In order to investigate the density effect on growth performance and cultural production in tidal flat rack oyster farm, in November 2012, oysters were kept in PE bag (0.5 × 1.0 m, mesh size10 mm) at four densities: 25, 50, 75 and 100 ea/bag. The density effect on growth was only observed after the outbreak of summer mortality, which resulted in significant decrease in the growth of high density group. To minimize the effect of summer mortality, the second experiment was carried out in March 2013 at five densities: 25, 50, 75, 100 and 200 ea/bag. Being no significant mortality, significant suppression of growth in shell length and total weight but not in fatness and meat weight at 200 ea/bag. In any case, if being stocked by oysters in 40-50 mm shell length, a commercial size oyster can harvest with 6-8 months but not at 200 ea/bag. Being achieved 7.23 kg/bag at 200 ea/bag, regression analysis suggested that the optimal density was 150 ea/bag for maximum biomass production. This finding suggested a strategic approach for stocking densities: 100 ea/bag for maximum individual growth and 150 ea/bag for maximum biomass production.
This is the first report on the introduced foreign species Mercenaria mercenaria in Korea after being changed to a newly given Korean name (scientific name). Imports of this cultured species from China are increased rapidly for food in Korean market. In this study, for the purpose of the managing genetic resources we used CO1 and 16s rRNA universal primer for genetic classification of this species and conducted the phylogenetic analysis on the nineteen species similarly related species with M. mercenaria. The similarities with M. stimpsoni which belongs to the same genus as M. mercenaria were 90.8% (16s) and 81.7% (COI). The similarity with Meretrix petechialis was 56.6% (16s) and 75% (COI), which was relatively very low. Therefore, it is assumed that the probability of genetic disturbances with similar species is low. In the near future, M. mercernaria is expected to be used as biological resources for the mudflats on the west coast in Korea.
In this study, 30 polychaete samples were isolated from abalone shells, and genetic classification was performed using them. The DNA sequences corresponding to the polychaete 18S rDNA and 16S rDNA or mitochondrial cytochrome c oxidase I (CO1) regions were decoded, and the types were identified through BLAST search of NCBI. As a result of confirming the nucleotide sequence, genetic diversity was analyzed for 27 samples that were translated into ‘Annelida’, and 16 samples were identified as Polydora hoplura. In addition, Annelids such as Amphisamytha vanuatuensis, Amythas membranifera, Cirriformia chicoi, Cirratulus cirratus, Hediste spp., Notophyllum japonicum, Phyllodoce rosea, Syllis armillaris, and Terebella lapidaria have been identified. In the future, it is expected that various studies on several types of Annelids identified in abalone farms as well as continuous research on P. hoplura are needed.
In this study, we investigated bacteriological and toxicological safety of arkshell produced in the designated area of Kamak Bay from 2019 to 2020. And it evaluated whether it could be exported according to EU regulations. In 2019, 15 surveys were conducted on the A1 station. As a result, the plate count was detected 20 to 33,000 CFU/g and the fecal coliform and Escherichia coli were detected as < 18-230 and < 18-110 MPN/100g, respectively, and salmonella spp., paralytic and diarrhetic shellfish toxins were not detected in all samples. In addition, in order to confirm the representativeness of the survey sites, 4 sites were surveyed in 2020. As a result, paralytic shellfish toxins was detected 0.38-0.45 ug/kg which is less than the acceptable standard and significant difference between survey sites could not be confirmed similar to the results of Escherichia coli, etc.
The influences of inland pollution sources on shellfish production area of Yeoja bay were investigated. According to survey results, I-4 of inland pollution sources had high fecal contamination level and exceeded 6km of radius of influence during the survey period. Other pollutants have low flow rates, but fecal contamination levels were high and require management. And from January 2018 to June 2020, the range of Fecal coliform, geometric mean and 90th percentile for 21 seawaters were < 1.8-79.0 MPN/100mL, < 1.8-2.7 and < 1.8-9.1 MPN/100mL respectively. Also the range of Fecal coliform, E. coli and viable cell counts for 4 ark shell (Scapharca subcrenata) were < 18-490, < 18-490 MPN/100g and 30-4,500 CFU/100g respectively. As the results of the bacteriological evaluation, the sanitary state of Yeoja bay is level of designated area according to Korea criteria and conditionally approved area according to US criteria and Class A area according to EU criteria. For safe shellfish production in Yeoja bay, a semi-enclosed bay, it is necessary to expand the sewage treatment plant facilities and manage the pollutant.
