• 한국해양학회지
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• v.19 no.2
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• pp.217-227
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• 1984

Fish samples were collected by a trap net during 1981∼82 at the mouth of Cheonsu Bay to determine seasonal fluctuations in abundance and species composition. Examination of a series of trap net catches indicated that trap net data could be used, at least, for a qualitative analyses of a fish community and for a quantitative study of some pelagic fishes of Cheonsu Bay. Of the 64 species collected, a few temporal components predominated in abundance because of great seasonal fluctuations of water temperature. The early spring catch showed a low abundance value, and two cold weather seasonals, juvenile Enedrias fangi and Ammodytes personatus predominated in number and in weight. The number of species, abundance value in number and in biomass showed a peak in late spring when fishes move into bay for spawning and feeding after over-winterinig in the sea. Three pelagic species or warm weather seasonals, Harengula zunasi , Ammodytes personatus and Konosirus punctatus, predominated in abundance values. In this period night catch was significantly larger than day catch in terms of number of species, abundance in number and in weight Summer data showed a marked reduction of the number of species and abundance due to the loss of spawners probably by mortality or wide dipersion after spawning. A slight increase in abundance was observed in autumn by recruitment of the young-of-the-years. This catch was predominated by three juvenile fishes, H. zunasi, E. japonica and K. punctatus, which were the same species as in spring. The autumn catch showed no significant difference between day and night compositions.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.4
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• pp.519-534
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• 2019

When the fresh water from the artificial lakes (Ganwolho and Bunamho) were discharged to Cheonsu Bay in summer to prevent the flood over the reclaimed farmland near the lakes, the impact on water qualities (nutrients, organic matters, trace metals) within the bay was investigated through four surveys (June, July, August and October, 2011). Dissolved inorganic nitrogen (DIN) increased about as much as 3-4 times over the whole water column when the freshwater was discharged. And the main species composition of DIN changed from ammonia to nitrate. Dissolved inorganic phosphorus (DIP) decreased as much as 2 times in surface waters, but increased as much as 1.5 times in deep waters, and also silicate concentrations increased as much as 3-4 times in deep waters of the inner bay. The N/P ratios in Chunsu bay seawaters were much higher (2 to 7 times) than the Redfield ratio when the freshwaters were discharged, which indicated the phosphorus limiting in the phytoplankton growth. Dissolved organic carbon (DOC) and nitrogen (DON) increased as much as about 2 times. In addition, particulate organic matters (POC, PON, POP, Bio-Si) increased as much as above 2 times in the surface waters of the inner bay. Trace metals (Fe, Mn, Co, Ni, Cu) increased in the surface waters of the inner bay, but dissolved Cd concentrations decreased as much as 2 times. Therefore, when the contaminated fresh waters from the artificial lakes were discharged into the bay, nutrients, organic matters and trace metals generally increased compared to normal period. Since the phytoplankton bloom occurred in the surface waters of the inner bay, dissolved oxygens at the surface waters were oversaturated and hence hypoxic in the deep waters. Highly enriched nutrients concentrations were found in deep waters of the inner bay, which was accompanied with the hypoxic condition. Finally, the water quality in the inner bay of the Chunsu bay was deteriorated from less than grade 3 in normal periods to grade 5 when the freshwaters from the artificial lakes were discharged in summer.

• Journal of Wetlands Research
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• v.7 no.2
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• pp.53-67
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• 2005

Cheonsu bay, which is typically a semi-closed type, is characterized by various environments such as channels, sand bars, small islands and tidal flats. The construction of Seosan A and B sea dikes from 1983 to 1985 might continuously change sedimentary environments in the northern part of the bay. In order to investigate sedimentary environment, surface and core sediments were sampled at the Hwangdo tidal flat and adjacent sea in June and October 2003. The surface sediments consisted of five sedimentary facies. Generally, the surface sediments in October were changed coarser on the tidal flat and little changed in the subtidal area compared to those in June 2003. Sedimentary facies analysis of three core sediments suggested that wave and tidal current were relatively strong in the tidal flat near Hwangdo, whereas the energy was relatively low in the tidal flat near channel. Sediment accumulation rates in the Hwangdo tidal flat during 11 months indicated that sediments deposited in the central part, whereas eroded in eastern and western sides of the tidal flat. These caused that sea dike changed tidal current patterns and sediment supplies.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.2
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• pp.171-182
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• 2022

