Competition experiments under varying elemental ratios of the media, modes of nutrient supply and growth irradiance

The diatoms Skeletonema costatum and Chaetoceros debilis, the dinofla gellate Prorocentrum minimum, the cryptophycea Rhodomonas spp. and th e coccolithophorid Emiliania huxleyi were grown under different eleme nt ratios (NP25 vs. NP10), modes of nutrient supply (pulsed vs. conti nuous) and growth irradiance (low vs. high). S. costatum had the high est growth rate at low NP ratios and pulsed supply, but performed wel l at all experimental conditions. E. huxleyi prefer high NP ratios, c ontinuous supply and high light. Low NP resulted in a marked decrease in growth rate. The other diatom, C. debilis showed much of the same behavior as S. costatum, but with a lower growth rate at all conditi ons. Rhodomonas spp. competed best under high NP ratios and pulsed su pply of nutrients. The species was removed by the dilution rate unde r low NP and continuous supply. P. minimum had growth only under NP25 , continuous supply and high/low light. For the rest of the experimen ts the species was removed by the dilution rate of the chemostats. An interesting point for all of the competition experiments was a high degree of coexistence under different experimental conditions. Variat ion in dominating algal species will be discussed with regard to nutr ient- and light- limitation parameters.