Competition Trade-offs of Two Bloom Algae under Experimental Non-Steady State Nutrient Limitation

Two bloom algae of Microcystis aeruginosa Kutz(Microcystis) and Scenedesmus obliquus (Turp.) Kutz(Scenedesmus) were cultured under experimental non-steady-state conditions, using the "pulse" adding method. The result obtained of tests showed that Microcystis was almost always the predominant algae as pulse was 1d with regardless of availability of nutrients, Microcystis showed susceptible Nitrogen under Nitrogen(N) and Phosphorus(P) limits. The N:P supply ratio have a strong effect on species compositions. The symbiosis of two species was only observed under two different supply pulse(1d and 8d) under NP limits. Cells size of Scenedesmus increased as nutrient concentration decreased, becoming larger when NP nutrients limited. However, Microcystis cells size was not changed so significantly as Scenedesmus, and difference of which was no more than 3 μm² with whatever nutrient availability. Analysis of the results indicated that competition between the two algae was related to pulses under different nutrient limits. According to theory of gleaner-opportunist trade-off, Microcystis showed the characteristics of an "opportunist" and Scenedesmus was more likely to be a "gleaner". The symbiosis of two bloom species coincided with the Intermediate Disturbance Hypothesis (IDH). The two algae might change their cell size and shape to strive for more nutrients.