Differential interactions between the bloom-forming dinoflagellates Karenia bicuneiformis and Karenia selliformis and heterotrophic dinoflagellates

Abstract

Many species of the dinoflagellate genus Karenia produce neurotoxins and often cause harmful algal blooms. Heterotrophic dinoflagellates are major grazers of bloom-forming dinoflagellates. Therefore, to understand the population dynamics of Karenia species, it is necessary to investigate the interactions between Karenia species and their potential heterotrophic dinoflagellate predators. We examined the interactions between the bloom-forming dinoflagellates Karenia bicuneiformis and Karenia selliformis and eight common heterotrophic dinoflagellates. Gyrodinium dominans, Gyrodinium moestrupii, Oxyrrhis marina, Oblea rotunda, and Protoperidinium pellucidum fed on K. bicuneiformis, whereas Gyrodiniellum shiwhaense, Pfiesteria piscicida, and Noctiluca scintillans did not. Furthermore, K. bicuneiformis supported the positive growth of G. dominans, G. moestrupii, O. marina, and P. pellucidum, but K. bicuneiformis did not support the growth of O. rotunda. With increasing prey concentration, the growth and ingestion rates of P. pellucidum on K. bicuneiformis increased and then became saturated. Maximum growth and ingestion rates of P. pellucidum on K. bicuneiformis were 0.19 d-1 and 0.86 ng C predator-1 d-1 (1.26 cells predator-1 d-1), respectively. However, all eight heterotrophic dinoflagellates tested were lysed by K. selliformis. At a K. selliformis concentration of 100 cells mL-1 within 48 h, the survival of G. dominans and G. moestrupii was only 0 and 13%, respectively. Therefore, K. bicuneiformis can be prey for the heterotrophic dinoflagellates, whereas K. selliformis kills them. These differential interactions may have resulted in different ecological niches for these two Karenia species. © 2024 The Korean Society of Phycology.