• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.3
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• pp.155-162
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• 2009

To characterize the initiation, propagation and termination of Cochlodinium polykrikoides blooms in the southeast coastal waters of Korea, 2008, we analyzed the data set of phytoplankton composition, physical and chemical water properties, and meterological data. C. polykrikoides bloom in 2008 were long lasting and restricted to the coastal area with a low density. Our results indicate that C. polykrikoides blooms were affected by the atypical cold waters occurring in east-south coastal water in the early July. The cold water masses probably protected the free living cells of C. polykrikoides from entering into the coastal area from offshore waters as a pelagic seed population. The low density blooms of small scale established possibly by the germination of C. polykrikoides cyst in shallow coastal bottom could have not spread over because of the weak wind and low nutrient concentrations caused by severe drought in July and September.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.1
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• pp.68-72
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• 2009

To gain a greater understanding of the potential for future harmful algal bloom (HAB) outbreaks and to trace the dispersal paths of dinoflagellates, sediment samples were collected from 13 stations in the southeastern Yellow Sea. 23 different types of dinoflagellate resting cysts were identified from the samples. Protoceratium reticulatum (1-391 cells/g dry weight), Gonyaulax scrippsae (0-254 cells/g dry weight), G. spinifera (0-301 cells/g dry weight) and Alexandrium spp. (ellipsoidal type) (0-76 cells/g dry weight) were the dominant species at all surveyed stations. The overall distribution pattern demonstrated that the resting cyst densities were highest in the offshore area and decreased gradually toward the Korean coast. On the other hand, the composition rate of resting cysts of the heterotrophic dinoflagellate species to the total dinoflagellates was higher in the Korean coast region than in the offshore area. We supposed that this distribution pattern of dinoflagellate resting cysts appeared to be influenced by the hydrographic features and environmental conditions of the Yellow Sea.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.4
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• pp.195-205
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• 2013

Excessive input of organic matters from fish cage farming has been considered as one of the major factors disturbing benthic ecosystem, especially in semi-enclosed coastal waters. Recently offshore aquaculture in the vicinity of Jeju-do has been introduced to minimize that kind of negative impact. This study was conducted to investigate the ecological impacts of offshore aquaculture on the macrobenthic polychaete communities. A total of ten sampling works were carried out for 28 months, spanning from 10 days after starting giving feed to 3 months after stopping giving feed. During the study period, mean current velocity was quite strong with the range of 50 cm/s to 70 cm/s. TOC of surface sediment was constantly low. Significant changes in polychaete community were detected just three months after starting giving feed, which were the increase of the number of species and density at all stations. Up to 18 months after the start of farming, the amount of feed provided played an important role in the fluctuation of the number of species and density, especially at 0 m and 10 m stations. After reducing the amount of feed provided, dominance of some opportunistic species within 10 m distance from fish cages still lasted to the end of aquaculture. However, opportunistic species disappeared 3 months after the end of farming, which indicated the sign of recovery from the disturbance. From these results, the amount of food input and the period of cultivation were critical factors disturbing polychaete community and ensuing changes in this offshore and oligotrophic waters as well. In addition, study on the changes of polychaete community structure before and after fish farming showed more detailed changes in benthic ecological state than geochemical approach did.

• Journal of Drive and Control
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• v.14 no.3
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• pp.18-24
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• 2017

The purpose of this paper is to develop a new submersible fish cage operated by a pneumatic system for offshore aquaculture. Although some researchers have investigated modeling and control of fish cages, such cages consist of variable ballast tanks that with closed cylinders and thus present a maintenance issue. In solving the issue the new submersible fish cage investigated consists of bottom-opening cylinders. Accordingly, we designed a mathematical model of the concept and applied Sliding Mode Control for nonlinear angle control. Some experiments conducted under assumed conditions indicate that the angle of the system converges to zero under all conditions and the control has the stability to balance the fish cage.

• Journal of Life Science
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• v.19 no.12
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• pp.1851-1854
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• 2009

This study correlated changes in the plasma levels of estradiol-$17{\beta}$ (E2) with changes in the gonadosomatic index (GSI) and ovarian development during the annual reproductive cycle of the pike eel Muraenesox cinereus, collected at the Tongyung coast region. Ovarian maturity was classified based on histological observations; the perinucleolus stage (November to February), the oil droplet stage (March to April), the early vitellogenic stage (April to May) and the late vitellogenic stage (June to October). Seasonal changes in the GSI were correlated with water temperature and reflected the degree of ovarian maturity. Plasma E2 levels were correlated with changes in the GSI, which increased from April to a peak in July, and the levels remained comparatively high until October. These data indicated that changes in the GSI and plasma E2 levels are correlated with the annual ovarian activity of the pike eel. In this study, however, female pike eels were not collected during the spawning stage. Therefore, spawning of this species seemed to be closely related to its migration toward the deep sea of offshore.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.4
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• pp.266-271
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• 1991

Probably herbivorous fishes were visibility main body as aquatic substantial production in offshore and adjacent sea. It is a major problem to estimation of energy conversion rate by hervivores from primary production when to be measurement for potential productivity of herbivores as above meaning according to deductive method. This was deal with review of I index, with mean transfer efficiency from food in seawater to food in gut be eaten by a particular species. Yet $K_i$ was not settled with an established theory. In this review coefficients of food selection or electivity indices suggested by two Russian biologists, Ivlev and Sorygin, (r-p) /(r+p) and (r/p) were understand unsuitable to use with the transfer efficiency $K_i$. But CCOS that is one of community resemblance chord is suggested to be possible with someone a treatment, as (CCOS)$\times$(Filtering rate).

