抄録
To find a means of restoring the population of the clam Meretrix lusoria, we caged M. lusoria and three other clam species at two stations on the Oi tidal flat in Tokyo Bay, where hypoxic water often intrudes. Nine caging experiments, each of which lasted for 1.5 to 5 months, were conducted from July 2006 to October 2007. The survival and growth of the clams in relation to environmental conditions were assessed. M. lusoria showed high mortalities (survival ≈ 40%) at the muddier station in the late summer of 2007, when hypoxic water was consistently present in the shallow subtidal zone. However, its survival rates exceeded 90% in all other cases, and were higher than or comparable to those of the other species throughout the study period. The growth rates of M. lusoria in warm seasons were higher than or comparable to those of the other species, and were less affected by sediment quality than those of Mercenaria mercenaria, the predominant species on the flat. Thus, M. lusoria had a high survival ability, and other factors such as overfishing and life-cycle-related events should be considered for restoration.
