Alongshore configuration and size of local populations of the callianassid shrimp Nihonotrypaea harmandi (Bouvier, 1901) (Decapoda: Thalassinidea) in the Ariake-Sound estuarine system, Kyushu, Japan

In the Ariake-Sound estuarine system, intertidal sandflats or sandy beaches inhabited by Nihonotrypaea harmandi are distributed along the western half of the coastline. In these habitats, the ghost shrimp occupies zones or patches mostly composed of moderately (well) sorted fine sand. A previous study has identified 38 local shrimp populations along the coastline. Of these, 26 main populations were surveyed to estimate their sizes prior to the breeding season in 1998. For each location, the shrimp-inhabited zones/patches were mapped, and density was assessed by counting the number of burrow openings at a number of stations. The total number of shrimps at each zone/patch was estimated by multiplying the mean shrimp density by its area. The entire population size was given as the sum total of those from all zones/patches. Of all local populations, the population size on one sand flat situated at the southwestern periphery of the target waters was by far the largest due to both the highest density and the largest area, accounting for 70% of the total number of shrimps in the estuarine system. This sand flat is closest to the largest larval retention ground in the waters lying 10 to 20km offshore