from three sites along the Mount Cameroon region (Mudeka Creek, Tito Creek and Idenau Beach) during the rainy season, from July to August 1999, and during the dry season, from February to March 2000. Nitrate concentrations were extremely high during the rainy season, ranging from 240.07 mg l-1 to 927.07 mg l-1, and comparatively low, ranging from 1.79 mg l-1 to 10.39 mg l-1, during the dry season. The Cyanophyceae community consisted of six genera: Microcystis, Lyngbya, Gloeocapsa, Trichodesmium, Chamaesiphon and Aphanocapsa. Three species (T. dispersa, T. lacustre and L. birgei) were present during the rainy season whereas five species, with two dominant (M. aeruginosa, G. dispersa), were present during the dry season. There was a positive correlation (r=0.73) between nutrient concentration and Cyanophyceae concentration. Water transparency depth (Secchi disc depth) was much shallower during the rainy season than during the dry season, most likely as a result of the increased leaching of insoluble material from the land and decay of Cyanophyceae blooms during the rainy season. Management strategies to limit the formation of algal blooms in the region are discussed..