• Article

    Mesozooplankton Community Structure in the Yellow Sea in Spring

    봄철 황해의 중형동물플랑크톤 군집 구조

    Garam Kim and Hyung-Ku Kang

    김가람, 강형구

    We investigated mesozooplankton in the Yellow Sea in spring to understand its community structure and relationship with environmental factors. Total mesozooplankton density ... + READ MORE
    We investigated mesozooplankton in the Yellow Sea in spring to understand its community structure and relationship with environmental factors. Total mesozooplankton density ranged from 1,542 to 7,367 ind. m-3 and the biomass ranged from 3 to 42 mg C m-3. The total density and biomass had a positive relationship with chlorophyll-a (chl-a) concentration. The mesozooplankton community was divided into two groups at 125.5 E by cluster analysis: one was an inshore group and the other was an offshore group. The inshore group of mesozooplankton was of high density but low diversity, while the offshore group was of high diversity but low density. Copepod Acartia hongi and its copepodites were the most abundant species, comprising 27.8% of the total mesozooplankton density. A. hongi was especially abundant at the inshore, serving as the indicator species of the inshore group. Redundancy analysis found a positive relationship between the density of A. hongi and chl-a concentration. Oithona similis and Centropages abdominalis were 2nd and 3rd dominant species comprising 9 and 7% of the total density, respectively. The density of O. similis was positively related to water depth, but C. abdominalis was related to chl-a concentration. Chl-a concentration seems to influence significantly the mesozooplankton community structure in the Yellow Sea in spring, rather than water temperature or salinity. - COLLAPSE
    December 2020
  • Article

    New Record of Oncaea prendeli (Copepod, Cyclopoida, Oncaeidae) in Korean Waters
    Kyuhee Cho, Jong Guk Kim, and Jimin Lee
    Oncaea prendeli Shmeleva, 1966 is redescribed here based on a specimen collected using a fine-mesh net in the epipelagic layer in the ... + READ MORE
    Oncaea prendeli Shmeleva, 1966 is redescribed here based on a specimen collected using a fine-mesh net in the epipelagic layer in the south sea of Jeju Island, Korea. The Korean specimen is generally similar to Mediterranean specimens in terms of morphological characteristics, but it shows a few minor differences in a slightly larger length-to-width ratio for the distal endopod segment of the antenna, a relatively shorter caudal seta IV, and additional ornamentation on the maxillule and maxilla. This species is distinguishable from the most similar congeneric species, O. tregoubovi Shmeleva, 1968, and three species of the genus Spinoncaea Böttger-Schnack, 2003 by the distal and lateral armature of the antenna, ornamentation on the female maxilliped, spine number on the endopod of leg 2, and proportional length of setae on the caudal ramus. Moreover, spine lengths on the exopods of legs 2–4 are proposed as new morphological characters for the identification of congeners. This is the first record of O. prendeli in Korean waters. - COLLAPSE
    December 2020
  • Article

    Study on Load Reduction of a Tidal Steam Turbine Using a Flapped Blade

    플랩 블레이드를 이용한 조류 터빈의 부하 저감에 대한 연구

    Dasom Jeong and Jin Hwan Ko

    정다솜, 고진환

    Blades of tidal stream turbines have to sustain many different loads during operation in the underwater environment, so securing their structural safety ... + READ MORE
    Blades of tidal stream turbines have to sustain many different loads during operation in the underwater environment, so securing their structural safety is a key issue. In this study, we focused on periodic loads due to wave orbital motion and propose a load reduction method with a blade design. The flap of an airplane wing is a well-known structure designed to increase lift, and it can also change the load distribution on the wing through deflection. For this reason, we adopted a passive flap structure for the load reduction and investigated its effectiveness by an analytical method based on the blade element moment theory. Flap torsional stiffness required for the design of the passive flap can be obtained by calculating the flap moment based on the analytic method. Comparison between a flapped and a fixed blade showed the effect of the flap on load reduction in a high amplitude wave condition. - COLLAPSE
    December 2020
  • Note

    Embryonic Development and Hatchability in the Reciprocal Hybrids of Kelp Grouper (Epinephelus bruneus) and Red-Spotted Grouper (Epinephelus akaara)
    Min Joo Kang, Choong Hwan Noh, Hee Jung Choi, Dae Won Park, and Sung-Pyo Hur
    In this study, the embryonic development and hatchability of eggs fertilized by the reciprocal hybrids of kelp grouper (Epinephelus bruneus) and red-spotted ... + READ MORE
    In this study, the embryonic development and hatchability of eggs fertilized by the reciprocal hybrids of kelp grouper (Epinephelus bruneus) and red-spotted grouper (E. akaara) were evaluated with the goal of establishing a novel hybrid with enhanced growth and viability during the farming period in the temperate waters of Korea. The fertilization rates were lower for hybrids than for maternal purebreds and were significantly higher in the red-spotted grouper ♀ × kelp grouper ♂ hybrid (RGKG, 89.61 ± 1.58%) than in the kelp grouper ♀ × red-spotted grouper ♂ hybrid (KGRG, 74.82 ± 4.23%, p < 0.05). Unlike the fertilization rates, the hatching rates of fertilized eggs were similar between hybrids and maternal purebreds and did not differ significantly between KGRG and RGKG (72.74 ± 3.60% vs. 75.23 ± 2.20%, respectively, p > 0.05). The embryonic development of the hybrids was similar to that of maternal purebreds; however, irregular cleavage and asymmetric blastoderm were noticeable in the developing eggs of KGRG hybrids. The deformity rates of newly hatched larvae were higher in hybrids than in maternal purebreds and were significantly higher in KGRG than in RGKG (17.47 ± 1.28% vs. 7.11 ± 0.54%, respectively, p < 0.05). These results demonstrate the potential to produce viable larvae from these two hybrids. Although the production efficiency of KGRG was lower than that of RGKG, the fertilization, hatching, and deformity rates make both hybrids useful for further comparative studies regarding economic aspects. - COLLAPSE
    December 2020