Spawning period estimation of the manila clam Ruditapes philippinarum based on the recruitment samples from Seonjae-do tidal flat, Korea

초록

This study was carried out to estimate the spawning period and recruitment of the manila clams from Seonjae-Do in the west coast of Korea, based on their settlement and recruitment data. The monthly sampling was conducted from September 2008 to August 2009 at two stations for two populations, one for adults using 10 x 10 cm quadrat and the other for initially settled recruits using 3.5cm corer in diameter. Five to ten replicates per station were sampled for adults and these data were later used for the condition index. Based on the presence of the initially settled recruits and the condition index, the spawning period of the manila clams in Seonjae-Do was estimated from June to October and the main period was between July and September. The main recruitment occurred in spring but a few were also observed in fall. The recruitment in spring born by the spawners of the previous year settles and spends the winter time without significant growth but they start to grow in next spring with the temperature rise. However, the recruitment in fall occurs by the settlers with rapid growth born from the spawners of the year. Consequently, the manila clams in Seonjae-Do tidal flat spawn between July and September, settled and spend the winter time in a small size. But, they start to grow in next spring, reach 22mm in shell length and in the second year they grow to 30mm in shell length and matured and spawned.