Ju-Hyoung Kim

Enhanced Production of Oceanic Dimethylsulfide Resulting from CO2-Induced Grazing Activity in a High CO2 World

Oceanic dimethylsulfide (DMS) released to the atmosphere affects the Earths radiation budget through the production and growth of cloud condensation nuclei over the oceans. However, it is not yet known whether this negative climate feedback mechanism will intensify or weaken in oceans characterized by high CO(2) levels and warm temperatures. To investigate the effects of two emerging environmental threats (ocean acidification and warming) on marine DMS production, we performed a perturbation experiment in a coastal environment. Two sets of CO(2) and temperature conditions (a pCO(2) of ∼900 ppmv at ambient temperature conditions, and a pCO(2) of ∼900 ppmv at a temperature ∼3 °C warmer than ambient) significantly stimulated the grazing rate and the growth rate of heterotrophic dinoflagellates (ubiquitous marine microzooplankton). The increased grazing rate resulted in considerable DMS production. Our results indicate that increased grazing-induced DMS production may occur in high CO(2) oceans in the future.

Adaptations of a green tide forming Ulva linza (Ulvophyceae, Chlorophyta) to selected salinity and nutrients conditions mimicking representative environments in the Yellow Sea

Abstract: The massive green tide species Ulva linza undergoes an apparent rafting in a counterclockwise direction in the Yellow Sea from Jiangsu Province, China, to the west coast of Korea. During this dispersal, it undergoes development from early life history stages to senescence and experiences extensive salinity and nutrient gradients. We investigated the physiological responses of different developmental stages of U. linza to three representative environmental conditions that mimicked (1) a brackish environment at salinity 10 (S = 10) and 200 μM NO3−, (2) an inshore environment at S = 30 and 200 μM NO3−, and (3) an offshore environment at S = 30 and 4 μM NO3−. Chlorophyll a fluorescence of the early development stages (spores and germlings) of U. linza was measured using pulse amplitude modulation fluorometry to determine their photosynthetic efficiency. In addition, the photosynthesis and respiration rates of adult thalli were measured using chamber incubation. Within two hours of release, spores showed no difference in photosynthetic performance in the three conditions. Subsequently, the photosynthesis of germlings was enhanced at high-nutrient conditions regardless of salinity, suggesting that brackish and inshore waters are suitable nursery areas for early development. The adult thalli in the brackish environment showed two and three times higher growth rates than in the inshore and offshore environments, respectively. The adult thalli experienced synergistic effects of high nutrients and low salinity on photosynthesis that facilitated rapid growth in brackish environments. Overall, we suggest that brackish areas facilitate the initiation of blooms of U. linza, and the subsequent movement of floating fronds from estuaries to the inshore and then the offshore provides a continuous nutrient inoculum that maintains the population in the offshore environment.

Using a Digital Echosounder to Estimate Eelgrass (Zostera marina L.) Cover and Biomass in Kwangyang Bay

Eelgrass beds are very productive and provide nursery functions for a variety of fish and shellfish species. Management for the conservation of eelgrass beds along the Korean coasts is critical, and requires comprehensive strategies such as vegetation mapping. We suggest a mapping method to spatial distribution and quantify of eelgrass beds using a digital echosounder. Echosounding data were collected from the northeast part of Kwangyang Bay, on the south of Korea, in March, 2007. A transducer was attached to a boat equipped with a DGPS. The boat completed a transect survey scanning whole eelgrass beds of 11.7 km2 with a speed of 1.5-2 m s-1 (3-4 knot). The acoustic reflectivity of eelgrass allowed for detection and explicit measurements of canopy cover and height. The results showed that eelgrass bed was distributed in depth from 1.19 to 3.6 m (below MSL) and total dry weight biomass of 4.1 ton with a vegetation area of 4.05 km2. This technique was found to be an effective way to undertake the patch size and biomass of eelgrass over large areas as nondestructive sampling.

Anti-inflammatory Effects of Polyphenol Extracts from Ulva linza (Ulvophyceae, Chlorophyta)

ObjectiveUlvoid macroalgal blooms are frequently observed in coastal oceans worldwide. Because of the very high potential for outbreaks of these blooms, many researches have recently become focused on the utilization of natural products extracted from these otherwise commercially worthless seaweeds. The green-tide forming alga, Ulva linza, in particular, is known for its high antioxidative effects, however, the anti-inflammatory effects of its main constituents have not been thoroughly studied.MethodsTo address this knowledge gap, TNBS-induced colitis mice were administered with an ethanol extract from U. linza, which reduced their colitis and allowed us to observe the anti-inflammatory effects.ResultsAfter reducing colitis, differences between two groups of mice, one which was administered with the U. linza extract and the other without the extract, were observed in comparison to budesonide. These anti-inflammatory effects of the U. linza extract were further confirmed in LPS induced RAW 264.7 cells.ConclusionTogether, our results demonstrate that polyphenol extracted from U. linza is the component that exhibits the anti-inflammatory effects in TNBS-induced colitis mice, and suggests that it could be used as a potential natural therapeutic agent for the prevention of inflammatory bowel disease (IBD).

Elevated temperature and changed carbonate chemistry: effects on calcification, photosynthesis, and growth of Corallina officinalis (Corallinales, Rhodophyta)

Abstract: Recent ecophysiological studies of coralline algae have highlighted the effects of several environmental concerns, such as acidification and warming of the worlds coastal oceans. Among these, elevated temperature might be the most critical environmental factor affecting rocky benthic communities, where coralline algae tend to dominate the habitat. This study was conducted to investigate changes in photosynthesis, calcification, and growth of the geniculate coralline alga Corallina officinalis after 7 d of acclimation to four temperature conditions (13, 18, 23, and 28°C). Calcification rates decreased with increasing temperature in the light, although growth of C. officinalis did not differ considerably under different temperatures. Furthermore, although photosynthesis was largely unaffected by increasing temperature, respiration increased significantly under the highest temperature. These physiological responses are strongly related to the carbonate chemistry of seawater, which is itself affected by elevated temperature. Our results also indicate that C. officinalis exhibits physiological tolerance to a wide range of temperatures, even when increased by more than 10°C above ambient temperature of 18°C. Consequently, if noncalcareous macroalgae are negatively affected by higher temperatures, the ability of C. officinalis to acclimate to these conditions could cause it to become a more dominant species of rocky macroalgal habitats as ocean temperatures continue to rise.

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.