• The Korean Journal of Malacology
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• v.26 no.3
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• pp.227-234
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• 2010

A comparative analysis of size and age structures of coastal subfossil shell assemblages of the shortnecked clam Ruditapes philippinarum from open and protected bays of Cheju Island (Korea) was carried out. On the whole, taking into account the damage of small fragile shells, size and age structures of the shell assemblages corresponded to the classical curve of bivalve population distribution when its mortality diminishes with age increase up to a certain threshold. It was found that shell samples from open bays of the western, southern and eastern coasts included shells of smaller and younger individuals (L ${\leq}$ 40 mm, ${\leq}$ 4 years) than samples from the eastern protected bay (L ${\leq}$ 54.5 mm, ${\leq}$ 6 years). Evidently, strong wave activity was the reason for a short life-span of the clams from the open areas. Growth was investigated retrospectively by annual growth rings on the shells. Growth rates of the clams from the various coasts of Cheju Island differed. However, growth rates of the clams from different biotopes at the same (eastern) side of the Island were similar. Shell height/length and width/length ratios statistically significantly increased with the clam age increase. Most likely, the reason for such shell shape alteration is that more conglobated individuals more survive being more energy-optimal than oblong specimens.

• The Korean Journal of Malacology
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• v.26 no.3
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• pp.185-199
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• 2010

Correlation between community structure of herbivore and succession of macro-algal flora was examined in subtidal area of Dang-Sa Province, eastern coast of Korea from April 2008 to December 2009. For examination, the authors hypothesized that there are significant correlation between the foregoing two variables. Samplings were conducted every two months quantitatively with SCUBA diving at -3, -6 and -10 depth in the two line transects (barren and forest grounds). As results, rhodophyts was predominated in the algal flora based on the number of species and biomass; molluscs was predominated in the herbivores based on the number of species and echinoderms was predominated in that based on the biomass. There was no significant correlation between the foregoing two variables in the whole survey area and barren/forest grounds. Consequently, the hypothesis was rejected. The authors proposed that examination of correlation between the foregoing two variables should focus on the specific herbivore group(s) (e.g., amphipods) afterward.

• The Korean Journal of Malacology
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• v.26 no.3
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• pp.179-183
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• 2010

In other to understand the effect of yellow soil to mortality of Korean scallops, P. yessoensis, We investigated its mortality at indoor tanks. The environmental conditions such as water temperature, Salinity, Do and pH were continued constantly during the experimental periods. The 100% of survival rate showed in two experiments groups such as 0.1% and 0.4% of concentration of yellow soil and the other groups as 0.05% and 0.2% of concentration of yellow soil was appeared one dead scallop at each group for 8 days of the experiment periods. the gills of scallop in high concentration of yellow soil (0.2% and 0.4% groups) were covered by yellow soil particles so that this group's scallop should be got a high stress from yellow soil. I think this situation will be more continued for long time the scallop will become to dead. The results of bacteriological analysis did not isolated from haemolymph of scallops and no Perkinsus infectious disease in scallops and the scallops showed necrosis and degeneration on digestive grand and gills of scallop.

• The Korean Journal of Malacology
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• v.29 no.3
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• pp.245-250
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• 2013

We investigated the factors of mass-mortality in terms of water temperature and prey, in order to prevent the mass-mortality of cultured oysters at Gamak Bay in Yeosu City in 2007. The real-time water temperature was recorded as high, 28 to 31C, during late August. Nutrients, Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phosphate (DIP) were downed in September. The analyzed results of chlorophyll a content were 0.78-1.50 ${\mu}gL^{-1}$ and phytoplankton for food resources was 81 cells $mL^{-1}$, both were low. The finding here indicate that Gamak Bay is in an oligotrophic state. The mass-mortality of cultured oysters occurred 43.6% in Gamak Bay. The mortality rate of oyster were above 67.0%, at Wanpo, however, it was showed 18.3% at Gumchun. Therefore, we believe the mass-mortality of cultured oysters at Gamak Bay comes from the destruction of bio-rhythms due to high water temperature and quantitatively and qualitatively decreasing food resources due to the limitation of nutrients.

• The Korean Journal of Malacology
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• v.29 no.3
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• pp.239-244
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• 2013

Mass mortalities of farmed shellfish, mostly in summer season, thus named mass summer mortalities, have been a global issue in shellfish aquaculture. The 2013 mass summer mortalities in the confined waters of Goseong Bay, Goseong, Korea were quite a unique and intensive for two farmed species, the Pacific oysters, Crassostrea gigas, and bay scallops, Argopecten irradians. The mortalities were progressive from the bottom of the suspended oysters and caged scallops in the waters, reaching up to 80% for the oyster and 95% for the scallop in about 20 days after the first occurrence, early August, 2013. We monitored a wide range of environmental factors, including water temperature, dissolved oxygen (DO), salinity, turbidity, acidity (pH), organic and inorganic matters, chemical oxygen demand (COD), suspected pathogenic agent, and phytoplankton composition throughout the water column where the two species were suspended or caged. Our survey concluded that the hypoxia or anoxia might be a major cause of the mortalities. Here, we detailed the mortalities and ways to arrive at the conclusion.

• The Korean Journal of Malacology
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• v.29 no.3
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• pp.217-223
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• 2013

The morphological relations and physiological characteristics of the triploid and diploid oysters (Crassostrea gigas) in Taean area, west coast of Korea, were investigated from May 2012 to April 2013. Mophometric analysis indicated that the triploid oysters have the same shell length to shell height ratio but higher shell depth to shell height ratio than diploids. Consistent with morphological characteristics, triploid oysters showed greater values of fatness, condition index and RNA/DNA ratio during the period of experiment. The DNA concentration in adductor muscle and mantle of triploid were either lower or equal to the nucleic acids of diploid. However, RNA/DNA ratio were significantly higher than diploid. It appears that RNA/DNA ratio could be a useful indicator of health condition of triploid and diploid oysters when taken in correlation with the morphological indices.

