• ALGAE
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• v.38 no.1
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• pp.39-55
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• 2023

Exploring mixotrophy of dinoflagellate species is critical to understanding red-tide dynamics and dinoflagellate evolution. Some species in the dinoflagellate genus Karenia have caused harmful algal blooms. Among 10 Karenia species, the mixotrophic ability of only two species, Karenia mikimotoi and Karenia brevis, has been investigated. These species have been revealed to be mixotrophic; however, the mixotrophy of the other species should be explored. Moreover, although K. mikimotoi was previously known to be mixotrophic, only a few potential prey species have been tested. We explored the mixotrophic ability of Karenia bicuneiformis, Karenia papilionacea, and Karenia selliformis and the prey spectrum of K. mikimotoi by incubating them with 16 potential prey species, including a cyanobacterium, diatom, prymnesiophyte, prasinophyte, raphidophyte, cryptophytes, and dinoflagellates. Cells of K. bicuneiformis, K. papilionacea, and K. selliformis did not feed on any tested potential prey species, indicating a lack of mixotrophy. The present study newly discovered that K. mikimotoi was able to feed on the common cryptophyte Teleaulax amphioxeia. The phylogenetic tree based on the large subunit ribosomal DNA showed that the mixotrophic species K. mikimotoi and K. brevis belonged to the same clade, but K. bicuneiformis, K. papilionacea, and K. selliformis were divided into different clades. Therefore, the presence or lack of a mixotrophic ability in this genus may be partially related to genetic characterizations. The results of this study suggest that Karenia species are not all mixotrophic, varying from the results of previous studies.

• Journal of Marine Life Science
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• v.8 no.2
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• pp.190-195
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• 2023

In this research, the marine medaka Oryzias javanicus underwent a 96 h exposure to two concentrations of the red tide dinoflagellate Karenia mikimotoi (1,000 and 5,000 cells mL^-1), and the temporal variations in biochemical responses related to antioxidant and immunity parameters were assessed in the liver tissue. The study revealed a significant increase in ichthyotoxicity with elevated cell concentrations of K. mikimotoi, especially evident at 96 h in marine medaka exposed to 5,000 cells mL^-1. At 1,000 cells mL^-1 of K. mikimotoi, the opercular respiratory rate showed a significant increase, whereas exposure to 5,000 cells mL^-1 resulted in a lowered rate. The intracellular malondialdehyde content was significantly elevated in response to both cell concentrations at 96 h. Regarding glutathione content, levels were significantly increased by exposure to both cell concentrations. Catalase and superoxide dismutase enzymatic activities experienced an increase at 1,000 cells mL^-1 of K. mikimotoi, while their activities were reduced at 5,000 cells mL^-1 at 96 h. The analysis of two immunity parameters, alternative complement pathway and lysozyme, demonstrated significantly reduced activities in the liver tissue exposed to 5,000 cells mL^-1 of K. mikimotoi. These findings aim to enhance the understanding of K. mikimotoi toxicity in marine fish by offering insights into biochemical responses associated with harmful algal blooms.

• Proceedings of KOSOMES biannual meeting
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• 2009.06a
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• pp.155-155
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• 2009

• Proceedings of the Korean Aquaculture Society Conference
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• 2004.05a
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• pp.178-179
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• 2004

• Korean Journal of Environmental Biology
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• v.28 no.3
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• pp.115-124
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• 2010

In order to find out the short-term phytoplankton dynamics during summer season in Jinhae Bay, we investigated the environmental factors and phytoplankton population densities at 16 stations. A total of 66 phytoplankton species were appeared, diatoms occupied more than 80% of total species, and the others were dinoflagellates and raphidophyceaes. The dominant species were diatoms Chaetoceros affinis, C. didymus, C. pseudocurvisetus, Leptocylindrus danicus, Pseudonitzchia pungens, Skeletonema costatum and dinoflagellates Cochlodinium polykrikoides, Gymnodinium impudicum, Karenia mikimotoi, Prorocentrium minimum, Protoperidinium bipes and Scrippsiella trochoidea. According to multidimensional scaling (MSD) and cluster analysis based on phytoplankton community data from each station, the Jinhae bay was divided into two groups. The first group included stations in the inner part of Masan Bay, which is strongly influenced by high nitrogen loading and low salinity by river discharge. The second group included the other remained stations. Based on canonical correspondence analysis (CCA), small-size dinoflagellates K. mikimotoi, P. minimum, P. bipes and S. trochoidea and centric diatom C. pseudocurvisetus and S. costatum, which is dominanted in the inner area of bay, were related with DIN (ammonium, nitrate, nitrite). These results imply that the study area was grouped into the two water masses (inner and outer water of Masan Bay) and inner waters had higher phytoplankton abundances and Chl.a concentration than outer waters. As a result, summer phytoplankton peaks in the inner shallow bay were stimulated by increases in nitrogen and temperature.

