Jin Hee Ok’s research while affiliated with Hanyang University and other places

Species and genera in the dinoflagellate family Kareniaceae have attracted the attention of scientists, aquaculture farmers, and government officials because many species in this family cause harmful algal blooms associated with the mortality of vertebrates and invertebrates. In addition, the genera in Kareniaceae exhibit different morphological, biochemical, and genetic characteristics. To understand bloom dynamics and eco-evolutionary strategies of the genera in Kareniaceae, the biological interactions of kareniacean species and genera with prey and predators should be explored. In the present study, we reviewed the trophic modes, prey taxa and size spectra, feeding mechanisms, growth and ingestion rates, and protistan predators of five genera Gertia, Karenia, Karlodinium, Shimiella, and Takayama in the family. Additionally, we explored the feeding occurrence in Gertia stigmatica, the prey spectrum of Karenia brevis, and the predation of Takayama tasmanica by heterotrophic protists, which have not been fully investigated prior to the present study. Karenia, Karlodinium, Shimiella, and Takayama have different prey taxa and size spectra. Furthermore, within the same genus, different species exhibit different biological interactions with prey and protistan predators, creating different ecological niches. This study provides insights into the eco-evolutionary strategies of kareniacean dinoflagellates.

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.

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO2 and O2. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydaeproduction gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000–8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0–4.0 L min-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

Many dinoflagellate species are bioluminescent, which is one of the anti-predation mechanisms in these species. In addition, dinoflagellate species experience a wide range of salinities in the ocean. However, the effects of salinity on their bioluminescence intensity has only been investigated for one species. Here, we explored the effect of salinity on the bioluminescence intensity of the heterotrophic dinoflagellate Noctiluca scintillans NSDJ2010 feeding on the chlorophyte Dunaliella salina, the heterotrophic dinoflagellate Polykrikos kofoidii PKJH1607 feeding on the dinoflagellate Alexadrium minutum, and the autotrophic dinoflagellate Alexandrium mediterraneum AMYS1807. Moreover, to determine the cell volume and growth effects on bioluminescence intensity, the cell volume and growth rate of three bioluminescent dinoflagellates were simultaneously investigated. The mean 200-s-integrated bioluminescence intensity (BL) per cell, equivalent to the total bioluminescence, of N. scintillans, P. kofoidii, and A. mediterraneum was significantly affected by salinity and increased with increasing salinity from 10 to 40. The results of the present study suggest that the total bioluminescence of N. scintillans, P. kofoidii, and A. mediterraneum in offshore and oceanic waters is greater than that in estuarine waters.

Copepods are a major component of metazooplankton and important prey for fish and invertebrates such as crabs, shrimps, and flatworms. Certain bloom-forming dinoflagellates can kill copepods, but there is little research on the interactions between copepods and the bloom-forming dinoflagellates Karenia bicuneiformis and K. selliformis. In this study, the survival and ingestion rates of the calanoid copepod Acartia hongi feeding on K. bicuneiformis and K. selliformis were determined as a function of prey concentration. On day 2, the survival of A. hongi incubated with K. bicuneiformis was 90–100% at all the tested prey concentrations, while that with K. selliformis was 0–20% at ≥ 582 ng C mL⁻¹. Compared to other harmful dinoflagellates from the literature, K. bicuneiformis caused low mortality of Acartia; however, K. selliformis caused almost the highest mortality at similar dinoflagellate concentrations. With increasing mean prey concentration, the ingestion rates of A. hongi feeding on K. bicuneiformis increased on day 1, but those on K. selliformis did not increase. Acartia hongi stopped feeding on K. bicuneiformis at mean prey concentrations of ≥ 341 ng C mL⁻¹ and K. selliformis at all prey concentrations on day 2. At the prey concentration of 1000 ng C mL⁻¹, the ingestion rate of A. hongi feeding on K. bicuneiformis was moderate among the rates of Acartia spp. feeding on harmful dinoflagellates; however, that on K. selliformis was the lowest. These results indicate that K. bicuneiformis and K. selliformis differentially affect the survival and ingestion rates of A. hongi.

Many dinoflagellates produce bioluminescence. To estimate the intensity of bioluminescence produced by populations of the heterotrophic dinoflagellates Noctiluca scintillans and Polykrikos kofoidii and autotrophic dinoflagellate Alexandrium mediterraneum in Korean waters, we measured cellular bioluminescence intensity as a function of water temperature and calculated population bioluminescence intensity with cell abundances and water temperature. The mean 200-second-integrated bioluminescence intensity per cell (BL_cell) of N. scintillans satiated with the chlorophyte Dunaliella salina decreased continuously with increasing water temperature from 5 to 25°C. However, the BL_cell of P. kofoidii satiated with the mixotrophic dinoflagellate Alexandrium minutum continuously increased from 5 to 15°C but decreased at temperatures exceeding this (to 30°C). Similarly, the BL_cell of A. mediterraneum continuously increased from 10 to 20°C but decreased between 20 and 30°C. The difference between highest and lowest BL_cell of N. scintillans , P. kofoidii , and A. mediterraneum at the tested water temperatures was 3.5, 11.8, and 21.0 times, respectively, indicating that water temperature clearly affected BL_cell. The highest estimated population bioluminescence intensity (BL_popul) of N. scintillans in Korean waters in 1998–2022 was 4.22 × 10¹³ relative light unit per liter (RLU L^-1), which was 1,850 and 554,000 times greater than that of P. kofoidii and A. mediterraneum , respectively. This indicates that N. scintillans populations produced much brighter bioluminescence in Korean waters than the populations of P. kofoidii or A. mediterraneum .

Global warming is exacerbating coastal hypoxia by intensifying stratification. Marine hypoxia often causes large-scale mortality of fish, shellfish, and mammals. However, there have only been a few studies on the effect of hypoxia on dinoflagellate survival. Here, we explored the hypoxic effects on the growth rates of dinoflagellates with different trophic modes: autotrophic Alexandrium fraterculus and Scrippsiella lachrymosa; mixotrophic Alexandrium pohangense, Gymnodinium smaydae, and Shimiella gracilenta; and heterotrophic Gyrodinium dominans and Protoperidinium pellucidum. Additionally, we tested feeding as a tactic to reduce hypoxia-induced mortality. Hypoxia reduced the growth rates of all the tested species. However, feeding suitable prey to A. pohangense, G. smaydae, S. gracilenta, G. dominans, and P. pellucidum reduced their mortality due to hypoxia. Furthermore, feeding enabled A. pohangense and G. dominans to survive under hypoxic conditions. Therefore, feeding could be used as a strategy for survival and reduction of mortality in mixotrophic and heterotrophic dinoflagellates against hypoxia.