Changes in density and culture conditions of the Manila Clam Ruditapes philippinarum on the West coast of Korea

Changes in density of manila clam, Ruditapes philippinarum to environment, catch and recruitment were studied in a few stations (Seonjae, Seongam, Hwangdo and Padori) in the West coast area of Korea from January, 2007 to December, 2009. Water temperature, salinity, dissolved oxygen and pH in the study stations were 0.8 to $31.2^{\circ}C$, 22.1 to 33.7 psu, 5.0 to 12.0 mg/L and 7.39 to 8.99, respectively. The concentrations of dissolved inorganic nitrogen, phosphate and silicate were 0.016 to 1.281 mg/L, 0.004 to 0.093 mg/L and 0.016 to 1.617 mg/L, respectively. Chlorophyll-a ranged from 0.2 to 12.1 ${\mu}g/L$, respectively. Substrata were mainly composed of muddy sand and very poorly sorted in Padori, muddy sand and well sorted in Seonjae and Hwangdo, gravelly muddy sand and poorly sorted in Seongam. Density was high in Seonjae and Seongam, but low in Hwangdo and Padori. In clam culture station, in which spat was naturally produced without sowing seedlings, the living density was decreased by increasing of death and a catch of shellfish, and recruitment was changed. Also, Density affected condition factor and shape of clam. Condition factor was the highest in Hwangdo, in which temperature in the winter and chlorophyll-a were high, and was the lowest in Padori. In the shape of clam, the shape in Seongam was a elongated form, but in Padori was a stunted form.

서해안 바지락 양식장의 서식환경과 서식밀도의 변화

서해안 4개 지역 바지락 양식장의 저질조성에 따른 바지락 형태적 특성에 관하여 조사하였다. 조사기간 동안 수온은 $0.8-31.2^{\circ}C$ 범위로 나타났으며, 염분은 22.5-33.7 psu, 용존산소는 4.4-12.0mg/L, pH는 7.39-8.99였다. 질소는 0.016-1.206mg/L, 인은 0.004-0.090mg/L, 규소는 0.016-1.592mg/L로 나타났다. 클로로필-a는 0.2-12.1 ${\mu}g/L$로 나타났다. 저질조성은 파도리는 니사질로 분급이 매우 불량하였으며, 선재와 황도는 니사질로 분급이 양호하였으며, 선감은 역니사질로 분급이 불량하였다. 서식밀도는 저질조성에 따라 선재와 선감에서 높았으며, 황도와 파도리에서 낮게 나타났다. 치패가 자연발생하여 씨뿌림이 없는 바지락 양식장에서 서식밀도는 폐사, 어획에 따라 감소하고, 전년도의 서식량에 따라 가입량은 변화하는 것으로 나타났다. 또한 서식밀도는 비만도와 바지락 형태에도 영향을 미치는 것으로 나타났다. 비만도는 겨울철 수온이 높고 먹이생물인 클로로필-a가 높았던 황도에서 가장 높게 나타났으며, 선재와 선감은 비슷하였고 파도리에서 가장 낮게 나타났다. 형태적 특성에서 선감이 가장 장형이었으며, 파도리는 단형에 가까웠다.