• ALGAE
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• v.23 no.1
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• pp.15-29
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• 2008

Many species in Gymnodiniales, which are unarmored dinoflagellates, are responsible for marine algal blooms and some of them have potent toxin in the cell. Their taxonomy has so far been well-defined, and several genera (e.g. Akashiwo, Gymnodinium, Karenia) have recently been re-described. In Korea, few works have been carried out on their taxonomical and molecular studies. This study focused on comparison of both morphological and molecular characteristics of five unarmored dinoflagellates on Korean coastal water: Akashiwo sanguinea, Cochlodinium polykrikoides, Gymnodinium catenatum, Gymnodinium impudicum and Karenia aureolum (=K. mikimotoi). Morphological characteristics observed here was in good accordance with the original descriptions of individual species. In addition, none of difference was found in morphological comparisons between the Korean and foreign strains. Furthermore, molecular analysis showed that the SSU rDNA sequences were generally identical according to each species. In some distinct features, A. sanguinea, which has generally the same morphological features, were divided into two groups: one was Korean isolates including European isolates, the other was American isolates. In the two groups, the nucleus was positioned differently: middle of the cells in the Korean isolates (GnSg02, GnSg03), near the epicone in American isolates (CCMP1593, CCMP1837). In addition, this was strongly supported by phylogenetic analysis, inferred from the SSU rDNA sequences. K. aureolum (GrAr01) was corresponded to European G. aureolum (=K. mikimotoi) in shape and position of nucleus, chloroplast, however, which is similar to K. digitata in view of having a finger-like sulcus. This was in good agreement with phylogenetic study of these species. G. catenatum have identical morphology except the ridge location, and their genotype of SSU rDNA was also identical to GenBank data of the same species. From this study, we found that the five Korean unarmored dinoflagellates are identical morphological characteristics and genotype to each species of foreign isolates.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.523-530
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• 2020

Based on the results of harmful algal blooms (HABs) monitoring by the National Institute of Fisheries Science and local governments, the effects of changes in the marine environment on HABs are described. Since the beginning of HABs monitoring in 1972, they continued to increase from the 1980s to the 1990s. After the largest number of HAB incidents (109) in 1998; the trend declined until the 2010s. Most HABs in the 1970s were caused by diatoms. In the 1980s, coastal dinoflagellates caused HABs; Cochlodinium polykrikoides blooms have been occurring continuously since 1993. There are three HAB species that cause damage to fisheries in Korea. The high-density bloom of Karenia mikimotoi caused mass mortality in shellfish in Jinhae Bay in 1981. Karenia sp. blooms occurring around Tongyeong in 1992 killed aquaculture fish. Since the occurrence of the largest fisheries damage of KRW 76.6 billion in 1995 caused by C. polykrikoides blooms, they have been occurring continuously. The concentration of nutrients in coastal waters was the highest in the 1980s and has declined since the mid-1990s. This reduction in nutrient concentration is a good explanation for the decreasing number of HABs. Since 2016, a summer high water temperature of 30℃ or more has appeared, and the range and scale of C. polykrikoides blooms have been greatly reduced. In 2016, K. mikimotoi blooms occurred around Wando, Jangheung and Goheung and small scale blooms of C. polykrikoides occurred around Yeosu. There were no C. polykrikoides blooms in 2017; however, Alexandrium affine blooms occurred from Yeosu to Tongyeong. There was a small-scale blooms of C. polykrikoides in 2018 compared to those in the previous years. Our results show that reduction in nutrients and the high water temperature owing to climate change are a good explanation for variation in HABs in Korean coastal waters.