• The Korean Journal of Malacology
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• v.29 no.3
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• pp.163-169
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• 2013

In the present study, the seven primers BION-33, BION-34, BION-37, BION-41, BION-44, BION-45 and BION-42 generated the total number of loci, average number of loci per lane and specific loci in Hongseong, Yeosu and Goheung population of F. mutica, respectively. 7 primers generated 19 specific loci in the Hongseong population, 29.3 in the Yeosu population and 23.1 in the Goheung population, respectively. Especially, the decamer primer BION-37 generated 7 unique loci to each population, which were identifying each population, approximately 700 bp in Hongseong population. In this study, the dendrogram obtained by the seven primers indicates three genetic clusters: cluster 1 (HONGSEONG 01-HONGSEONG 07), cluster 2 (YEOSU 08-YEOSU 14) and cluster 3 (GOHEUNG 15-GOHEUNG 21). Among the twenty one cockles, the shortest genetic distance that displayed significant molecular differences was between individuals 17 and 19 from the Goheung population (genetic distance = 0.051), while the longest genetic distance among the twenty-one cockle individuals that displayed significant molecular differences was between individuals HONGSEONG no. 03 and YEOSU no. 12 (genetic distance = 0.616). Relatively, individuals of YEOSU population were fairly closely related to that of GOHEUNG population. Ultimately, PCR fragments revealed of in this study may be useful as a DNA marker the three geographic populations to distinguish.

• The Korean Journal of Malacology
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• v.30 no.2
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• pp.127-134
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• 2014

Gonad maturation of Manila clam, Ruditapes philippinarum was induced in this study using a recirculation system over 8 weeks in early spring. Clams used in the experiment were collected in $15^{th}$ April 2010 from the west coast of Korea, as the surface water temperature remained $11^{\circ}C$. To induce gametogenesis and subsequent maturation seawater temperature was elevated $1^{\circ}C$ per day over 10 days to reach $20^{\circ}C$. For the experiment, clams were raised in 120 L quadrangle tank maintained with re-circulated seawater system over 57 days. Water quality parameters including the water temperature, salinity dissolved oxygen, ammonium ion and nitrate levels in the tanks were monitored daily. Mixture of concentrated microalgae including Tetraselmis, Isochrysis, Pavlova and Thalassiosira weissflogii was supplied to clams twice a day, and quantity of the daily ration was adjusted as 3% of clam body dry weight. Histology was applied to examine gonad maturation. Daily monitoring of the water quality parameters indicated that the recirculation system supplied suitable environment to Manila clam; the nitrogenous components stayed below toxic levels (< 0.2 mg/L). At the beginning of the study, clams were mostly in early developing stage. As the seawater temperature reached $20^{\circ}C$, 10 days after the experiment, 20% of clams reached late development at 12 days. First ripe clams were observed at 42 days and 40% of clams were in ripe and ready for spawning at the end of study, 57 days after the experiment. In this study, gametogenesis of Manila clam was successfully induced by elevating water temperature and supplying commercially produced microalgae in a recirculation tank system.

• The Korean Journal of Malacology
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• v.30 no.2
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• pp.139-153
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• 2014

We investigated fecundities in egg capsules and sizes at 50% of group sexual maturities in female Rapana venosa in three different salinity concentration regions (S-1, S-2, and S-3). In three different salinities, egg capsule heights, the number of egg capsules and the number of eggs and embryos were remarkably increased with the increase of female shell heights (or ages) and also increased with the increase of salinity concentrations. Heights of egg capsules, the number of egg capsules and fecundities (the number of eggs and embryos) were the maximum at S-1 (Gwangyang Bay (average 31.5 psu)) and the minimum at S-3 (the upper reaches of Seomjin River (average 15.5 psu)). Total numbers of fecundities of R. venosa $individual^{-1}year^{-1}$ were about $1{\times}10^6$ at S-1 region, about $8{\times}10^5$ at S-2 region, and about $2{\times}10^5$ at S-3 region. Rates (50%) of individuals reaching first sexual maturities in three different salinity regions (S-1, S-2 and S-3) were over 50% in females measuring 7.1-8.0 cm in shell height (considered to be two years old), and 100% in those > 10.1 cm (considered to be five years old). Biological minimum sizes ($RM_{50}$) in females in three different regions are 72.0 mm SH at S-1 region, 70.9 mm SH at S-2 region, and 74.6 mm SH at S-3 region, respectively. Exceptionally, smaller individuals (considered to be one year old) were participated in reproduction.

• The Korean Journal of Malacology
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• v.30 no.2
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• pp.101-106
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• 2014

Clearance rate and feeding of surf clam, Mactra veneriformis were determined for 5 different water temperature regime (5, 10, 15, 20, $25^{\circ}C$) and salinity regime (8, 14, 20, 26, 32 ‰) with small group ($86.62{\pm}7.10mm$ in shell length) and large group ($147.99{\pm}10.83mm$ in shell length). Clearance rate and feeding increased with water temperature up to $20^{\circ}C$, but rapidly decreased at $25^{\circ}C$. The minimal clearance rate and feedign was recorded at $5^{\circ}C$. surf clam showed low clearance rate and feeding at low salinity (below 20 ‰) and maximum values at high salinity (26-32 ‰).