1983 Volume 1983 Issue 24 Pages 60-68
Analytical study was carried out on the factors which regulate the ecological distribution of the mobile polychaete Armandia sp. on an intertidal sand flat. The larval settlement on the particular zones of the flat. is determined by the three processes: passive accumulation of the larvae by slowdown of the transporting force of the water current or the wave, active selection of the substratum by the settling larvae, and predation by the hermit crab pioaenes nitidimanus and exclusion by the ghost shrimp Callianassa japonica. In the summer season when the sea water on the flat is calm, the subsequent population movement after settlement on the flat can be regarded as a random dispersion process on a one-dimensional space with an incomplete reflection boundary due to sand ejecting activity of Callianassa. In winter when the northery wind prevails, the vigorous incoming waves together with the flow tide expel the animals from the surface of the sand and carry them to the landward end of the flat.