• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.45 no.3
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• pp.157-164
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• 2009

Due to change of various marine environments according to seawater temperature rising, Japanese common squid(Todarodes pacificus), which was distributed in East Sea, was recently caught in Yellow Sea during a summer season from 2006. The fishery resources density research was carried out in Korea-China Provisional Water Zone using trawl fishing gear and acoustics in National Fisheries Research & Development Institute in Korea. This paper showed the analysis on the acoustical backscattering strength by two frequencies(38kHz, 120kHz) for Japanese common squid by acoustical scattering theoretical model based on size distribution for survey period, and estimate the density distribution for squid s integrated layer which was extracted from any scatterers distributed in water column using two frequency difference method which has been used to distinguish fish shoals or specific target scatterers from sound scattering layer which is composed of various zooplankton. Furthermore, the entire range of their density estimation was suggested using by Monte Carlo simulation under considering each uncertainty such as size distributions or swimming angle and so on in survey area.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.3
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• pp.290-296
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• 2009

Acoustic technologies are commonly used to estimate biomass and distribution of fisheries resources in coastal areas and the open ocean. The pelagic species of Engraulis japonica, Scomber japonicus and Sardinops melanosticta spawn migrate to the southern part of the Sea of Korea and capture of these three species comprise 50% of the total abundance in Korean waters. Since 1970, anchovy landings have increased to 0.2 million tons in 1990, 0.27 million tons in 2001, and 0.25 million tons in 2003. Acoustic surveys were conducted on 24-26, May and 20-21, June 2005 around the Tongyeong, Geojae, and Namhae anchovy fishing ground using a dual beam echo sounder (DT-5000, 200 kHz Biosonics). Using this approach, information was obtained on the distribution (depth and position) of zooplankton, and adult and juvenile anchovy. We calculated and compared anchovy biomass using simple summation and geostatistic methods to assess the advantages and constraints of the two techniques.

• Environmental Analysis Health and Toxicology
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• v.25 no.2
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• pp.153-159
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• 2010

Perfluorooctane sulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA) are the principal chemicals known as perfluoroalkyl acids (PFAs). Despite the widespread use of these compounds, relatively little is known about their fate and effects. The purpose of this study was to determine the toxic effects of PFOS and PFOA on Daphnia magna. In the acute toxicity test, D. magna were exposed for 48 hours at concentrations of 0, 30, 45, 67.5, 101.25 and 151.88 mg/L PFOS, and 0, 100, 160, 225, 337.5 and 506.25 mg/L PFOA, respectively. In the case of chronic toxicity test, D. magna were exposed through water for 21 days at concentrations of 0, 0.375, 0.75, 1.5, 3 and 6 mg/L PFOS, and 0, 1.25, 2.5, 5, 10 and 20 mg/L PFOA, respectively. Acute toxicity was assessed on the basis of immobility, while chronic toxicity was assessed on the basis of fecundity. The acute toxicity test on PFOS and PFOA showed that the values of $EC_{50}$ were 50.90 mg/L and 253.47 mg/L, respectively. In the chronic test, fecundity was reduced significantly at 1.5 mg/L of PFOS and 10 mg/L of PFOA, respectively. These results indicated that PFOS is more toxic to zooplankton than PFOA, and both chemicals have some hazard demonstrates risk for acute or chronic toxicity to freshwater organism.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.2
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• pp.3-14
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• 2001

In order to predict nutrient circulation in Hakata bay, we have developed an ecosystem model named the Sediment-Water Ecological Model (SWEM). The model, consisting of two sub-models with hydrodynamic and biological models, simulates the circulation process of nutrient between water column and sediment, such as nutrient regeneration from sediments as well as ecological structures on the growth of phytoplankton and zooplankton. This model was applied to prevent eutrophication in Hakata bay, located in western Japan. The calculated results of the tidal currents by the hydrodynamic model showed good agreement with the observed currents. Moreover, SWEM simulated reasonably well the seasonal variations of water quality, and reproduced spatial heterogeneity of water quality in the bay, observed in the field. According to the simulation of phosphorus circulation at the head of the bay, it was predicted that the regeneration process of phosphorus across the sediment-water interface had a strong influence on the water quality of the bay.

