We developed a numerical model for the advection of planktonic larvae of Manila clam (Ruditapes philippinarum) in Tokyo Bay that accounts for vertical migration, as well as individual differences in shell length and growth rates of larvae spawned on different dates. Using this model, we simulated the three-dimensional advection of Manila clam larvae in Tokyo Bay. The model was able to generally reproduce the observed larval movement, and the simulated final larval settlement locations were found to be consistent with results of young clam sampling.
The Manila clam (Ruditapes philippinarum), commonly known as " asari" in Japanese, is not only an essential component of the Japanese diet, it is also an environmentally important organism that plays a vital role in the water purification of tidal flats. Land reclamation in Tokyo Bay has dramatically reduced the area of tidal flats and shallows, which are the habitat of Manila clams. As a result, Manila clams now inhabit a patchwork of disconnected tidal flats and shallows between reclaimed areas. However, it is considered that a larval supply network connects these discrete habitats and that this network plays an important role in the survival of the Manila clam in Tokyo Bay.
Studies on the Manila clam populations in Tokyo Bay have included those undertaken as part of the " Asari Project" to monitor larvae in the entire Tokyo Bay area(2003); analysis of larval advection using numerical models and estimates of the larval supply network between habitats by Hyuga(2005); and the studies of Yagi et al.(2011). and Otsuka et al.(2010). However, the numerical models employed in these previous studies have treated Manila clam larvae as passive tracers that simply move with the current. Indeed, none of these studies has considered the active vertical migration of clam larvae.
