Seok-Hyun Youn

Distribution pattern of zooplankton in the han river estuary with respect to tidal cycle

The monthly distribution of zooplankton communities in Han River estuary was investigated at two stations from July 1998 to June 1999. Monthly mean abundance of total zooplankton varied remarkably, with the range from 20 indiv.·m-3 to 19,600 indiv.·m-3. During the study period, dominant species of zooplankton community were dinoflagellateNoctiluca scintillans, copepodsParacalanus indicus, Paracaanus crassirostris, Acartia hongi, Acartia ohtsukai, and meroplanton cirriped larvae. According to tidal states, relative high abundance occurred at high tide without regard to season. The temporal distribution of abundance implied that the reduced salinity probably limited the zooplankton populations and the fluctuations of salinity were an important factor in the variation of abundance. However, the results of salinity tolerance test shows that the variations in salinity do not directly influence the decrease of abundance. This study shows that the relatively high abundance of zooplankton near high tide seems to be related with the expansion of abundant zooplankton inhabiting Incheon coastal waters through tidal currents.

Grimontia marina sp. nov., a marine bacterium isolated from the Yellow Sea

A novel species belonging to the genus Grimontia is described in this study. A Gram-negative, chemoheterotrophic, obligately aerobic, catalase- and oxidase-positive, motile by a single polar flagellum, and rod-shaped bacterium, designated IMCC5001T, was isolated from surface seawater of the Yellow Sea. Strain IMCC5001T grew optimally at 30°C in the presence of 3.5% NaCl. Phylogenetic analysis based on 16S rRNA gene sequences showed that the isolate was related most closely to Grimontia hollisae with a sequence similarity of 95.8%, and formed a robust phyletic lineage with Grimontia hollisae. Differential physiological characteristics between the new strain and Grimontia hollisae KCCM 41680T and chemotaxonomic characterization including determination of DNA G+C content, fatty acid methyl esters, quinone composition, and polar lipid profiles justified the assignment of strain IMCC5001T to the genus Grimontia as a novel species. In conclusion, strain IMCC5001T represents a new species, for which the name Grimontia marina sp. nov. is proposed, with the type strain IMCC5001T (=KCTC 22666T =NBRC 105794T).

Enhanced photobiological H2 production by the addition of carbon monoxide and hydrogen cyanide in two unicellular N2-fixing cyanobacterial strains isolated from Korean coasts

Photobiological H2 from marine cyanobacterial strains is widely accepted to be an ideal clean and renewable energy source. Using the two Korean N2-fixing unicellular cyanobacterial strains (Cyanothece sp. KNU CB MAL-031 and Cyanothece sp. KNU CB MAL-058) and the Synechococcus sp. Miami strain BG043511 we performed flask-scale experiments to measure the effect of CO and HCN addition on photobiological H2 production. For the test, 1, 5, 10 and 30% v/v of CO in the N2 atmosphere was applied. Enhancement of H2 production was remarkable at 1–5% concentration range of CO addition. At CO concentrations over 5% no further cost-effective enhancement of H2 production was detectable, which suggests to us that 1–5% CO addition should be adopted for practical photobiological H2 production by the cyanobacterial strains. Maximum enhancement of the photobiological H2 production by CO additions was 2–6 times over the control flasks without CO. When 3 ppm of HCN was injected into the cell suspension of BG043511, the enhancement of hydrogen production was 50–60% of that under 5% CO. Present result implies the possible recycling of waste CO and HCN for the enhancement of the photobiological H2 production using marine cyanobacterial strains.

Two new species of benthopelagic Stephos (Copepoda, Calanoida, Stephidae) from Korea

Abstract Two new species of benthopelagic copepods of the genus Stephos T. Scott, 1892, belonging to the family Stephidae G.O. Sars, 1902, are described based on specimens collected in the stagnant water flooding the burrows excavated by ocypodid crabs in two intertidal mud-flats, and from near-bottom shallow waters in Korea, respectively. They can be easily diagnosed based on the ornamentation of both the female genital double-somite and genital operculum; the morphology of the distal segment of the male right P5; the presence/absence of a tiny pointed process on the distomedial angle of second segment of female P5; and the condition (seta or spine) of the lateral armature element on the distal segment of female fifth legs, among other features. This is one of the few cases reported of calanoid copepods living as commensals of other invertebrates, and raises to six the number of members of the genus reported from Asia. This is also the first record of the family Stephidae in Korea.

First Investigation of Microbial Community Composition in the Bridge (Gadeok Channel) between the Jinhae-Masan Bay and the South Sea of Korea

Microbial community composition varies based on seasonal dynamics (summer: strongly stratified water column; autumn: weakly stratified water column; winter: vertically homogeneous water column) and vertical distributions (surface, middle, and bottom depths) in the Gadeok Channel, which is the primary passage to exchange waters and materials between the Jinhae-Masan Bay and the South Sea waters. The microbial community composition was analyzed from June to December 2016 using 16S rRNA gene sequencing. The community was dominated by the phyla Proteobacteria (45%), Bacteroidetes (18%), Cyanobacteria (15%), Verrucomicrobia (6%), and Actinobacteria (6%). Alphaproteobacteria (29%) was the most abundant microbial class, followed by Flavobacteria (15%) and Gammaproteobacteria (15%) in all samples. The composition of the microbial communities was found to vary vertically and seasonally. The orders Flavobacteriales and Stramenopiles showed opposing seasonal patterns; Flavobacteriales was more abundant in August and December while Stramenopiles showed high abundance in June and October at all depths. The genus Synechococcus reached extremely high abundance (14%) in the June surface water column, but was much less abundant in December water columns. Clustering analysis showed that there was a difference in the microbial community composition pattern between the strongly stratified season and well-mixed season. These results indicate that the seasonal dynamics of physicochemical and hydrologic conditions throughout the water column are important parameters in shaping the microbial community composition in the Gadeok Channel.

