Kyoungsoon Shin

Influence of food quality on egg production and viability of the marine planktonic copepod Acartia omorii

Egg production, egg viability and fecal pellet production were determined for individual Acartia omorii, which were fed diets of two species of diatoms (Skeletonema costatum and Phaeodactylum tricornutum ) and three species of dinoflagellates ( Scrippsiella trochoidea, Heterocapsa triquetra and Cochlodinium polykrikoides ). Diets were analyzed for fatty acid content as an indicator of food quality. Depending on the diet, egg production of A. omorii varied over time, diminishing with some diets (S. trochoidea, C. polykrikoides, P. tricornutum ). This rate of reduction was much more rapid for a diet of C. polykrikoides, which caused egg production to decrease to ca. 2.4 eggs f 1 d 1 in only four days. As for all diets, egg viability was high at the beginning but with the C. polykrikoides and P. tricornutum diets, it rapidly decreased with time. Fecal pellet production also varied with time, depending on the diet. Egg production rate was closely correlated with fecal pellet production. There was no direct relationship between egg viability and egg production rate, but both egg production and viability were affected by the nutritional quality of food. Egg viability was also highly dependent on the composition of fatty acids in the eggs. Egg viability showed positive correlation with the ratio of ω 3:ω 6 groups among egg fatty acids, and negative correlation with the ratio of 20:5 (n3) : 22:6 (n3). While comparing several diets, egg production rate was higher on diets (H. triquetra and S. trochoidea) containing ample amounts of essential fatty acids such as 18:4 (n3) and 22:6 (n3). The results suggest that fertility of A. omorii was dependent upon the quality of the food, and dinoflagellate diets, with the exception of C. polykrikoides, were preferable to diatom diets. uf6d9 2003 Elsevier Ltd. All rights reserved.

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.

Tintinnid species as biological indicators for monitoring intrusion of the warm oceanic waters into Korean coastal waters

This study examined seasonal and annual occurrences of warm oceanic tintinnid species in southern Korea coastal waters. The indicative species of tintinnids was monitored using three approaches: monitoring from cruises traveling from the warm pool in the western North Pacific to the Korea Strait; biweekly or monthly monitoring in the Korea Strait; and daily monitoring in the nearshore water. Annual pulses of warm oceanic indicator species were regularly observed in the Korea Strait. In September 2008 recorded a maximum species number of warm water indicators, a representative species for warm oceanic waters, Climacocylis scalaroides was simultaneously detected in the nearshore water as well as the Korea Strait. The result indicates that the greater warm water extension into Korean coastal areas was in September 2008. Sharp declines in species diversity were observed in the transitional area between neritic and Kuroshio zone in East China Sea (ECS). Epiplocyloides reticulata, reported previously as a Kuroshio indicator, was considered an ECS indicator species, as it was undetected in the western North Pacific central zone but was found abundantly in the ECS. Tintinnid species can be used as biological indicators to detect the inflow of warm oceanic waters into Korean coastal waters.

Phytoplankton viability in ballast water from international commercial ships berthed at ports in Korea

We investigated the viability of phytoplankton from ballast water of international commercial ships berthed at the ports of Ulsan and Onsan, Korea. The incubation conditions used were temperatures of 13 degrees C to represent ambient water and 20 degrees C to represent the thermal optimum, as well as nutrients in ballast water, shipside water, and F/2 medium. Phytoplankton in new (approximately 7 days) and old (20 and 2 days) ballast water survived when incubated under the nutrients typical of shipside water and F/2 medium at 13 degrees C and 20 degrees C. Colonization process was mostly dominated by Skeletonema costatum, Cylindrotheca closterium and pennate diatoms (<10 microm in diameter). S. costatum and C. closterium were persistent during incubation time, whereas pennate diatoms dominated in the three types of media from doubling to last phase of growth. This study showed that bloom-forming and pennate diatoms appear to be the species most likely to become successfully established in the two ports.