• ALGAE
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• v.17 no.1
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• pp.11-19
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• 2002

Twenty-nine culture strains belonging to the genus Alexandrium Halim (Dinophyceae) were established from water column or sediments in Korea. Seventeen isolates were identified as A. tamarense (Lebour) Balech, eight isolates as A. sp. cf. catenella and one as A. catenella (Whedon et Kofoid) Balech according to the presence or absence of a ventral pore, the shape of the posterior sulcal plate and the sulcal width. Three isolates were unable to be identified due to considerable distortion of thecal plates and lack of enough materials, but typical of A. tamarense and/or A. catenella. The overall cell shape of A. tamarense was usually longer than wide. The posterior sulcal plate was definitely longer than wide dorsoventrally, and sulcus extended posteriorly without apparent widening. They were distributed in three major coasts of Korea. In contrast, the cell shape of A. sp.cf. catenella was generally anterior-posteriorly flattened. The transversal axis of the posterior sulcal plate was always longer than the longitudinal, or both axes were nearly equal in length. Its sulcus was broader than that of A. tamarense and widened in the direction of antapex about 1.5 times. This morphotype existed in nearshore and offshore waters of the southern Korea sea. One of A. catenella isolates from Jinhae Bay showed no conspicuous differences with A. sp. cf. catenella except for the consistent absence of a ventral pore.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.2
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• pp.83-93
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• 2020

In fisheries, the importance of designing efficient fish cages is being emphasized as aquaculture has become more production than capture fishing. Particularly, the gravity cage system is one of the popular fish cage system in Korea. Currently, gravity cages of various shapes and sizes are being widely designed and installed in offshore and inland seas. The cage is subject to external forces, such as currents and waves, and the shape of the structure and tension on the ropes changes according to these external forces. Thus, it is important to accurately calculate these dynamic behavior, including the external forces and tension on the structure during the design stage. In this study, three types of cage systems with an equal internal volume of 8000 ㎥ were analyzed using mass-spring models and their behavior was interpreted through simulations. These simulations were used to analyze the behavior and tension of the ropes in response to currents and waves to aid in the selection of individual cage sizes for a given total volume. The numerical calculation results indicate that depending on the flow rate, the most resistant system is System 1, which has eight strays, and System 2 and System 3 have 69.4% and 54.8% of the resistance of System 1. Further, total resistance increased as the number of cages increased for all flow rates.

• Journal of the Korean Association of Geographic Information Studies
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• v.10 no.2
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• pp.47-57
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• 2007

Real-time oceanographic information system was developed using platforms of aquaculture farms to examine causes of mass mortality of hatchery fishes, and to reduce the damage of mass mortality which has been occurred frequently off coast by abnormal change of ocean conditions. The system had the advantages of direct data distribution to fishermen at the farm and instant maintenance of equipments due to easy access to the farms and residents at the farms in comparison with offshore mooring buoy system. To avoid discontinued measurement of the system, repairs caused by malfunction of equipments, bimonthly preventive maintenances and daily monitoring of measured data were systematized. Confidence intervals calculated by a statistical method using accumulated data were applied to data management. Such activities could minimize discontinuance of measurement and keep information more trustful. In addition, the system has various ways of data distribution. Through homepage and e-mail in the internet, information was provided to public. Display units which were connected to equipments at the farm gave the measured data directly to fishermen, which guided them to run their farm scientifically. Finally large display unit was installed at a fish market and showed the measured data at the nearest station with tide and weather information. Proper region for aquaculture and wintering region were studied using temperature data obtained by the system in 2006. The system will contribute to reduce economic damage of coastal fishery and to understand coastal marine environment.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.4
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• pp.325-332
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• 2008

To characterize the initiation, propagation and termination of Cochlodinium polykrikoides blooms in the southeast coastal waters of Korea, 2007, we have analyzed the data set of phytoplankton composition, physical and chemical water properties, and meterological data. The development of C. polykrikoides bloom in 2007 can be summarized in three steps. The first stage from middle of July to end of August was characterized by an unusually persistent and strong southerly wind. C. polykrikoides blooms established already by the strong wind in the middle of south coastal waters were advected intermittently into the study area. Accordingly, highly variable cell densities of C. polykrikoides were observed. At the second stage a favorable growing conditions for C. polykrikoides was developed, which was directed by changes in wind direction from south to northeast and thus enhanced transportation of offshore waters into inshore (August 8 to 30). C. polykrikoides bloom occurred through typical mechanism and showed high cell density. The last stage was represented by disappearance of C. polykrikoides. Typoon 'Nari' carrying heavy rain brought an unfavorable habitat to C. polykrikoides. Low saline condition formed in coastal water due to typoon effects continuously drove the dominant species to diatoms and flagellates which were prevailing over C. polykrikoides in this circumstances(from the middle of September). These stepwise processes could be the causative mechanism of the extraordinarily persistent C. polykrikoides bloom observed in southeast coastal water of Korea, 2007.