Effects of Size and Environmental Condition on Burrowing of Artificial Seedling of Ark Shell, Scapharca broughtonii  (Schrenck)
Byeong-Hak Kim, Yun-Kyung Shin, Nack-Joong Choi, Bong-Se Oh, Sang-Gyu Sohn, Choon-Goo Jung, Tai-Sun Son and Kyoung Ho Kang
South Sea Mariculture Research Center, NFRDI, Namhae, 668-821, Korea
The influence of individual size, sediment, gain size, water temperature, salinity and air exposure on burrowing rate was investigated in order to obtain the basic biological data on applying shellfish farm for a sustainable production of ark shell, Scapharca broughtonii (Schrenk). The burrowing rate on individual size 300 minutes after starting the experiment was the highest in the shell length 16.3 ¡¾ 1.2 mm, 97.7%. The highest burrowing rates were 97.0% in 12.8 ¡¾ 0.8 mm, 96.7% in 9.2 ¡¾ 1.0 mm, and 96.3% in 5.9 ¡¾ 0.7 mm. The clams over 6 mm of shell length had burrowing ability and the burrowing rate was not related to the shell size. The burrowing rate depending on the kind of grain at the bottom after 300 minutes was the highest, 98.3%, in the mixture of sand and silt with a ratio of 75:25. The rates were 98% in silt (100%), 97.3% in mixture sand and silt with a ratio of 50:50, 97.3% in sand and silt ratio of 25:75, and 86.3% in sand (100%) in this specific order. On grain size of the soil in the seafloor, the burrowing rates after 300 minutes was at its highest in the group of sand in pore size 1 mm with 85.0%, and the 12 ¥ìm to 1 mm in the grain size was fitted to burrowing of artificial seed. In the case of water temperature, the burrowing rates were at its highest after 300 minutes. In 30¡É group, the rate was 96.7% and in 25¡É and 20¡É, 90.0%. The rates decreased as the water temperature decreased below 15¡É. The burrowing rates on salinity were the highest in 30 psu with 93.3% and at 15 psu and below, there was no noticeable change in the burrowing rate. On air exposure, the burrowing rates after 300 minutes were the highest in 1 hour with 93.3%, and remarkably decreased as air exposure time is longer after 12 hours of air exposure.
  
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