Algicidal activity of the thiazolidinedione derivative TD49 against the harmful dinoflagellate Heterocapsa circularisquama in a mesocosm enclosure

To assess the algicidal effects of the thiazolidinedione derivative TD49 on the unarmored dinoflagellate Heterocapsa circularisquama and to evaluate the response of the planktonic community and the environment to this chemical, we undertook mesocosm (1,300xa0L) and small-scale experiments. The reduction ratio for H. circularisquama in each experiment was dependent on the concentration of TD49. At a TD49 concentration >0.4xa0μM, the abundance of H. circularisquama decreased by 99xa0% in the small-scale experiment and by 84xa0% in the mesocosm during the initial 2xa0days. At 0.2xa0μM TD49, the abundance of H. circularisquama decreased by up to 85xa0% in the small-scale experiment, whereas the abundance in the mesocosm increased, implying the absence of an algicidal effect. The decrease in planktonic organisms, including H. circularisquama, following TD49 treatment was correlated with abrupt declines in culture pH and dissolved oxygen concentration. Following addition of TD49, there was a significant increase in the abundance of diatoms and cryptophyta species, and after 8xa0days, the dominant species in the TD49 treatments shifted to small pennate diatoms including Cylindrotheca and Entomoneis species. The growth of some species among the zooplankton community was promoted at low TD49 concentrations (≤0.4xa0μM), whereas high concentrations (≥1.0xa0μM) had a negative effect. This study demonstrates that TD49 is an effective agent for the control for H. circularisquama blooms and that large-scale mesocosms play a crucial role in assessing the application of algicides such as TD49 in natural environments.

Dense winter bloom of the dinoflagellate Heterocapsa triquetra below the thick surface ice of brackish Lake Shihwa, Korea

We investigated the seasonal abundance of the dinoflagellate Heterocapsa triquetra (Ehrenberg) F. Stein, as well as the relevant in situ environmental factors, in brackish Lake Shihwa, Korea. We also examined the growth rates and morphological characteristics of the species in laboratory cultures. In the field, the population densities of H.u2003triquetra remained at low levels from late spring to early summer, and then completely disappeared from August to November 2007. Interestingly, a dense bloom of H.u2003triquetra appeared below the ice surface on 17 January 2008; identities of the cells were confirmed by rDNA sequence comparisons. The second peak reached a density of 672u2003×u2003 103u2003cellsu2003L−1 on 28 March 2008, at a water temperature of 9.1°C. Laboratory experiments showed that growth rates of H.u2003triquetra increased with incremental temperature increases within the range of 10 and 20°C. The highest growth rate reached by H.u2003triquetra was 0.62u2003d−1 at 20°C with a salinity of 30. Above 25°C, the dinoflagellate was unable to grow between salinities of 10 and 15, and reached only relatively low growth rates (<0.12u2003d−1) under other salinity conditions. However, under continuous cultures at 5°C and 8°C, H.u2003triquetra cells retained its growth capability for more than 12 days, implying that H.u2003triquetra can survive and grows even at very low temperatures. The equivalent spherical diameter (ESD) of H.u2003triquetra did not change markedly between 10 and 25°C, but the equivalent spherical diameter was significantly different at 5°C. The cell volume buildup of H.u2003triquetra at low temperatures is one of the important survival strategies to overcome the harsh environmental conditions. These characteristics make H.u2003triquetra a consistently dominant dinoflagellate in Lake Shihwa during the cold winter season.

Spatial and Temporal Trends in Water Quality in Response to Sewage Discharge in Masan and Hangam Bays, Korea

Abstract This study investigated the spatial and seasonal variations of nutrients, chlorophyll-a (Chl-a), particulate organic carbon, and dissolved oxygen at four stations around Masan Bay from February 2004 to February 2006. Nutrients showed large spatial and seasonal variations in the study area. Dissolved inorganic nitrogen and dissolved silicate concentrations were highest at inner Masan Bay, which was ascribed to the largest inputs of both nutrients from the lands among four stations. Dissolved inorganic phosphorus concentrations are highest at Hangam Bay, where a fertilizer plant caused serious soil pollution with the by-products of phosphate rocks. The extremely high Chl-a concentrations (>60 µg L−1) were observed at inner Masan Bay in July and attributed to the plentiful nutrients, high water stability, and longer residence time at this area during summer. Surface Chl-a concentrations displayed large seasonal variations at all stations, with high values in summer and low values in fall and winter. The lower Chl-a concentrations in fall and winter may be due to strong vertical mixing, which could transport phytoplankton below the euphotic depth, and as a result, constrained phytoplankton growth. Particulate organic carbon–to–Chl-a ratios varied from 59.8 to 121, with large spatial variation and small seasonal change. Hypoxia (<2 mg L−1) was observed at inner and outer Masan and Hangam bays during summer. Outer Masan Bay showed more severe hypoxia than inner Masan Bay in summer 2004 and 2005, which was probably because of the higher organic contents at the bottom sediments and deeper water depth. Despite construction of the Masan and Jinhae wastewater treatment plants, Masan and Hangam bays still received high loading of nutrients, and serious eutrophication was still observed at these bays.