• Animal cells and systems
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• v.13 no.1
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• pp.59-69
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• 2009

This paper documents the defining morphological characteristics of the larval stages of Chionoecetes tanneri Rathbun, 1893, the grooved Tanner crab, from specimens reared in the laboratory. Chionoecetes tanneri larval stages include two zoeae and one megalopa. The first zoea is characterized by: six setae on the posterior margin of the carapace; postero-lateral spines on abdominal somites 3 and 4, extending beyond the posterior margin of adjacent somites and bearing 9-10 spinnules; 12 plumose setae and one stout distal plumose seta present on the margin of the scaphognathite of the maxilla; and one fused lateral spine and one articulated dorso-medial spine on each fork of the telson. The second zoea is characterized by: 9 setae on the postero-lateral margin of the carapace; a serrated mandible molar; a mandibular palp bud; 25-26 plumose setae on the margin of the scaphognathite of the maxilla; pereiopods with well-developed gills and buds; and four pairs of stout setae on the posterior margin of the telson. For the megalopal stage, the distinguishing characteristics include: a rostral spine equal in length to the supraorbital spine; six setae on the exopod of the uropod; and a single spine on the ischium of the second pereiopod. This study allows C. tanneri larvae to be distinguished from the larvae of known sympatric congeners. This information provides a basic taxonomic tool for researchers in fisheries management and zooplankton ecology who are addressing issues related to trophic interactions, metapopulation dynamics and ecosystem impacts in the evolving marine resource management strategies in the North Pacific, and those related to Chionoecetes species in particular.

• Korean Journal of Ichthyology
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• v.22 no.4
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• pp.249-255
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• 2010

Ecological characteristics of landlocked and anadromous populations of Hypomesus nipponensis were investigated from December 2008 to April 2009 in the Soyangho (landlocked population) and Hyangho (anadromous population). Morphological differences between the landlocked and anadromous populations were not found. The spawning season was March in the Soyangho and late February in the Hyangho. Individuals of both populations were sexually mature at sizes over 60 mm total length. Gonadosomatic index of the landlocked population (female: 20.5%, male: 3.7%) was higher than in the anadromous population (female: 17.4%, male: 3.3%). Number of eggs in the ovaries was greater in the anadromous Hyangho (7,325) population and fewer in the Soyangho (4,902) population; this corresponded to the greater total length in the former. Condition factor was 0.6 (0.49~0.74) in the Soyangho population and 0.7 (0.47~0.76) in the Hyangho population. Stomach contents of H. nipponensis consisted mainly of zooplankton and aquatic insects, and the size of prey was larger in the Hyangho population than in the Soyangho population.

• Journal of Ecology and Environment
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• v.39 no.1
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• pp.31-42
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• 2016

The object of this study was to determine long-term temporal and spatial patterns of nutrients (nitrogen and phosphorus), suspended solids, and chlorophyll (Chl) in Chungju Reservoir, based on the dataset of 1992 - 2013, and then to develop the empirical models of nutrient-Chl for predicting the eutrophication of the reservoir. Concentrations of total nitrogen (TN) and total phosphorus (TP) were largely affected by an intensity of Asian monsoon and the longitudinal structure of riverine (Rz), transition (Tz), and lacustrine zone (Lz). This system was nitrogen-rich system and phosphorus contents in the water were relatively low, implying a P-limiting system. Regression analysis for empirical model, however, showed that Chl had a weak linear relation with TP or TN, and this was mainly associated with turbid, and nutrient-rich inflows in the system. The weak relation was associated with non-algal light attenuation coefficients (Kna), which is inversely related water residence time. Thus, values of Chl had negative functional relation (R² = 0.25, p < 0.001) with nonalgal light attenuation. Thus, the low chlorophyll at a given TP indicated a light-limiting for phytoplankton growth and total suspended solids (TSS) was highly correlated (R² = 0.94, p < 0.001) with non-algal light attenuation. The relations of Trophic State Index (TSI) indicated that phosphorus limitation was weak [TSI (Chl) - TSI (TP) < 0; TSI (SD) - TSI (Chl) > 0] and the effects of zooplankton grazing were also minor [TSI (Chl) - TSI (TP) > 0; TSI (SD) - TSI (Chl) > 0].

