Mixed populations of marine microalgae in continuous culture: Factors affecting species dominance and biomass productivity

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Abstract
Marine microalgae were grown in multispecies continuous cultures. Under carbon dioxide limitation, blue–green algae dominated. Under nitrate and light limitation, species dominance depended on the initial conditions. When the inoculum consisted primarily of blue–green algae with smaller amounts of other species, blue–green algae and pennate diatoms dominated. When the inoculum consisted of equal amounts of all species, green flagellates and pennate diatoms dominated. Green flagellates and blue–green algae were incompatible and never shared dominance. When nutrient limitations were overcome, the productivity of seawater was increased 100-fold before light limitation occurred. The productivity could be further increased by reducing photorespiration in the culture. The dilution rates studied (0.1, 0.2, and 0.4 day−1) had no effect on species dominance, nor did the higher dilution rates select for smaller cells. The maximum productivity occurred at a dilution rate of 0.2 day−1. Temperature had the greatest effect on species dominance, with green flagellates, pennate diatoms, and blue–green algae dominating at 20°C and only blue–green algae dominating at 35°C. The productivity at 35°C was lower than that at 20°C because of the lower solubility of carbon dioxide at higher temperatures. At 10% salinity, green flagellates and pennate diatoms dominated. The productivity at this salinity was 50% that obtained at the salinity of seawater (3.5%). At 25% salinity, only the green flagellate, Dunaliella salina, survived at a productivity of 1% that obtained at the salinity of seawater.