Effect of allelopathy on the competition and succession of Skeletonema costatum and Prorocentrum donghaiense

Abstract

Prorocentrum donghaiense and Skeletonema costatum are typical coexisting species found in the East China Sea. However, P. donghaiense blooms usually occur after S. costatum in the spring and summer season. The mechanisms of controlling this succession remain unclear; we propose that it might be allelopathy. Bi-algal cultures in seawater and S. costatum filtrate were used to examine the effect of allelopathy on the competition between S. costatum and P. donghaiense. The result of comparable experiments between axenic and non-axenic media indicated that the active bacteria were not the predominant factor affecting the competitive results, and non-autoclaved filtrates were then used in the bi-algal culture experiments. The results of bi-algal cultures showed that S. costatum was the dominant species in the seawater when nutrient concentrations and algae ratios in the cultures were similar to those in the field. In contrast, the evident succession between S. costatum and P. donghaiense in the S. costatum cell-free filtrate culture indicated that the allelochemicals accounted for the formation of alternating dominant algae. We propose that the possible mechanism was that the extracellular chemical compounds released by S. costatum inhibited its own growth, and the growth of P. donghaiense benefited from the suppression of S. costatum growth. We conclude that allelopathy has important effects on the competition and succession of S. costatum and P. donghaiense.