New polymorphic microsatellite markers derived from hemocyte cDNA library of Manila clam Ruditapes philippinarum challenged by the protozoan parasite Perkinsus olseni

Manila clam Ruditapes philippinarum is one of the most important benthic animals in the coastal north Pacific region, where clam populations have been mixed genetically through trade and aquaculture activities. Accordingly, identification of the genetically different clam populations has become one of the most important issues to manage interbreeding of the local and introduced clam populations. To identify genetically different populations of clam populations, we developed 11 expressed sequence tag (EST)-microsatellite loci (i.e., simple sequence repeat, SSR) from 1,128 clam hemocyte cDNA clones challenged by the protozoan parasite Perkinsus olseni. Genotype analysis using the markers developed in this study demonstrated that clams from a tidal flat on the west coast contained 6 to 19 alleles per locus, and a population from Jeju Island had 4 to 20 alleles per locus. The expected heterozygosity of the 2 clam populations ranged from 0.472 to 0.919 for clams from the west coast, and 0.494 to 0.919 for clams from Jeju Island, respectively. Among the 11 loci discovered in this study, 7 loci significantly deviated from the Hardy-Weinberg equilibrium after Bonferroni correction. The 5 loci developed in this study also successfully amplified the SSRs of R. variegatus, a clam species taxonomically very close to R. philippinarum, from Hong Kong and Jeju Island. We believe that the 11 novel polymorphic SSR developed in this study can be utilized successfully in Manila clam genetic diversity analysis, as well as in genetic discrimination of different clam populations.

A new species of Prohatschekia Nunes-Ruivo, 1954 (Siphonostomatoida: Hatschekiidae) from the scorpaenid fish, Scorpaena neglecta Temminck & Schlegel, 1843 (Scorpaeniformes: Scorpaenidae), in Korean waters

A new species of parasitic copepod, Prohatschekia pseudocremouxi sp. nov. is described based on adult females collected from the gills of the scorpaenid fish, Scorpaena neglecta Temminck & Schlegel, 1843 caught in Korean waters. The new species is most closely related to P. cremouxi Nunes-Ruivo, 1954, but differs from it by the following combination of characters in the adult female: the size of the trunk which is about 3.7 times as long as cephalothorax; the short and strongly curved antennary claw; and the distal segment of the maxilla is tipped with a simple seta. This discovery raises the number of nominal species in Prohatschekia Nunes-Ruivo, 1954 to eight and represents the first record of the genus in Korea.

Description of postembryonic developmental stages of Pseudodiaptomus koreanus Soh, Kwon, Lee & Yoon, 2012 (Copepoda, Calanoida, Pseudodiaptomidae)

The complete postembryonic development of Pseudodiaptomus koreanus Soh, Kwon, Lee & Yoon, 2012 (Copepoda, Calanoida) comprises six naupliar and six copepodid stages of which the last is the adult. The descriptions were based on laboratory-reared nauplii and copepodids and also on copepodids collected by plankton net, all sourced from the Seomjin River estuary in southern Korea. Nauplius and copepodid stages of P. koreanus are very similar to those of the previously described species of Pseudodiaptomus . However, of all the characteristics, it is the shape and number of setae on the terminal segments of the antennules in the late naupliar stages, and the shape and somites of the body and the segmentation and number of setae of the exo- and endopods of the swimming legs from copepodid stages I to V, which are most useful in reconstructing relationships among the eight Pseudodiaptomus spp. reared until now.

Measurement and Analysis of Three-Dimensional Shape Variations of Microalgae Based on a Digital Holographic Microscopy for Prediction of the Spread Point of Red Tide

Thus far, a general approach to prevent the occurrence of the red tide phenomena and to minimize its resultant damage is to predict the spread point of the red tide. For that, conventionally a set of microalgae are periodically sampled from several shore areas and their numbers of microalgae per unit area are simply counted to predict the threshold level of the spread point of the red tide. However, this approach cannot foresee a decisive symptom for spreading of the red tide in advance. Accordingly, in this paper, we propose a novel approach for accurate prediction of the spread point of red tide by measuring and analyzing the three-dimensional (3-D) volume information of the microalgae with the digital holographic microscopy (DHM). This volume information of the microalgae can be converted into the thickness information through digital holographic reconstruction. With these thickness data, the volume variations of microalgae in time can be finally measured and analyzed. Experiments with several samples of microalgae may confirm the feasibility of the proposed method in the practical application.