• Journal of Aquaculture
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• v.11 no.2
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• pp.261-269
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• 1998

The harpacticoid copepod, Tigriopus japonicus is one of the important zooplankton as a live food the production of marine fish fry. This reserch was carried out to investigate the culturing method and dietary value of T. japonicus. The reproduction of this copepod was analysed in the culturing systems (tne opened and the closed systems) and the surface area of the substate plates for the mass culture. Survival rate of the mature female and the number of nauplii produced per female for two day was higher in the open culturing system than in the close system. However, the result of survival rate of the nauplius was reversed. Larger surface area of the culturing vessel accommodated higher density of this bentic copepod. In polyculture of T. japonicus and rotifer (B. plicatilis), growth of T. japonicus seems to be dependent on the rotifer density. But rotifer seems to be independent on the copepod. With regard to dietary value, this copepod is better than Artemia nauplius for the larvae of red sea bream and tiger puffer which feed by picking. However, it is inadequate for bottom fish larvae as flounder.

• 한국해양학회지
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• v.29 no.3
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• pp.287-295
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• 1994

The relationship between temperature profile and backscattering strength(S/SUB y/) computed by the ADCP data is studied in warm eddy of the southwestern parts of the East Sea of Korea in April, 1993. The result shows that S/SUB y/ with depth in N-S direction shows a symmetric shape that is almost the same as the warm eddy. But the profile of S/SUB y/ with depth in N-S direction shows a symmetric shape that is almost the same as the warm eddy. But the profile of S/SUB y/ in E-W direction shows asymmetric shape where the S/SUB y/ of the eastern parts is smaller than that of western parts. The asymmetric distribution may be due to the migration of a large number of scatterer(mainly zooplankton) carried by EKWC(East Korea Warm Current). Profile of the S/SUB y/ is similar to the temperature with depth in the ADCP data of CREAMS 93(Circulation Research of the East Asian Marginal Seas).

• Korean Journal of Environmental Biology
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• v.34 no.4
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• pp.281-291
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• 2016

Bloom of small centric diatom Stephanodiscus is quite occasional in winter season in temperate freshwater ecosystems. It often leads to degradation of water quality and affects the quality of supplied drinking water. In a previous study, we have found that naphthoquinone (NQ) 4-6 derivate is an effective tool for efficient mitigation of natural S. hantzschii blooms. In the present research, polylactide (PLA) and agar foam were used as immobilized agent for NQ 4-6 to improve the efficiency of NQ 4-6 compound releasing process for its application under various field conditions. Mesocosm experiments at 10 ton scale suggested that the abundance of S. hantzschii was continuously increased in the control and upon treatment of the mesocosm with immobilized NQ 4-6 from PLA and agar foam. Their algicidal activities were 78.8% and 77.1%, respectively, on S. hantzschii after 10 days. In the mesocosm experiments, the dynamics of biotic (bacteria, HNFs, ciliates, zooplankton) and abiotic (water temperature, dissolved oxygen, pH, conductivity, nutrients) factors remained unaffected. They exhibited similar trends in the control and treatment groups. Therefore, the immobilized NQ 4-6 from PLA and agar foam has potential to be used as an alternative algicidal substance to effectively mitigate natural S. hantzschii blooms under various field conditions. In addition, it not only can be used to control S. hantzschii, but also is an effective technique. The immobilized NQ 4-6 showed stable controlled release in desired system.