Effect of sand supplement and plowing on the occurrence of natural manila clam (Ruditapes philippinarum) spats in the tidal flat of Geunso bay, Taean-gun, Chungnam province, on the west coast of Korea
Jun-Hyeop Jeon, Hee-Do Jeung, Kwang-Jae Park, Kyu-Hyun Lee, Hyun-Mi Ahn, Hee-Jung Lee, Yoon-Seok Choi, Jae-Hee Song and Hee-Woong Kang
Tidal Flat Research Center, National Institute of Fisheries Science (NIFS), Gunsan 54001, Republic of Korea East Sea Fisheries Research Institute, NIFS, Gangneung 25435, Republic of Korea Southeast Sea Fisheries Research Institute, NIFS, Tongyeong 53085
This study was carried out to investigate the effects on the occurrence of clam spats resources by sand supplement and plowing at the natural seedling fields of manila clam (Ruditapes philippinarum) in Geunso bay, Taean-gun, of the west coast of Korea. The sand addition and plowing were conducted on the tidal flats of Pado-ri and Beopsan-ri in Geunso bay in August 2013. We monitored the variation of newly recruited clam spats (shell length (SL ≤ 5 mm), adult clams (SL ≥ 10 mm) and the change of sediment from January 2014 to December 2015. In the Pado-ri tidal flats (with 2-4 hours mean air-exposure time), the density of newly recruited clam spats in the experimental site (sand added) was higher 1.5-4.0 times than that of control (sand not added) from October 2014 to April 2015. And the highest clam density was 25,750 ± 1,708 clams per square meter in January 2015. The density of adult clams in Pado-ri was also higher in the experimental site than control until June 2015. However, despite lots of juvenile clams (SL ≤ 20 mm) were observed in control site, adult clam density in Pado-ri has changed from July 2015 due to decrease of sand proportion in sediments. In Beopsan-ri experimental site (with 4-6 hours mean air-exposure time), the newly recruited clam spats was less than 3,000 clams per square meter, which was lower than control. As the results of the study, it seems that clam spats increased by sand addition and plowing are likely to be decreased in a short period of time due to deposition of fine sediment and other adverse environments (such as long air-exposure time). Therefore, it seems to be necessary to examine carefully the various environmental factors before trying to improve the environment of natural clam seedling beds by sand supplement and plowing.
  
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