• Journal of Aquaculture
• /
• v.19 no.4
• /
• pp.236-241
• /
• 2006

Seasonal variation of the infection by three species of symbiotic copepods in clam, Tresus keenae was investigated in south coast of Korea. The prevalence and abundance of three symbiotic copepods showed seasonal variation with a peak in winter. Reproduction of the copepods occurs from early autumn to spring as indicated by higher ratio of gravid copepods. The frequency distribution of Lichomolgus inflatus, Pseudomyicola spinosus and Anthessius progectus in their host population could be fitted with negative binominal distribution. Results from the present study suggest that seasonal fluctuation in prevalence, relative density and mean intensity is related to temperature and life history of the symbiotic copepods.

• The Korean Journal of Malacology
• /
• v.21 no.1
• /
• pp.65-70
• /
• 2005

The purpose of this study is to determine the appropriate substrate for larval settlement and spat growth in the purple clam, Saxidomus purpuratus in laboratory culture. Larvae were reared with 3 different types of sediments (mud, sand, and mixed) for 46 days in settlement experiment, and settled spats were further grown in 3 types of sediments for 36 weeks in growth experiment. The density of settled spats in muddy sediments was more than 2 times higher than those in mixed or sandy sediments. But, the average size of settled spats in muddy sediments was smaller than those in mixed or sandy sediments. After 36 weeks of growth period, growth rate decreased as shell length increased. When shell length was less than 2 mm, growth rate in mixed sediments was significantly higher than that in sandy sediments. When shell length was more than 2 mm, there was no significant difference in growth rate among different substrates. Sediment type affected growth rate only when the spats were relatively small (less than 2 mm). Muddy sediments seems better for larval settlement, while mixed sediments is best for spat growth. We suggest the laboratory procedure for enhancing seedling production of S. purpuratus.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.49 no.3
• /
• pp.351-358
• /
• 2016

The aim of this study was to verify the performance of Teleaulax amphioxeia as prey for Brachionus plicatilis and for the larvae of the bivalves (Pacific oyster Crassostrea gigas and Manila clam Ruditapes philippinarum) to select the best of five T. amphioxeia strains. The five strains of T. amphioxeia were collected from the coasts of Korea, purecultured and then fed to the rotifer and bivalve larvae. The density and fecundity rate of the rotifer fed on strain 01 were the highest. The instantaneous growth rate of the rotifer fed strain 08-2 was the highest. The maximum density and fecundity rate of the rotifer fed strain 08-2 were significantly higher than those fed Chlorella ellipsoidea, while instantaneous growth rate showed the opposite pattern. Survival rates of the Manila clam larvae fed each strain of Teleaulax showed no significant difference between strains. Survival rates of the Pacific oyster fed Teleaulax were significantly higher than those fed Chaetoceros sp., but lower than those fed I. galbana. This study indicates that strain 08-2 showed better growth for B. plicatilis and better survival for the bivalve larvae than did the other strains, and that T. amphioxeia can also be used as a prey organism for rotifers or bivalve larvae.

• The Korean Journal of Malacology
• /
• v.26 no.4
• /
• pp.303-310
• /
• 2010

Rearing condition and species of microalgae on growth and survival of the sunray surf clam, Mactra chinensis larvae were investigated for artificial seedling production. The larvae of M. chinensis on higher temperature showed high growth and low survival and was grown over $230{\mu}m$ in shell length 14 days after hatching, but low growth as $151.1{\mu}m$ at $18^{\circ}C$. The larvae of M. chinensis on salinity showed highest daily growth and survival as $11.3{\mu}m$ and 65.8% at 30 psu, respectively. The optimum of water temperature and salinity for the larval rearing were $23^{\circ}C$ and 30-35 psu over 25 psu at least. The density of larval rearing was below 10 per 1 ml in rearing seawater for elevating the development rate from D-shaped to settled (metamorphosing) stage. The larvae fed the mixed diet of Isochrysis galbana, Pavlova lutheri, Isochrysis sp. (green), Chlorella ellipsoidea showed highest growth and survival. The larvae fed the single diet of I. galbana, Isochrysis sp. (green) showed high growth and survival. But the larvae fed the single diet of P. lutheri and C. ellipsoidea showed low growth and survival. The optimum diet of larvae of M. chinensis was over two species of microalgae included I. galbana, Isochrysis sp. (green) for elevating the high growth and survival.

• The Korean Journal of Malacology
• /
• v.26 no.4
• /
• pp.297-302
• /
• 2010

Water temperature, salinity and density on egg development of the sunray surf clam, Mactra chinensis were investigated for artificial seedling production. The required time from fertilization to D-shaped larvae were 33.8 hours in $18^{\circ}C$, 20.6 hours in $23^{\circ}C$, 18.2 hours in $28^{\circ}C$ and 15.0 hours in $33^{\circ}C$. The development duration was reduced with increasing temperature. The relationships between temperature and the required time from egg to each developmental stage were described as follows: 2-cell, 1/h = 0.1051WT - 1.4782; 8-cell, 1/h = 0.037WT - 0.3686; gastrula, 1/h = 0.008WT - 0.0521; trochophore, 1/h = 0.0041WT - 0.0235; D-shaped larva, 1/h = 0.0024WT - 0.0102. Biological minimum temperature for the egg development was estimated to be $8.0^{\circ}C$ in average. The possible range of temperature for the development of D-shaped larvae was $18-28^{\circ}C$ and optimum of water temperature for the development of egg was $23^{\circ}C$. The possible range of salinity for the development of D-shaped larvae was 20-35 psu and optimum of salinity for the development of egg was 30-35 psu over 25 psu at least. The density of fertilized egg was below 40 per 1 ml in rearing seawater for elevating the development rate from fertilized egg to D-shaped larva.

