Allelopathic Effects of Alexandium spp. on Growth of Prorocentrum donghaiense Lu: Is It Toxin Dependent?

The allelopathic properties of three Alexandrium species: A tamarense (ADHK), A. minimus (AM-1) and A. catenella (ACDH), on one species of dinoflagellate Prorocentrum donghaiense were determined using bioassays of allelopathic test. Their culture filtrates were prepared at different growth phases of exponential (EP) and stationary one (SP), and were applied for the cultivation of P. donghaiense in the co-culture. Results revealed that all the culture filtrates presented growth inhibition on the co-cultured P. donghaiense, among which ADHK presented the most severe inhibition. Culture filtrates at SP showed stronger inhibition as compard to that in EP, and the dilution of the culture filtrates could alleviate their negative effects. Analysis on hemolytic activity presented that all of the Alexandrum species had hemolytic activity, which was consistent with their reported PSP toxins. It was thus speculated that the toxin-independent allelochemical(s) were involved in the noxious effects of Alexandrum spp. on P. donghaiense.