The habitat degradation caused by large-scale reclamation leads to devastating impacts, such as fine sediment and mud shrimp Upogebia major settlement on Manila clam Ruditapes philippinarum aquaculture in the eastern Cheonsu Bay tidal flats, Republic of Korea. Despite these impacts, there is a lack of studies on the influence of fine sediments on tidal flats that constitute key mud shrimp habitats. This study provides information on the seawater-sediment environment and the influence of dissolved inorganic nitrogen (DIN) fluctuations depending on mud shrimp burrow hole density. Additionally, it discusses countermeasures for Manila clam habitat management. The results show that mean DIN effluxes in areas with a high-density of burrow holes were up to 4 times (0.12 mmol m^-2 d^-1) higher than those in sites of low-density (0.03 mmol m^-2 d^-1) within the Saho and Songhak-ri tidal flats. To manage interference within the competition zone of Songhak-ri tidal flat, it is important to utilize the settlements of spawning season in all three dimensions. Consequently, additional studies in other tidal flats are essential and research in zones where mud shrimps and juvenile clams coexist will help to determine the priorities in the efficient management of clam aquaculture.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.1
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• pp.32-42
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• 2002

The late Quaternary deposit of Cheonsu Bay, up to 20 m in thickness above the Jurassic granite basement, consists of two sedimentary units: an upper Holocene mud and sandy mud deposit (Unit M1), and a lower late Pleistocene sand and mud deposit (Unit M2; 'Kanweoldo Deposit&apos). Unit M1 is a typical Holocene tidal-flat deposit of Cheonsu Bay, showing a coarsening upward, retrogradational facies trend. This retrograding facies trend is probably due to a relative low sedimentation rate during Holocene transgression. Overlain unconformably by Unit M1, Unit M2 deposit reaches up to 14 m in thickness and is mainly composed of muddy sediment with yellow to gray color. This unit is characterized by a variety of tide-influenced signatures such as rhythmic bedding, flaser bedding, crab burrow fossil, marine dinoflagellate assemblage and authigenic glauconite mineral, indicating very similar depositional environment to those of Unit M1 deposit. It suggests that Unit M2 was probably accumulated under the tidal-flat environment during a pre-Holocene sea-level highstand. In particular, the uppermost 3-4 m of Unit M2 appears to have undergone subaerial exposure and subsequent weathering during the sea-level lowstand after deposition. Therefore, stratigraphic unconformity between Holocene and late Pleistocene sediments is highlighted by the desiccated and weathered surface of Unit M2.

• Korean Journal of Ichthyology
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• v.5 no.2
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• pp.184-193
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• 1993

The distribution, and length and age compositions of Johnius belengeri were studied using samples collected by an otter trawl from the five different coastal waters of Korea ; Asan Bay, Cheonsu Bay, waters off Yeongkwang and Samchonpo, and Yeongil Bay. This fish showed a high density of 1,147 individuals/$10,000m^2$ and predominated in abundance of the demersal fish in the coastal water off Yeongkwang. The mean density was 94 individuals/$10,000m^2$ in Cheonsu Bay and 8-24 individuals/$10,000m^2$ in Asan Bay and in the water off Samchonpo. Few fish were collected from Yeongil Bay. J. belengeri occurred from spring to autumn in the study area and showed a relatively high density in spring or in summer. The fish collected in spring and in summer composed of adults of age group I, II and III. Some juveniles began to occurred in the waters off Yeongkwang and Samchonpo from summer. The fish collected in autumn consisted mainly of the fish of age group 0. It implies that the adults after spawning moved out from the embayments for feeding. but the young fish stayed and grew in the embayments until late autumn when they migrated to the offshore water for wintering.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.4
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• pp.272-286
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• 2014

This study was performed to investigate the community structure and health assessment of macrobenthic assemblages in Cheonsu Bay, West Coast of Korea. Total species number was 224 and mean density was $1,940ind./m^2$, both of which were dominated by polychaete worms (111 species and $1,213ind./m^2$). In terms of density, the major dominant species were the bivalve Theora fragilis ($280{\pm}213ind./m^2$), the polychaetes Heteromastus filiformis ($254{\pm}218ind./m^2$), Lumbrineris longifolia ($216{\pm}41ind./m^2$), Mediomastus californiensis ($158{\pm}97ind./m^2$) and the amphipod Eriopisella sechellensis ($167{\pm}100ind./m^2$). As a result of community statistics (cluster analysis and nMDS ordination), the macrobenthic community structure was classified two major groups (inner and mouth of bay) and two stations (station 2 near Ganwol dyke in spring and summer). The Benthic Pollution Index (BPI) and AZTI's Marine Biotic Index (AMBI) were applied to assess the benthic ecological status. During the sampling periods, the BPI Index values varied between 11 (bad status) and 92 (high status). On the other hand, the AMBI Index values was ranged between 1.34 (good status) and 4.39 (poor status). In conclusion, in terms of the mean BPI and AMBI Index values, the ecological status of Cheonsu Bay were moderate status (ecotone stage) and good status, respectively.

