• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.59 no.4
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• pp.315-327
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• 2023

In the last five decades, there has been a consistent decline in the total catch of fisheries in the Korean jurisdiction since the peak in 1986. The decline in catch slowed and slightly rebounded in the 2000s, but changed back to a decline in the 2010s. As indicators that can identify changes in the marine ecosystem, trophic level (TL), biodiversity index (H'), and the ratio between pelagic fish and demersal fish (P/D) were analyzed by each local marine ecosystem. There were some different changes in each local marine ecosystem, but the mean TL and H' decreased and P/D increased in general in Korean waters. Demersal fish, which were dominant in the 1970s and 1980s, declined, and small pelagic fish and cephalopods have dominantly changed since the 1990s. However, these changes are not simple, and they are fluctuating in complex ways relating to each marine ecosystem and the timing. It is believed that changes in marine ecosystems in Korean waters are likely caused by a combination of fisheries and climate change. The ecosystem indicators reflected a change in the total catch, a sharp drop in catch of demersal fish, and increasing catch of pelagic fish since the mid-1980s.

• Journal of Korean Society on Water Environment
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• v.23 no.5
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• pp.676-682
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• 2007

The bacterial number, extracellular enzyme activities and structure of bacterial community which are major constituent of aquatic ecosystem within the artificial vegetation island (AVI) were compared to those of the nearby pelagic lake waters in order to evaluate the possibility of the AVI as a eco-technological measure for water quality improvement and restoration of littoral zone in man-made reservoirs. There was not a significant difference in the total number of bacteria, but the number of active (viable) bacteria within the AVI was about 0.7 to 4.1 times higher than nearby pelagic lake water. The ratio of the number of active bacteria versus the total number of bacteria was also higher in the AVI than nearby pelagic lake water. The activities of ${\beta}$-glucosidase and phosphatase were 1.0 to 13.1 and 0.8 to 7.3 times higher respectively in the AVI than nearby pelagic lake water, showing that microorganisms were more active within the AVI. The bacterial communities of the two waters, examined by FISH method, did not indicate a clear difference in the springtime when the growth of macrophytes was immature, but during summer and fall it showed a clear difference indicating the formation of distinct bacterial community within the AVI compared to nearby lake water. From the results of this study, we conclude that AVI can contribute to make up the littoral ecosystem which show rapid cycling of matters through active detritus food chain in the dam reservoirs which have unstable aquatic ecosystem due to short hydraulic residence time and to strengthen the self-purification capacity of the lake.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.193-198
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• 2012

Long term changes in winter time(JFM) sea surface temperature(SST) and marine ecosystem of different Korean waters during last five to six decades were illustrated. Fishing intensity with climate-ocean variability(e.g. SST) have been increasing since 1970s in all of the Korean marine waters. Winter SST around Korean waters went to colder regime in early 1980s and after the late 1980s increased gradually. After 1988/89 CRS all of the waterbody started warmer regime and well coincided with the CRS phenomena. Large predatory, small pelagic and crustacean and mollusks abundance were well coincided by the warmer SST regime after 1988/89 CRS and changed the fishery from demersal fishery to pelagic fishery. Ecosystem parameter of Mean Trophic Level(MTL) showed continuous decreasing trend since mid of 1970s which was mostly affected by the increasing of lower trophic level species. Fishing in balance(FIB) index showed increasing pattern since early 1970s to the late of 1970s and from early 1980s it was almost stable until now. Finally wasp-waist population of anchovy and Japanese sardine have a greater impact to the whole MTL since early 1970s.

• Journal of Ocean Engineering and Technology
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• v.21 no.2 s.75
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• pp.42-49
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• 2007