Geochemical and benthic foraminiferal analyses of sediments (core and surface) were conducted in an abalone farm located at Pyeongil-do, Wando-gun, to understand the degree to which the abalone farming affect the benthic environment and ecology, and relativity to sedimentary environment. The C/S ratio of surface sediment was 8.24 in average (6.77-13.01), and abundance and species diversity of benthic foraminifera were 10,470 individual in 20 ml of sediments and average 3.4, respectively, in the surface sediment, although OM deposited by farming was about 7-19 cm in thickness. The effect of abalone farming on benthic ecology and geochemistry was not distinct. In the northwestern sea of Pyeongil-do and Cheok-do (Zone A), the sedimentation rate was very low (average, 0.23 cm/year), the C/N ratio was high (St. No. 9: 18.50) and Elphidium advenum known to inhabit in the entrance sea area of bay was dominantly distributed. In the adjacent sea area of Pyeongil-do and Cheok-do (Zone A), however, the sedimentation rate was very high (average, 1.73 cm/year), Epistominella naraensis known to inhabit in the open sea area was dominantly distributed. It is consequently thought that abalone farms of northwestern sea of Pyeongil-do and Cheok-do are influenced by the fast flow of Deugryang Bay, and abalone farms of adjacent sea area of them are influenced by the open sea. As mentioned above, these coexistence of various sedimentary environment in farm is thought to be caused by topographical characteristics with irregular coastline of Rias type.
To understand the distributions and characteristics of organic matter and heavy metal concentrations in the surface sediment of Jaran Bay, we investigated the grain size, IL (Ignition Loss), COD (Chemical oxygen demand), and heavy metals (As, Cd, Cr, Cu, Ni, Pb, Zn) in surface sediments collected at 10 stations in this bay in August 2017. The grain size analysis indicate that surface sediment in Jaran Bay are characterized by Silt contents ranged from 70.4-81.0% (75.9%) and Clay content 19.0-29.6% (24.1%). IL of surface sediment range from 7.5-13.9% (10.3%) and COD was in the range of 4.2-18.8 mgO2/g (12.4 mgO2/g). A seven-element of surface sediments (As, Cd, Cr, Cu, Ni, Pb, Zn) were calculated by TEL (Threshold effect level), PEL (Probable effects level), Igeo (Geoaccumulation index). pollution load index (PLI) and ecosystem risk index (ERI). As a result of applying the marine environment standards TEL and PEL, Cu and Zn were slightly higher than the TEL standard values. However, all heavy metals were observed below the PEL standard values. Igeo also indicated that As showed 60% concerning moderate risk(Class 2). The pollution load index (PLI) for evaluating the total pollution level of trace metals was 0.9-1.1 (1.1), almost study area showed relatively high pollution(1.0) and The ecosystem risk index (ERI), was 63.7-81.8 (73.8), which was a low risk to all study area. The correlation matrix displays the existence of remarkable levels of correlation with both positive and negative values among different variable pairs. IL and COD showed no correlation. However, Pb and Zn values indicated strong positive values.
To evaluate bacteriological and toxicological safety, the hygienic indicator bacteria and paralytic shellfish toxins in the shellfish produced in the Jaranman·Saryangdo area from 2016 to 2018 were investigated. The bacteriological quality of oysters collected from Jaranman·Saryangdo area meets the standard value based on shellfish hygiene of the Food Sanitation Act of Korea and the Grade A according to the classification of shellfish harvesting areas of European Union, respectively. Paralytic shellfish toxins in mussel samples collected from March to April in 2018 were detected as the range of 0.82-15.26 mg/kg, which was significantly exceeding the standard value. Paralytic shellfish toxins in oyster samples collected from the middle of April in 2018 were also showed as the range of 0.93-3.39 mg/kg. As concerns over the spread and high concentration of marine biotoxins due to recent climate change, the improvement of monitoring and safety management for shellfish toxins are consistently required.
