Density-dependent inhibition among four major dinoflagellate species causing red tides in Korean waters

Abstract

In red-tide dynamics, one species often predominates microalgal communities after severe competition among several species. In Korean waters, Prorocentrum donghaiense, Tripos fusus, Alexandrium fraterculus, and Margalefidinium polykrikoides form red tides, which sometimes cause massive fish kills and economic losses. When two of these species were cultivated together, M. polykrikoides inhibited the growth of A. fraterculus, P. donghaiense, and T. fusus at a M. polykrikoides abundance of 610, 2230, and 410 cells mL-1, respectively. Alexandrium fraterculus inhibited the growth of P. donghaiense and T. fusus at a A. fraterculus abundance of 840 and 10 cells mL-1, respectively. Prorocentrum donghaiense inhibited the growth of T. fusus at a P. donghaiense abundance of 2020 cells mL-1. Our field data on the abundance of these species in 2014 show that the abundances of A. fraterculus, P. donghaiense, and T. fusus were less than 10 cells mL-1 when that of M. polykrikoides exceeded 500 cells mL-1. Therefore, the red-tide formation of one of these four species can be affected by the high abundance of the others, which is an example of density-dependent inhibition.