• Ocean and Polar Research
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• v.40 no.1
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• pp.15-22
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• 2018

In the present study, we investigated temporal variation in the reproductive effort and biochemical contents in adult Manila clam Ruditapes philippinarum at Shi-Heung-Ri beach on the east coast of Jeju Island. Gonad-somatic index (GSI), a ratio of the egg mass to the total biomass determined using ELISA increased dramatically from late May to June (7.1% to 19.5%). In mid-July, GSI dropped to 15.1%, indicating spawning on a small scale during this period. GSI also declined dramatically from late August (15.5%) to September (4.3%), suggesting that massive spawning occurred during this period. A positive correlation was observed between clam size and potential fecundity, while potential fecundity ranged between 1.19-8.40 million eggs/clam. Total proteins and lipids in the tissue increased from late spring to mid-summer, coinciding with an increase in GSI. Protein, lipid and carbohydrate contents in the tissue were lowest in January, indicating that clams were suffering from poor nutritional circumstances, which may be associated with poor food supply from the environment. Monthly increase and/or decrease in the body weight were closely related to gonad maturation and subsequent spawning, which was also linked to temporal changes in the contents of protein, lipid and carbohydrates in the tissue.

• ALGAE
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• v.33 no.4
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• pp.341-349
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• 2018

Sargassum horneri is edible brown seaweed abundant along the coasts of Jeju Island, South Korea. In addition to the native S. horneri population, a large amount of S. horneri has been found to invade Jeju Island from the east coast of China. Thus, S. horneri of both Korea (SK) and China (SC) strains now inhabits along with the shore of Jeju Island and have become a threat to the coastal biodiversity. However, they could be used in obtaining functional ingredients for industrial level applications provided an optimized cost effective strategy. In the present study, we compared SK and SC strains for the extraction efficiency, components, antioxidant, and anti-inflammatory properties of 80% methanolic extracts and their partially purified fractions. According to the results, two strains indicated similar bioactive properties such as DPPH and alkyl radical scavenging activity as well as anti-inflammatory activities on lipopolysaccharide-stimulated RAW 264.7 cells. The yield of 80% methanol extract from SC was higher than SK. However, the yields of the ethyl acetate and chloroform fractions from SK were higher than those of SC strain. The major peaks in the high-performance liquid chromatography chromatograms, which was identified as Apo-9 fucoxanthinone, indicated that both methanolic extracts of SK and SC contains major target peaks but with different amounts. This study might be useful for developing functional materials from SC and SK in future.

• ALGAE
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• v.19 no.3
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• pp.235-245
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• 2004

A study on seasonal characteristics of phytoplankton dynamics and environmental factors was carried out at four stations including Mara-do and U-do located in the western and eastern coast of Jeju Island in southern Korea from April 2003 to March 2004. Out of 101 phytoplankton species identified, 84 belong to Bacillariophyceae, 9 Dinophyceae, 6 phytoflagellates and 2 coccolithophorids, and the highest value of species diversity was observed in April. Phytoplankton was more abundant at the western coast than at the eastern coast from March to September and its highest abundance was 49.24 ${\times}$ 10$^3$ cells L$^{-1}$ at Mara-do in July. The pennate diatoms were more abundant at the western coast than at the eastern coast with the highest abundance of 38.75 ${\times}$ 10$^3$ cells L$^{-1}$ at Mara-do in July, and during this period Nitzschia longissima contributed 68.5% of the total phytoplankton abundance. Naviculaceae was more abundant at Gosan (western coast) in November when Stauroneis membranacea represented 80.1% of the abundance. Leptocylindrus dances contributed 49.4% of the abundance at U-do in November. Dinophyceae was more abundant at U-do in August. Water temperature and pH fluctuated from 11.7${^{\circ}C}$ to 27.1${^{\circ}C}$ and from 7.31 to 8.70, respectively. Water temperature of Mara-do was about 1-2${^{\circ}C}$ higher than the other stations. Salinity varied from 30.4 to 35.0 psu with the minimum in rainy season and the maximum at the end of winter. The concentration of NH$_4$-N, NO$_3$-N, NO$_2$-N, PO$_4$-P and SiO$_2$-Si ranged 0.07-6.79, 1.0-62.0, 1.0-8.0, 1.0-7.0 and 7.0-191.0 $\mu$g-at L$^{-1}$, respectively. Chlorophyll a concentrations varied from 0.10 to 1.17 $\mu$g L$^{-1}$. NH$_4$-N concentrations were high at U-do from May to December, and at Mara-do from January to February. The high concentrations of NO$_3$-N were found at Mara-do from June to September and at U-do from January to May. The effects of various physicochemical parameters on the seasonal distribution and succession of phytoplankton population suggest that there is a classical pattern of phytoplankton dynamics in Jeju coastal waters.

