Suk Min Yun

Morphological Characteristics of Four Species in the Genus Skeletonema in Coastal Waters of South Korea

Most Skeletonema species have been identified under the name of S. costatum. To assess the morphological species diversity in the genus Skeletonema, we surveyed the nine localities in the coastal waters of South Korea. The light microscopy (LM) and scanning electron microscopy (SEM) observations in this study showed that ultrastructural features of genus Skeletonema discriminated among four species: S. dohrnii Sarno & Kooistra, S. marinoi Sarno & Zingone, S. subsalsum (Cleve) Bethge, and S. tropicum Cleve. In S. dohrnii, cell diameters were 3-6 μm and the pervalvar axes were 13-19 μm. One or two partial chloroplasts were visible in a cell. Cells of S. marinoi were 4-10 μm and the pervalvar axes were 8-18 μm. Each cell contained one chloroplast. Cells of S. subsalsum which contained 1-2 chloroplasts were 8-13 μm and the pervalvar axes were 11-20 μm. Cells of S. tropicum were 10-18 μm and the pervalvar axes were 4-9 μm. 2-4 chloroplasts were seen in each cell. Tip width of fultoportula in S. dohrnii and S. marioni was flared and flat, but that in S. subsalsum and S. tropicum was narrow. Morphological groups among them, S. dohrnii and S. marinoi were the most widely distributed in all seasons, while S. tropicum was only occurred in a summer season.

Critical criteria for identification of the genus Chaetoceros (Bacillariophyta) based on setae ultrastructure. II. Subgenus Hyalochaete

Abstract: Our objective was to select setae ultrastructure characteristics as identification criteria for Chaetoceros subgenus Hyalochaete. We sampled 53 Korean coastal water locations and three Chukchi Sea, Arctic Ocean sites, and we studied 22 species using light microscopy and scanning electron microscopy. We selected 12 criteria for species-specific identification: (1) point of fusion of the sibling setae, (2) spine form, (3) poroid shape, (4) spine arrangement, (5) poroid arrangement, (6) number of poroid rows per μm along the setae, (7) special intercalary setae, (8) connecting bridge-like structure on the basal part of the intercalary setae, (9) siliceous capilli on the basal part of the setae, (10) setae cross-sectional shape, (11) silicification of the setae wall and (12) direction of setae to the chain axis. Using these criteria, we constructed a dichotomous key to aid species-specific identification in the subgenus Hyalochaete.

Can the algicidal material Ca-aminoclay be harmful when applied to a natural ecosystem? An assessment using microcosms

We assessed the ability of an artificial clay (Ca-aminoclay) to suppress harmful algal bloom species (HABs) such as Cochlodinium polykrikoides and Chattonella marina and investigated the ecological responses in the closed and open microcosm systems. The Ca-aminoclay induced rapidly and selectively cell lysis in the HABs. However, applying Ca-aminoclay could cause adverse impacts in terms of biological and environmental changes. The bacterioplankton abundance increased and then, the abundances of heterotrophic nanoflagellates and ciliates increased rapidly. Extremely poor environmental conditions such as increase in nutrients and development of anoxic conditions were sustained continuously in a closed system, while the environmental conditions in open systems deteriorated before recovering to the initial conditions. We evaluated the potential for the occurrence of a bloom of another phytoplankton after HABs had been controlled using the Ca-aminoclay. The Ca-aminoclay controlled blooms of Chattonella marina in mixed cell cultures containing a Tetraselmis chui. However, T. chui increased over time and then bloomed. Therefore, caution should be taken when considering the direct application of Ca-aminoclay in natural environments even though it offers the rapid removal of HABs.

Species diversity of the genus Thalassiosira (Thalassiosirales, Bacillariophyta) in South Korea and its biogeographical distribution in the world

Abstract: Thalassiosira species are an important component of phytoplankton populations, and most species are considered cosmopolitan. Many authors have investigated the diversity of Thalassiosira species in order to understand their ecological roles in local areas. Our regional taxonomic study revealed the presence of 44 Thalassiosira species at 124 sites in Korean coastal waters. Of these, 14 species are newly reported in Korean waters and are described in detail with external and internal valve illustrations. Some morphologically confused taxa, such as the Thalassiosira s.s. group, T. curviseriata/T. tealata, T. simonsenii/Planktoniella blanda and T. proschkinae/T. spinulata, are clearly distinguished using additional morphological criteria. In addition, the full biogeographical distribution of Thalassiosira is described and compared with the Korean species. Korean waters seem to be the ‘Maginot Line’ for the cold- and warm-water Thalassiosira species. Knowledge of Thalassiosira species diversity will increase with more intensive work in relatively little-studied regions, such as the Indo-Pacific and tropical Atlantic Oceans.

The relationship between epilithic diatom communities and changes in water quality along the lower Han River, South Korea

Epilithic diatom communities were sampled every two weeks from February 2001 to February 2002 at three sites in the lower Han River (LHR), South Korea, to investigate how epilithic diatom communities reflected longitudinal gradients in environmental quality measures. The water quality in the LHR differed between the rainy and dry seasons and also varied at different sites according to levels of pollution. The epilithic diatom communities responded to changes in the aquatic environment and hydrological characteristics. There were few predominant diatom species during the rainy season, and they were found at lower concentrations than in the dry season because of the high current velocities caused by heavy rainfall. The predominant species at the three study sites in the LHR were different because of the effects of eutrophication gradients. Cocconeis placentula, Diatoma vulgaris, and Nitzschia dissipata were dominant at site 1 (clean to nutrient-rich conditions). Fragilaria capucina var. gracilis and Gomphonema parvulum were dominant at site 2 and their growth was accelerated by the moderately-nutrient-rich conditions. Luticola goepperitnana, N. palea, small Nitzschia spp., and small Navicula spp. were dominant in the most polluted pools at site 3. We conclude that the LHR has a water quality gradient along its course, and that this causes marked changes in the epilithic diatom species compositions found along the river. The results confirm that epilithic diatoms are important bioindicators for assessing ecological quality in the LHR.

Fossil diatom assemblages as paleoecological indicators of paleo-water environmental change in the Ulleung Basin, East Sea, Republic of Korea

The fossil diatom assemblage record from two sediment cores obtained from the Ulleung Basin, East Sea, Republic of Korea, revealed changes in the diatom assemblage zones in PG1 and PD3 core samples. The two sediment cores were δC14 dated and approximately represented the late Pleistocene–Holocene. The analysis of age zones in the PG1 core and PD3 core was assessed based on the frequency of variations, and occurrences of biostratigraphical fossil diatom species. During the Last Glacial Maximum (LGM), the sea level was lower than that at present and the Ulleung Basin became isolated from the Pacific Ocean. As a result, there would have been a limited Tsushima Warm Current (TWC) influence, and salinity would have decreased resulting in increased freshwater and coastal diatoms. The distribution pattern of diatoms presented in the cores was associated with changes in water temperature and salinity and the adding of terrigenous material brought about by the input of freshwater. Changes in the abundance of a tychopelagic diatom, Paralia sulcata, reflected the effect of the water currents. Diatom temperature (Td) values and the ratio of centric/pennate diatoms provided evidence of limited influences of the TWC and freshwater inflow. It is thought that all assemblage zones were influenced by the TWC, which had an important effect on the distribution and composition of fossil diatoms.