Numerical simulation for larval connection network of the ghost shrimp Nihonotrypaea harmandi population among intertidal sandflats in Tachibana Bay and Ariake Sound, western Kyushu, Japan

摘要

In Tachibana Bay and the outermost one-third of Ariake Sound, western Kyushu, Japan, there are a number of intertidal sandflats inhabited by the ghost shrimp Nihonotrypaea harmandi (Decapoda: Thalassinidea: Callianassidae). An intertidal sandflat facing Tomioka Bay (Tomioka tidal flat), situated at the southwestern periphery of Tachibana Bay, has a much larger shrimp population than the other tidal flats, accounting for 70% of the total number of shrimps in the region. It is anticipated that exchange of planktonic larvae will occur among local shrimp populations. The purpose of this study was to clarify the larval connection network of N. harmandi among the 26 main local populations in the region by using a numerical tracer model. Our numerical model included vertical migrations of N. harmandi larvae, based on observations of larval vertical distributions. From the viewpoint of the larval supply and reception relationships, the local populations were subdivided into four groups. The first group exchanges larvae with the Tomioka tidal flat population. The second group receives larvae from the Tomioka tidal flat population but does not supply larvae to the latter. The third group supplies larvae to the Tomioka tidal flat population and the first group but does not receive larvae reciprocally. Although the last group supplies larvae to a part of the first group and the third group, it does not have a reciprocal relationship with the Tomioka tidal flat population. In terms of larval flux, the Tomioka tidal flat population was concluded to be the center of the larval connection network in the region.