• Korean Journal of Environmental Biology
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• v.35 no.3
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• pp.319-328
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• 2017

The continuous exploration in deep seawater from Korea makes us lead the discovery of ancient Chlorophyta, Palmophyllum, in the Korean coast. The phylogenetic analyses of 18S rRNA and rbcL genes demonstrate that our specimens are Palmophyllum crassum (Naccari) Rabenhorst, recorded in Japan and clearly distinguished from P. umbracola from New Zealand and California, USA. Palmophyllum crassum grows in the subtidal region, 8-30 m deep, and has a crustose thallus which is closely adherent to substrates such as non-geniculate crustose coralline algae, sponge, shells, or rocks. P. crassum is composed of numerous spherical cells embedded in the gelatinous matrix. The discovery of this ancient green seaweed implies that the Korean coast is one of the hotspots of algal species diversity and has the suitable marine environment for algal speciation. We suggest the grounds to conserve the Korean coast environmentally as the biodiversity center of marine species by studying the phylogeny of seaweeds.

• Journal of Fisheries and Marine Sciences Education
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• v.27 no.2
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• pp.422-429
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• 2015

The purpose of this study is the improvement of the existing trolling hauler, which has only one wheel to wind a main line, for saving man power around the coast of Jeju island. The trolling hauler manufactured for a test performance consisted of the wheel part of a main line and the roller part of a leader line including labor-saving devices comprised of a friction clutch, a fastener and springs. Even though this existing electric hauler system is convenient to control the wheel speed and the winding direction, it is apt to cost high and to corrode quickly at sea. Therefore, to remove these negative elements and to operate rollers for hoisting a leader line of the trolling, hydraulic motors were used separately. As a result, according to using of labor-saving devices, the towing tension occurred in operating in fishing ground could be selected moderately without breaking of lines and the operating efficiency of the trolling hauler was verified.

• 한국해양학회지
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• v.21 no.3
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• pp.171-183
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• 1986

The amplitudes of the M2 tide recorded at Seoguipo and Jeju are 77.9cm and 70.1cm respectively, which differ by 7.8cm over a distance of 30km across the Jeju-Do. The difference is an example of the geographical variation of the tidal amplitude around the Jeju-Do, the larger amplitude being along its southern coast compared with that along its northern coast. This variation can be explained in terms of effects of an island on the wave propagation as modelled by Proudman(1914). A numerical experiment of the M2 tide around the Jeju-Do reproduces the basic pattern of the observed variation and results are consistent with the theory. Due to the rotation of the earth larger and smaller amplitudes result along the left-hand and right-hand coasts of an island for an observer facing the direction of the wave propagation in the northern hemisphere.

• Ocean and Polar Research
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• v.34 no.1
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• pp.65-71
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• 2012

Gambierdiscus toxicus, Adachi et. Fukuyo, is a benthic ciguatoxin-producing armored dinoflagellate, often attached to macroalgae. This organism is the primary causative agent of ciguatera fish poisoning which occurs in tropical and subtropical regions. However, regardless of the fact that the population of Gambierdiscus spp. has expanded to such temperate areas from sub-trophic and trophic areas, monitoring of G. toxicus has been lacking in the Korean coastal waters of temperate areas. This study was performed at the uninhabited Baekdo Islands off the southern coast of Korea and at Seopsom Island in the vicinity of Seogwipo, Jeju Province during April and May, 2011. Cell densities of Gambierdiscus spp. on macroalgae at Baekdo and Jeju Island ranged from zero to 56.4 cells $g^{-1}$. Maximum density was recorded on the brown alga Cladophora japonica at St. 3 of Jeju Island. In particular, the cell densities of Gambierdiscus spp. were influenced by the substrate characteristics of macroalgae. In the future, the continuous monitoring of toxic benthic dinoflagellate is necessary to predict and prevent ciguatera poisoning in Korean coastal waters.

• The Korean Journal of Malacology
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• v.32 no.1
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• pp.31-36
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• 2016

In the present study, we observed a unique association of the flat oyster, Ostrea denselamellosa obtained from a muddy substrate at Haechang Bay, the south coast of Korea in the spring of 2013. Fossilized or semi-fossilized veneriid clam shells, possibly Ruditapes philippinarum, were found adhering to the umbonal area of the flat oyster valves. This unique association of the flat oyster shells with the fossilized clam shells suggested that the flat oyster larvae utilized the clam shells as substrate during settlement. Since availability of clam shells in the muddy subtidal environment is limited, this unique substrata for the flat oyster larvae may limit recruitment of the flat oysters in the bay.

• 한국해양학회지
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• v.23 no.2
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• pp.62-69
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• 1988

Analyzing short-term records of sea level data, we show that the amplitudes of diurnal tides along the southern coast of Jeju-Do are significantly larger than those along its northern coast. The amplitude-phase diagrams of $K_1$ and $O_1$ look very similar to that of $M_2$ shown by Kim and Lee (1986), indicating characteristics of the scattering of long waves by Jeju-Do.

• Journal of the Speleological Society of Korea
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• no.84
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• pp.43-45
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• 2008

Jeju Island is formed by lava flow streams with the Mt. Halla in the center. The Mt. Halla‘s crater or other parasitic volcano produced lava flows creating lava plateau in this area. There are one thousand volcano caves in the world, and 50% of them are located in the west coast of United States. There are 186 volcano caves in Italy, 100 in Mt. Fuji, Japan, and 70 in Jeju Island. Jeju Island‘s east-west axis four sides are world-renown volcano zones with basalt strata that feature low viscosity and fluidity.