GROWTH OF HARMFUL MARINE-ALGAE IN MULTISPECIES CULTURES

Mixtures of harmful and harmless algae were grown in discontinuously d iluted batch cultures under ammonium, nitrate and phosphate limitation , and at different irradiances (20-500 mu mol quanta m(-2) s(-1)). The species used were Chrysochromulina polylepis, Emiliania huxleyi type B, Rhodomonas sp., the dinoflagellates Fibrocapsa japonica, Gymnodiniu m simplex, Gyrodinium aureolum, Heterocapsa triquetra, Heterosigma car terae, Prorocentrum micans and Alexandrium tamarense, the diatoms Chae toceros socialis, Cymatosira belgica, Ditylum brightwellii, Lauderia b orealis, Odontella aurita, Pseudonitzschia pungens, Streptotheca tames is, and the cyanobacterium Synechococcus. Their growth response in the mixed algal cultures is discussed in relation to their abundance in d ifferent natural habitats. In comparison with the other non-diatoms, t he mixotrophic C. polylepis grew fast under all tested nutrient and li ght limitations Emiliania huxleyi grew well under nitrogen (N) limitat ion (with nitrate as N source) and at irradiance levels from 15 up to 500 mu mol quanta m(-2) s(-1). No growth of calcifying cells could be detected under N limitation when ammonium was used as N source. Rhodom onas grew reasonably well under ammonium-N limitation and grew fast at the highest irradiance. The dinoflagellates were poor competitors com pared to the Prymnesiophyceae. The environmental fitness of the Prymne siophyceae appears to be closely related to the reproductive capacity of the vegetative stage, whereas the natural distribution of dinoflage llates seems more closely dependent on the generative reproduction-rel ated specific life cycle characteristics of the individual species. Th e marine diatoms include a mixture of both types of species. Some mari ne diatom species clearly have the capability to outcompete non-diatom s under different types of nutrient and light limitations when silicat e is in excess. Other diatoms seem to be poor competitors.