In order to elucidate the influence of large winter waves on the mortality of Japanese littleneck clams(Ruditapes philippinarum), we conducted surface exposure experiments using seawater tanks in summer and winter. Clams were manually exposed to the seabed surface with different frequencies, and their burrowing rate, glycogen content and condition factor were found to be negatively correlated with the frequency of the exposure in both seasons and the values were lower in winter than in summer. These results show that repeated surface exposure reduces glycogen content and condition factor and results in a lower burrowing rate. Moreover, its influence is more severe in winter. In the winter experiment, some clams on the surface burrowed and then crawled out. The clams that crawled out had much lower glycogen contents(less than 10mg/g), than those that burrowed, indicating that they were weakened. These results suggest that exposure to large winter waves leads to the death of the clams.