It has been known that shallow-water regions, such as tidal flats, sea grass and sea weed beds have water purification capability, and they also serve as nursery grounds for many fishes. On the other hand, tidal flat areas are economically attractive sites for reclamation, to be used for developing industries. When developing shallow-water areas, we have to propose a plan to mitigate the environmental impact associated with such a development plan. However, it is difficult to estimate the affects on the ecosystem and water purification, and the literature related to this matter is insufficient. In order to evaluate the ability of coastal tidal flat and to predict the future changes, it is necessary to develop a reliable prediction technique and construction of data by using a field investigation. In this study, we carried out a numerical model test for the tidal flat ecosystem, using the pelagic system and the benthic system, simultaneously, in order to show a change in the tidal flat ecosystem. The flow of nitrogen, phosphorus and carbon has been identified as a primary consideration of marine ecosystem components, and the capability of water purification and the change of the tidal flat were predicted using this flow. In order to make a more reliable prediction, a field investigation to determine tide, current and creatures of the object coastal area has been done. The purification capability of this shallow-water region is estimated from the model results. According to the results of experiments, the tidal flat has a capability of water purification (Sink) of 11mgN/m2/day, but the other area has a load (Source) of 20mgN/m2/day. As a result, we could confirm that the tidal flat of an object coastal area plays an important role in water purification.

• Ocean Science Journal
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• v.42 no.3
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• pp.179-192
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• 2007

Understanding in climate effects on marine ecosystem is essential to utilize, predict, and conserve marine living resources in the 21st century. In this review paper, we summarized the past history and current status of Korean fisheries as well as the changes in climate and oceanographic phenomena since the 1960s. Ocean ecosystems in Korean waters can be divided into three, based on the marine commercial fish catches; the demersal ecosystem in the Yellow Sea and the East China Sea, the pelagic ecosystem in the Tsushima Warm Current from the East China Sea to the East/Japan Sea, and the demersal ecosystem in the northern part of the East/Japan Sea. Through the interdisciplinary retrospective analysis using available fisheries, oceanographic, and meteorological information in three important fish communities, the trend patterns in major commercial catches and the relationship between climate/environmental variability and responses of fish populations were identified. Much evidence revealed that marine ecosystems, including the fish community in Korean waters, has been seriously affected by oceanographic changes, and each species has responded differently. In general, species diversity is lessening, and mean trophic level of each ecosystem has decreased during the last $3\sim4$ decades. Future changes in fisheries due to global warming are also considered for major fisheries and aquaculture in Korean waters.

• Animal Systematics, Evolution and Diversity
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• v.36 no.3
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• pp.236-239
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• 2020

Pelagic tunicate, Thetys vagina Tilesius, 1802, is newly reported from Korean waters. The genus Thetys Tilesius, 1802 is also first recorded as Korean fauna. Thetys vagina is the only valid species in the genus Thetys. It is distinct from other genera by having at least 16 body muscles widely interrupted, no anterior proboscis, bent alimentary canal in the solitary oozooid, and five narrow body muscles, no ventral peduncle, an almost compact loop alimentary canal in the aggregate blastozooids. The specimens of T. vagina examined in this study were collected at the subtidal zone of Ulleung-do Island by scuba diving. In this paper, the detailed descriptions and photographs of both the solitary and aggregate living forms of T. vagina are provided.

• Ocean and Polar Research
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• v.30 no.3
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• pp.303-312
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• 2008

Despite the impacts of the climate changes on the pelagic ecosystem, few studies have examined the pelagic-benthic coupling in the adjacent East China Sea and Korea Strait. Therefore, the species composition and abundance of the macrobenthic community, as well as the potential food sources of benthic fauna were investigated in the present study using stable isotope analysis (${\delta}^{13}C\;and\;{\delta}^{15}N$) for suspended particulate organic matter (SPOM), sedimentary organic matter (SOM), phytoplankton, and zooplankton. A total of 157 macrobenthic fauna were collected, and the density of the macrobenthic fauna ranged from 4 to 434 ind./0.25 $m^2$, with an average density of 149 ind./0.25 $m^2$. The density of the benthic fauna increased moving from offshore shelf sites to coastal sites adjacent to the Korea Strait. Cluster analysis showed that the macrobenthic communities consisted of three distinct groups: group A in the Korea Strait, group B in the East China Sea, and group C near Ieodo. The dominant species in group A were the amphipods Photis japonica and Ampelisca miharaensis, followed by the polychaete Scolotoma longifolia. Environmental variables, such as the temperature of the seawater and sediment, and oxygen, and chlorophyll a levels, appeared to affect the structure of the community, suggesting the importance of coupling with the pelagic system. The ${\delta}^{13}C$ values of SPOM and zooplankton ranged from -22.97 to -23.5% and -19.92 to -21.86%, respectively, showing a relatively narrow range(<1%) between the two components. The difference between the ${\delta}^{13}C$ values of SOM and pelagic organic matter was also within 1%, suggesting that the SOM originated from the pelagic system, which is an important factor controlling the macrobenthic community.

