Competitive interaction between diatom Skeletonema costatum and dinoflagellate Prorocentrum donghaiense in laboratory culture

Abstract

Skeletonema costatum and Prorocentrum donghaiense co-exist and appear alternately as dominant species in the natural phytoplankton community in the coastal area of the East China Sea. The mechanism that determines which of the two species dominates the succession remains unknown. We conducted a series of experiments to investigate the inter-specific relationship between S. costatum and P. donghaiense. The results of the P. donghaiense and S. costatum bialgal culture experiments indicated that S. costatum dominates P. donghaiense under high-nutrient conditions, and the interaction was independent of the initial chlorophyll a ratios. Adding S. costatum culture filtrates did not significantly influence the growth of P. donghaiense and S. costatum under high-nutrient conditions. Under low-nutrient conditions, the S. costatum filtrates showed a significant autoinhibitory effect, but they did not inhibit the growth of P. donghaiense because of the tolerance of P. donghaiense to allelochemicals. The results demonstrated that the autoallelopathy of S. costatum plays an important role in the competition and succession between S. costatum and P. donghaiense under low-nutrient concentrations, especially during phosphate deficiency.