Growth and competition for different forms of organic phosphorus by the dinoflagellate Prorocentrum donghaiense with the dinoflagellate Alexandrium catenella and the diatom Skeletonema costatum s.l.

Abstract

Growth and competition between the dinoflagellates Prorocentrum donghaiense and Alexandrium catenella and the diatom Skeletonema costatum sensu lato in response to different forms of phosphorus were investigated in mixed cultures. The results indicated that S. costatum s.l. outcompeted P. donghaiense to become dominant owing to high growth rates, irrespective of the KH2PO4 content or any dissolved organic phosphorus (DOP) substrate. However, P. donghaiense densities in the DOP substrates, particularly lecithin, grew to 2–4 times higher than those in KH2PO4. The growth rates of P. donghaiense and A. catenella were comparable. A. catenella densities decreased when the phosphorus substrate was changed from inorganic to organic, and P. donghaiense outcompeted A. catenella only when lecithin was added. Abundant alkaline phosphatase (AP) was expressed when the external phosphate was lower than 0.1 μmol l−1. The highest bulk AP activities in the lecithin treatments suggested that lecithin might be more difficult to hydrolyze by these algae compared with glucose-6-phosphate and ribonucleic acid. We suggested that the advantage which P. donghaiense was shown to have in utilizing DOP for growth is what allowed it to become abundant or even dominant in natural communities when phosphate was depleted.