The succession mechanism of blooming species caused by Interaction between phytoplankton and bacteria in Masan Bay

Abstract

Phytoplankton blooms lead to increase in dissolved organic matter (DOM) concentration and change its composition in marine environments. Due to differences in DOM consumption depending on bacterial taxa, increase in DOM level and change in DOM composition can lead to variation in the assemblage of bacterial community (BC). The BC may affect phytoplankton growth and composition, however, the effect of BC variation on phytoplankton community is greatly unknown. In this study, we investigated changes of BC induced by the addition of DOM released from Heterosigma akashiwo (Raphidophyte), then examined effects of variation of BC on the growth of toxic dinoflagellate Prorocentrum minimum and diatom Skeletonema costatum. The BC was (Masan Bay, Republic of Korea) when blooms of H. akashiwo occurred, and incubated for three days after addition of DOM H. akashiwo culture at a final concentration of 10 mg L-1. Several bacterial genera derived from DOM represented statistical differences. Particularly, relative ratios of sphingobacteriia and verrumicobiae increase than control. Then, the treated BC was inoculated into P. minimum and S. costatum cultures two phytoplankton species. As a result, the growth of P. minimum (76 to 220 %) was clearly enhanced when DOM-treated BC was inoculated, whereas, the growth of S. costatum was suppressed (-24 to –28 %). Several bacterial genera in BC which co-cultivated with two phytoplankton species represent statistical difference compared with control, particularly, Verrumicobiae and Sphingobateriia. The ratio of these two classes and humic acid-like carbon (HL) fraction in H. akashiwo released DOM have shown high correlation coefficient. Our results showed that the species-specific composition of DOM can change bacterial community composition that promotes the growth of different phytoplankton taxa.