Effects of Salinity on Growth and In Vitro Ichthyotoxicity of Three Strains of Karenia mikimotoi

Abstract

Karenia mikimotoi is one of the most damaging ichthyotoxic dinoflagellate species commonly found in China. However, its growth and ichthyotoxicity responses to salinity changes are still largely unknown. In this study, the growth and ichthyotoxicity of three K. mikimotoi strains, Hong Kong strain KMHK, Japanese strain NIES2411 and New Zealand strain CAWD133, under different salinities (25 to 35 ppt), initial algal densities (5 to 40 thousand cells) and growth phases were investigated. Results indicated that the optimum salinity for all three strains was 30 ppt. The Japanese strain achieved the highest maximum cell densities (cells mL−1) and the New Zealand strain achieved the highest specific growth rate. The Hong Kong and New Zealand strains could not tolerate the low salinity at 25 ppt and the algal cells burst after 3 days of exposure. The average cell widths of all three algal strains in 35 ppt salinity were significantly larger than that in 30 ppt. The acute toxicity test performed on Oncorhynchus mykiss gill cell line RTgill-W1 revealed that the median lethal times for KMHK and NIES2411 were 66.9 and 31.3 min, respectively, and their ichthyotoxicity was significantly affected by algal cell density and growth phase. Nevertheless, CAWD133 did not pose any ichthyotoxicity. The gill cell viability levels at 30 min were reduced from 96 to 61% and 95 to 39% for KMHK and NIES2411, respectively, when the algal cell density increased from 5 × 103 to 4 × 104 algal cells mL−1. Both KMHK and NIES2411 at stationary phase also had higher toxicity than at log phase, with a 27% reduction of gill cell viability, and exerted higher toxicity to the gill cells under extremely low (28 ppt) or high (35 ppt) salinity. These findings demonstrated that the growth–ichthyotoxicity response of Karenia mikimotoi to salinity was not only strain-specific but also depended on its density and growth phase. Study on the effects of salinity on the growth and toxicity of K. mikimotoi is greatly limited. Results from the present study provide valuable insight on the growth and toxicity of different K. mikimotoi strains, which is important in understanding their occurrence of algal bloom and fish-killing action.

Salinity decline promotes growth and harmful blooms of a toxic alga by diverting carbon flow

“…Apart from affecting growth rate, decreases in salinity might also influence the toxicity of HAB cells. Multiple strains of K. mikimotoi have been reported to cause ichthyotoxicity induced by lower salinities (Lam, Cheung, et al., 2022). Similarly, salinity declines promote toxin production of the dinoflagellates Alexandrium ostenfeldii (Martens et al., 2016), A. pacificum (Bui et al., 2021) and Lingulodinium polyedra (Peter et al., 2018) as well as the diatom Pseudo‐nitzschia australis (Ayache et al., 2020).…”

Revealing the algicidal characteristics of Maribacter dokdonensis: An investigation into bacterial strain P4 isolated from Karenia mikimotoi bloom water

“…The algal KMHK cells, cultivated in L1‐Si medium, were harvested on days 8 and 21, representing log and stationary phases, respectively, according to our previous results (Lam et al., 2022). Four different exposure combinations were prepared to investigate the effect of growth phases: (A) KS + PS: KMHK at stationary phase exposed to P4 harvested at stationary phase, (B) KL + PS: KMHK at log phase exposed to P4 at stationary phase, (C) KL + PL: KMHK at log phase exposed to P4 at log phase, and (D) KS + PL: KMHK at stationary phase exposed to P4 at log phase.…”