• The Korean Journal of Malacology
• /
• v.27 no.3
• /
• pp.167-173
• /
• 2011

This study was performed to describe the effect of water temperature, salinity and density on the eggs development of the hard clam, Meretrix petechialis. Eggs of Meretrix petechialis were turned out to be demersal isolated eggs of $82.3-86.1{\mu}m$ in an average diameter after spawning. The hatching rate of D-shaped larvae by elapsed time after spawning was the highest in fertilization immediately after spawning and distinguished decrease from 1 hour of spawning. The optimum water temperature for development of D-shaped larvae from fertilization was ranged between $25^{\circ}C$ to $27^{\circ}C$. However, D-shaped larvae was not developed at $33^{\circ}C$ of water temperature. The required time from fertilization to D-shaped larvae were 37.3 hours in $20^{\circ}C$, 20.8 hours in $25^{\circ}C$, and 15.3 hours in $30^{\circ}C$. Biological minimum temperature for the egg development was estimated to be $12.4^{\circ}C$ in average. The range of salinity for the development of eggs were 20.0-37.5 psu, optimum range was estimated to be 27.5-32.5 psu.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.23 no.7
• /
• pp.869-877
• /
• 2017

Recently, Gomso Bay saw a decrease in the production of manila clam, which accounted for 17.8 % of production across the whole country in 2015, while Geunso Bay saw an increase that raised its contribution to 49.1 %. The tidal flats in these bays are inhabited by various benthos, and material flows in and out according to the tide. It is essential to understand the mass balance of these regions while giving consideration to the characteristics of these tidal flats. In this study, we compared areas where aquaculture farms were located in Gomso Bay with those without from May to August 2015. We divided the region into three sea areas (Sector I, Sector II, and Control), and the mass balance was estimated using the LOICZ model. As a result, the DIP of Sector II in Gomso Bay and another region in Geunso Bay, where a manila clam farm was located, were found to be -207.2 kg/day and 77.2 kg/day. The DIN was -4,996.7 kg/day and 926.6 kg/day. These results suggest that Gomso Bay han a higher density than Geunso Bay, which is thought to be mainly due to the feeding action of organisms. Therefore, in order to maintain a healthy tidal flat ecosystem and to sustain the production of manila clams, sustainable management to reduce the high density of tidal flat farms is necessary.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.28 no.4
• /
• pp.143-157
• /
• 2023

This study confirmed the characteristics of macrobenthic community due to anthropogenic environmental changes in the Boryeong Jugyo tidal flat, where the habitat of manila clam (Ruditapes philippinarum) and mud shrimp (Upogebia major) is separated. The total number of occurring species was 55 during the study period with an average habitat density of 338 ind./m² and a biomass of 212.2 gWWt/m². The number of occuring species increased from 27 species at the upper flat to 37 species at the lower flat, and the dominant species differed by tide levels (Upper: Leonnates persica, Middle: Heteromastus filiformis, Lower: R. philippinarum). The macro-benthic community sturctures of the top 10 species using cluster analysis and nMDS were divided into two groups, focusing on Manila clam culture farm of lower flats and middle flats with high habitat density, reflecting the influence of specific species. The sediment composition of the U. major habitat space fluctuated highly, but it was maintained annually, and the sorting coefficient was 2.1 𝜑, and the proportion of the same particle size was increased. In particular, because the middle flat has a dense anthropogenic impact, a dominant species, H. filiformis dominated and revealed a relationship with the density of burrow holes of U. major, which is considered to be a biological interaction between these two macrofauna in this tidal flat.

• The Korean Journal of Malacology
• /
• v.24 no.2
• /
• pp.81-87
• /
• 2008

Distribution, population structure, and growth of the bivalve Protothaca euglypta were investigated for clams collected from the northwestern part of the East Sea of Russia. This species is distributed in further northern area than it was found earlier. In the southern area, this clam is found in the intertidal zone, up to 8 m in depth. It is one of the most numerous infaunal species of bivalves, and protected to wave action in the gravel-pebble and sand with rubble biotope. Population density of P. euglypta reaches 500 $spc./m^2$, and biomass 2 $kg/m^2$. Size and age composition of the local settlements and allometric growth of P. euglypta depend on a biotope. The growth rate of P. euglypta considerably reduces in case of the northern boundary area, whereas life span increases.

• The Korean Journal of Malacology
• /
• v.30 no.1
• /
• pp.95-99
• /
• 2014

In the present study, we surveyed the molluscan fauna in a lagoon located near Seong-san harbor on the east coast of Jeju Island in July 2012. For the survey, a $25{\times}25cm$ quadrat was deployed over 3 randomly selected sites in the intertidal area of the lagoon. Sediment from the surface to a depth of 25 cm in the quadrat was removed and sieved using a 1 mm mesh sieve. All molluscan fauna retained on the sieve was identified to the species level. From the survey, 25 species of mollusca belonging to 2 orders and 16 families were identified. Species richness, in terms of total number of species, was found to be the highest at sampling site 1, where the substrate was composed of coarse sand and some rocks, while it was lowest at sampling site 3, composed of compact fine sand. Regardless of the type of substrate at the sampling sites, the mud-creeping snail Batillaria cumingii (Crosse, 1862) occurred at a high density, ranging from $324-468ind./m^2$. The luciniid bivalve Pillucina pisidium also occurred at a high density at sampling site 1, at $336ind./m^2$, while the density of this species was only $4ind./m^2$ at sampling site 3. The Manila clam Ruditapes philippinarum could be found at all 3 sampling sites with very low density ranging from $16-48ind./m^2$. The density and species richness of molluscs observed in this study was lower compared to the previously reported molluscan fauna in Jeju Island, suggesting that further investigation needs to be carried out to conserve the unique marine lagoon ecosystem in Jeju Island.