Abstract
During the period 1991–1992, we examined temporal fluctuations in densities of the native and exotic mytilids Musculista senhousia and Xenostrobus securis in the brackish Lake Hamana on the Pacific coast of central Japan, using cohort separation of planktonic stages and benthic stages (i.e., new settlers and small individuals). Temporal fluctuations in densities of both planktonic and benthic stages were similar between the two species. However, the densities of benthic stages were much higher for M. senhousia than for X. securis. There was a similar trend of variation in densities of benthic stages among sampling sites for each mytilid. This suggests that microhabitat separation of large individuals (≥ 1.0 mm in shell length) between these two species may be determined at the post-recruitment stage, when X. securis individuals with shell lengths of ≥ 2.0 mm probably immigrate into the study area from other areas.