• Ocean and Polar Research
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• v.43 no.4
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• pp.365-370
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• 2021

Manila clam Ruditapes philippinarum is present at high rates of density in tidal flats in Cheonsu Bay on the west coast of Korea, where clams often exhibit mass mortalities in late summer. We monitored the pathologic condition of clams at Hwangdo tidal flat (HD) to understand the parasitic impacts on clam fitness. Manila clams were fully ripe in July and spawned during August and September, as the histology indicated. The histology revealed that clams in HD tidal flats were heavily infected by the protozoa parasite Perkinsus olseni, as the monthly prevalence ranged from 53% (September) to 93% (August). In addition, Manila clams were co-infected by the metazoan parasite Cercaria tapetis and Parvatrema duboisi with the prevalence of 0-33% and 0-14%, respectively. Massive hemocyte infiltration and subsequent inflammation were commonly observed from the gills of P. olseni infected clams. Clusters of P. olseni trophozoites and heavy hemocyte infiltration were also observed from the female gonad, suggesting that P. olseni interferes with host gonad maturation. The larval trematode occupied almost the entire host gonad, resulting in gonad castration. In addition, Metacercaria of P. duboisi were observed from the subsurface of the mantle. Ray's fluid thioglycollate medium assay (RFTM) indicated that clams collected in August and September contained approximately 4.0×106 P. olseni cells/g gills. Condition Index (CI) declined gradually from spring to early summer, and the decline in CI was interpreted as a consequence of the heavy parasitism, as the parasites drain the host's net energy to be used in somatic growth and gamete production.

• Ocean and Polar Research
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• v.42 no.2
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• pp.141-155
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• 2020

Species composition of fish in the shallow water at Daecheon beach was determined using monthly beach seine samples collected from April 2010 to March 2011. These data were compared with the previous data, one just after reclamation in 1984-1985, and the other in 1995-96, in order to assess the post-reclamation impact of the environmental change on the fish assemblage. A total of 30 species from 1,464 individuals with biomass of 17,808 g were identified. Dominant species in the number of individuals were Chelon haematocheilus (49.3%), Takifugu niphobles (13.7%) and Paralichthys olivaceus (10.0%). Among pelagic fish, migrant juvenile fish such as Sardinella zunasi and Thryssa kammalensis were abundantly collected in 1984-85, but the catch amount was gradually decreased as time untill only few pelagic fish were collected in 2010-2011. The benthic fish were most abundant in 1984-1985 among habitat groups, and Favonigobius gymnauchen and Kareius bicoloratus were the top two predominants. Species composition of benthic fish did not exhibited drastic changes in 1995-1996, but both the abundance decline and the species composition change was evident in 2010-2011. Among the semi-benthic fish from 1984-1985 samples, Sillago japonica and Konosirus punctatus predominated. Species composition was slightly changed in 1995-1996, but significant changes were met in 2010-2011 with the two predominats, Chelon haematocheilus and Takifufu niphobles. These changes in fish species composition may reflect the post-reclamation effect of the impaired water quality and the accumulation of organic rich fine sediments.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.3
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• pp.432-442
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• 2020

Diagnostic monitoring in Korean rockfish cages was performed to survey the prevalence of pathogens in cultured Korean rockfish Sebastes schlegeli from May 2013 to July 2016. A total of 1,945 fish samples collected from the western (Cheonsu Bay and Heuksando), southern (Tongyeong and Namhae), and eastern coasts (Pohang) of Korea were tested for parasites, viruses, and bacteria. In this study, 1,264 and 334 fishes were infected with Microcotyle sebastis and Clavinema mariae, respectively. The prevalence rates of C. clavinema in fishes from Cheonsu Bay, Heuksando, and Tongyeong were 35.3%, 3.9% and 1.9%, respectively. No C. clavinema infection was detected in cultured rockfish from Namhae and Pohang. Furthermore, bacteria including Photobacterium damselae (8.9%), Photobacterium piscicola (2.3%), Photobacterium spp. (8.9%), Aeromonas salmonicida (1.8%), Aeromonas spp. (0.9%), Vibrio scophthalmi (1.5%), Vibrio spp. (3.3%), Streptococcus iniae (1.2%), and others (8.0%) were detected in 373 of 1,364 fishes. No virus was detected in any fish investigated in this study.