Impact of low temperature during the winter on the mortality in the post-settlement period of the juvenile of short-neck clam, Ruditapes philippinarum, on the tidal flats in Hichirippu Lagoon, Hokkaido, Japan
2009
Komorita, T.(Hokkaido Univ., Sapporo (Japan)) | Shibanuma, S. | Yamada, T. | Kajihara, R. | Tsukuda, M. | Montani, S.
We conducted field surveys to monitor the population dynamics of short-neck clam, Ruditapes philippinarum, in Hichirippu Lagoon, in eastern Hokkaido, Japan, focusing on the negative impact of extremely low temperatures during the winter on juveniles in the post-settlement period. The clam population had a short annual breeding season between September and November. The newly settled juveniles experienced the severe winter as the daily mean temperature of the surface sediment descended below 0degC soon after settlement. The mortality of small juveniles (less than 3 mm in mean shell length) in the post-settlement period between October 24, 2006, and August 1, 2007, was estimated at 1.34%/d, which was approximately 5.6 times higher than after the post-settlement periods (0.24%/d and 0.17%/d). We compared the mortality of the juvenile in and after the post-settlement period with the results of the population study conducted on Kikuchi River Tidal Flat, Kumamoto, Kyushu (Tsukuda 2008), where the daily mean temperature was approximately 6degC higher in the post-settlement period of the juveniles. On Kikuchi River Tidal Flat, the mortality in and after the post-settlement period of the juvenile was estimated at 1.62%/d, and 0.49%/d and 0.44%/d, respectively. These facts indicate that the extremely low winter temperature in this study area (eastern Hokkaido) does not bring about large-scale mortality, and this is true not only for juveniles after the post-settlement period but also small juveniles in the post-settlement period.
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