Populations density-dependent competition of dinoflagellate Cochlodinium polykrikoides and Alexandrium affine

Abstract

We performed the bioassay using C. polykrikoides and A. affine cultures to evaluate their competitive relationship related with populations density-dependent values under different temperature condition. In growth experiments, dinoflagellate C. polykrikoides did not grow at 20 psu of 25 °C and 27°C, and it was dead within 2 days in all cultivation of 30°C. The maximum growth rate (μmax) of C.polykrikoides was 0.31 d-1at 25°C of 32 psu. A. affine showed negative growth rates at 15°C, but it grew well in all salinity at 20 °C to 30 °C. The maximum growth rate (μmax) of A. affine was 0.43 d-1 at 25°C of 30 psu. In co-cultivation, A. affine had a competitive advantage at all temperatures, which of 1: 1 ratio of initial cell density of both species. In co-cultivations of gradient initial cell density (1:3 1:10 and 1:100), the species had higher initial cell density showed a competitive advantage, except for 30°C. Although the initial concentration of A. affine was lower, it was dominated due to extinction of C. polykrikoides in 30°C. bioassay indicated that A. affine prevailed over C. polykrikoides in relatively lower salinity and higher temperature levels, which may have an important role in determining the succession of both HABs.e C. polykrikoides did not grow at 20 psu of 25 °C and 27°C, and it was dead within 2 days in all cultivation of 30°C. The maximum growth rate (μmax) of C.polykrikoides was 0.31 d-1at 25°C of 32 psu. A. affine showed negative growth rates at 15°C, but it grew well in all salinity at 20 °C to 30 °C. The maximum growth rate (μmax) of A. affine was 0.43 d-1 at 25°C of 30 psu. In co-cultivation, A. affine had a competitive advantage at all temperatures, which of 1: 1 ratio of initial cell density of both species. In co-cultivations of gradient initial cell density (1:3 1:10 and 1:100), the species had higher initial cell density showed a competitive advantage, except for 30°C. Although the initial concentration of A. affine was lower, it was dominated due to extinction of C. polykrikoides in 30°C. bioassay indicated that A. affine prevailed over C. polykrikoides in relatively lower salinity and higher temperature levels, which may have an important role in determining the succession of both HABs.2