| Abstract |
Based on plankton samples collected in the summer of 1998, larval abundance patterns for three species of Nihonotrypaea were examined in relation to the intertidal habitats of adults (N.japonica: sand flats in the enclosed estuary of Ariake Sound; N.harmandi: sand flats from outer third of Ariake Sound to waters of intermediate character of Tachibana Bay, to open sea (East China Sea); and N.petalura: shingle beaches in same waters as for N.harmandi).N.petalura larvae comprised only 7% of the sample, reflecting the lower density of adults.Z1 of N.japonica and N.harmandi occurred from Ariake Sound to mostly northern Tachibana Bay, and from Ariake Sound to the entire Tachibana Bay, respectively.It is suggested that 1) with progression of larval stages (up to Z5), both larval species remained in Ariake Sound, while most disappeared from northern Tachibana Bay; and 2) larvae of N.harmandi were retained in the southern Tachibana Bay.The mechanism of larval retention in Ariake Sound is unknown.Oceanographic data collected from Tachibana Bay indicated a time-averaged westward current originating from Ariake Sound in the northern part, and a time-averaged eastward current originating from the East China Sea in the southern part, with an estuarine front often formed between north and south.This could explain the disappearance (probably by flushing) and retention of larvae in each part of Tachibana Bay.The distribution for adults of the three species in this estuarine system reflects abundance patterns of their larvae |