• Ocean and Polar Research
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• v.41 no.4
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• pp.251-263
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• 2019

We investigated the mesozooplankton community structure during autumn in the southern Yellow Sea. Mesozooplankton density generally ranged from 352 to 2,954 ind. m^-3 and varied according to different sampling stations. The copepod Paracalanus parvus s.l. and its copepodites dominated in the communities, corresponding to 57.3% in density of the total. Surface and water-column averaged salinity were positively correlated with density of total mesozooplankton, copepods and a few dominant species, and the tunicate Thalia rhomboides was negatively related to chlorophyll-a concentration. The mesozooplankton community of the study area was divided into three groups according to the cluster analysis using species composition and density: one in the northern coastal region, another in the northern offshore region, and the other in the south. The most significant indicator species for each of the groups were Labidocera euchaeta in the northern coastal region, T. rhomboides in the northern offshore region, and Themisto sp. juveniles in the south. This study provides recent data on the characteristics of the mesozooplankton community in the southern Yellow Sea, which may be valuable for gaining a better understanding of changes in the pelagic ecosystem of the Yellow Sea.

• Journal of the korean society of oceanography
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• v.36 no.4
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• pp.109-123
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• 2001

The importance of phytoplankton, benthic vegetation, vascular marsh plants (primarly Phragmites communis and Salix gracilstyla) and riverine particulates inputs to the coastal bay food web was studied in Kwangyang Bay, Korea using stable carbon isotope ratios. Vascular marsh plants (${\delta}^{13}$C=-27.4${\pm}$0.8%o) and riverine particulates (-26.0${\pm}$0.8%o) were isotopically distinct from phytoplankton (-20.7${\pm}$0.8%o), microphytobenthos (-14.2${\pm}$0.6%o) and seagrass (8.8%o). The ${\delta}^{13}$C values of consumers in the study site ranged from -20.2 to -11.3olo suggesting the assimilation of carbon derived from both phytoplankton and benthic vegetation (including algae and seagrass), The relative importance of both pelagic and benthic origins of food sources was likely to vary depending on feeding habit of the consumers. The isotopic difference between pelagic and benthic consumers indicated that plankton-derived carbon was used mostly by pelagic consumers, but the carbon derived from intertidal benthic vegetation was incorporated into food webs through benthic consumers. The ${\delta}^{13}$C values of consumers in the present study differed noticeably from published values of the phytoplankton-based ecosystem, particularly in the $^{13}$C enrichment of benthic grazers, deposit-feeders and demersal feeders of fishes. This tendency of the $^{13}$C enrichment was also found in suspension-feeding bivalves. Taking the biomasses of benthic vegetation into consideration, benthic microalgae was likely to account for the consumer $^{13}$C enrichment. Role of terrestrially derived riverine carbon was limited to the riverine system and was not evident within the bay systems. Phragmites, despite their important biomass, appeared to be of little importance as consumer diet.

• Korean Journal of Environmental Biology
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• v.33 no.2
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• pp.240-247
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• 2015

This study was carried out to provide the preliminary data for study of zooplankton community structures and coastal pelagic ecosystem by understanding the seasonal change of zooplankton community depending on environmental factors at Dangdong bay in Tongyeong city. In this study, the environmental factors and the change of zooplankton community were analyzed for 2008 to 2011. In the results, a total of 80 species of zooplankton was sampled with a mean density of $1,599inds.m^{-3}$. The dominant species changed seasonally, and the most dominant species was Acartia steueri in winter and spring, Penilia avirostris in summer, and Evadne nordmanni in autumn. The Canonical Correspondence Analysis was conducted between the major dominant species and environmental factors. And for the environmental factors that effect the zooplankton community, the high correlation was observed with the water temperature, COD, DO and T-N, though there was slight difference among species. Therefore, more various research and environmental study are necessary to understand of planktonic ecosystem because the zooplankton community is affected by the interaction of both physical and biological factors.