In this study, we conducted a larval breeding study of Tresus keenae using 5 Bacillus genera, which are excellent in the ability to decompose high molecular weight organic matter and the antibacterial activity of pathogenic bacteria, among the 65 Bacillus genera. Research results that the relationship between larval growth and viability was high in the TKI42 and microbial mixed strains of TKI02 + TKI14 + TKI26 + TKI32 + TKI42. The growth and viability of larvae at the amount of the mixed microbial strain (TKI02 + TKI14 + TKI26 + TKI32 + TKI42) was 1.0×106 CFU/ml, which was the best growth, and 1.0×107 CFU/ml, which was the lowest. And the survival rate was the best at 1.0×105 CFU/ml. In addition, the growth and survival rate were high when the mixed microbial strain (1.0×106 CFU/ml) with a water temperature of 25°C was treated. In this study, when the growth and survival of larval breeding was investigated based on five Bacillus strains, the prediction of the application to the breeding of organisms in the aquaculture industry based on the special ability of a single strain is uncertain. Rather than developing and using only a single strain, it is thought that the effect can be expected to using mixed strains.
Long-term growth and survival rates were investigated in stocking size of Haliotis discus hannai seeds in sea cages. This study was conducted at the abalone cage culture in Bogil-do, Wando-gun, Jeollanam-do. The cage used in the experiment was 2.4 m × 2.4 m, and Undaria pinnatifida and Saccharina japonica were supplied as diet. The size of sea cage stocking seeds was divided into groups A (3.2 to 3.6 cm), B (2.9 to 3.2 cm), C (2.6 to 2.9 cm), and D (less than 2.6 cm) based on each Shell length. During the experiment, the salinity and pH were maintained at constant values, and the water temperature and dissolved oxygen content showed seasonal changes, but they were suitable for rearing abalone. As a result of rearing for 722 days, the survival rate did not show a significant difference between the experimental groups except for group D, which was excluded from the experiment due to the large number of early mortality when the cage was stocked. The growth of seeds gradually narrowed as the rearing period lengthened after stocking at sea cages, and there was no significant difference between A, B, and C after 722 days. In conclusion, it was found that the stocking size of early seeds did not affect productivity during long-term rearing.
Winter mortality of blood cockles (Tegillarca granosa) is a one of the main concerns of cockle aquaculture in Korea. Thus, this study investigated the physiological alternation of the cockles when they were placed in abnormally cold temperature. For this purpose, cockles were exposed to temperatures of 4°C (control), 2°C, 0°C, –2°C, and –5°C for four hours/day over eight days, and the condition index, nitric oxide concentration, and mortality rates were measured after each cold treatment. The results showed that the cockle nitrite concentration increased significantly in all groups, except for the control group, from the 1st day of exposure, and that this NO increase continued until the end of the experiment. In addition, cockles exposed to –5°C for 5 days showed an increase of mortality rate. These results suggested that cockles were experienced a physiological stress when they were exposed to < 2°C and might have resulted in mortality under severe hypothermic condition in winter. Our study also suggested that the measured NO concentration in the hemocytes of cockles is an efficient biomarker for diagnosing physiological stress in cockles exposed to cold shock.
Empty shells of seven species of bivalve mollusks with attached algae, predominantly Ulva linza L., were found intertidally in Sishili Bay, Yantai (Yellow Sea), out of total 17 species collected. Quantitative characteristics of shells and algae, including weight, size and shell/algae weight ratio are provided. Observations show that mass algal attachment may facilitate shell dislodgements leading to transportation of selected species and environmental mixing in thanatocoenoses. Molluscan shells serve as an additional substrate for green algae, thus, it may increase their abundance in shallow waters.