Algicidal effects of yellow clay and the thiazolidinedione derivative TD49 on the fish-killing dinoflagellate Cochlodinium polykrikoides in microcosm experiments

In order to evaluate the potential to control the fish-killing dinoflagellate Cochlodinium polykrikoides, we compared the algicidal effects of the thiazolidinedione derivative TD49 with those of yellow clay in 10-L microcosms. The responses of higher trophic level marine organisms and microbial loop communities to the algicide were also evaluated. In the yellow clay treatments, the concentration of C. polykrikoides was slightly reduced at day 1 of the experiment but remained higher than that of the control, suggesting that the reduction ratio of C. polykrikoides was <20xa0%. In the 0.8-μM TD49 treatment, the abundance of C. polykrikoides declined by 98xa0% 1xa0day following the addition of the algicide. The algicide did not affect nontarget algae including Chaetoceros spp., Skeletonema spp., Cylindrotheca spp., and other species. In all microcosms, bacterial abundance increased abruptly after day 1, then declined over the next 2xa0days as a result of predation by heterotrophic nanoflagellates and the small protozoan Uronema sp. Predation by the large protozoan species Euplotes sp. on Uronema sp. gradually increased with increasing incubation time in the TD49 treatment. Zooplankton were particularly affected by the environmental changes that occurred in the microcosms following collapse of the C. polykrikoides populations. Striped beak perch were not affected by the yellow clay treatments and concentrations of TD49u2009<u20092.0xa0μM. The results suggested that the yellow clay has little effect on C. polykrikoides, whereas the algicide TD49 is effective in controlling the harmful alga. The results imply that the algicide has positive effects on natural microbial communities and is not toxic to nonharmful algae and higher trophic level marine organisms.

Summer pattern of phytoplankton distribution at a station in jangmok bay

Daily changes in phytoplankton abundance and species composition were monitored from July to September 2003 (n=47) to understand which factors control the abundance at a station in Jangmok Bay. During the study, the phytoplankton community was mainly composed of small cell diatoms and dinoflagellates, and the dominant genera wereChaetoceros,Nitzschia, Skeletonema andThalassionema. Phytoplankton abundance varied significantly from 6.40x104 to 1.22x107 cells/l. The initially high level of phytoplankton abundance was dominated by diatoms, but replacement by dinoflagellates started when the N/P ratio decreased to < 5.0. On the basis of the N/P and Si/N ratios, the sampling period could be divided into two: an inorganic silicate limitation period (ISLP, 14th July-12th of August) and an inorganic nitrogen limitation period (INLP, 13th of August - the end of the study). Phosphate might not limit the growth of phytoplankton assemblages in the bay during the study period. This study suggests that phytoplankton abundance and species composition might be affected by the concentrations of inorganic nutrients (N and Si), and provides baseline information for further studies on plankton dynamics in Jangmok Bay.

Effect of Thermal Stratification and Mixing on Phytoplankton Community Structure in the Western Channel of the Korea Strait

The profile of a fixed site at station M (34.77˚N, 129.13˚E) in the Korea Strait was studied from March 2006 to February 2007. The aim was to understand the relationship between the annual thermal stratification pattern and seasonal variation in phytoplankton community structure. Physicochemical factors including temperature, salinity and nutrient concentrations, which strongly influence the proliferation and diversity of phytoplankton, were measured. The study period was divided into three due to the characteristic of thermohaline structures; mixed Ⅰ (March-May 2006), stratified (June-November 2006) and mixed Ⅱ (December 2006-Feburuary 2007). Diatoms dominated during the mixed Ⅰ (89%) and Ⅱ (48%) periods, while nanoplankton group occupied over 83% of total population during the stratified period. The dominant species during the mixed Ⅰ and Ⅱ was Chaetoceros socialis (47% and 29%, respectively), while during the stratified period Gyrodinium sp. (4%) was the most dominant. Averaged total chl a concentrations during the mixed Ⅰ and Ⅱ periods were 0.61 ㎎ m?³ and 0.72 ㎎ m?³, respectively, which were at least two-fold higher than that during the stratified period (0.30 ㎎ m?³). The vertical mixing and convection process of the water column induced nutrient supply from the bottom layer to the euphotic zone. It also led to the dominance of diatoms during the mixed periods, whereas small phytoplankton prevailed over large phytoplankton as stratification blocked the upward movement of nutrients to subsurface during the stratified period. During the mixed Ⅰ and Ⅱ periods, microplanktonic chl a dominated concentrations (50% and 48%, respectively), while picoplanktonic chl α occupied over 37% of total chl a during the stratified period.