LARVAL ABUNDANCE PATIERNS FOR THREE SPECIES OF NIHONOTRYPAEA (DECAPOD A: THALASSINIDEA: CALLIANASSIDAE) ALONG AN ESTUARYTO-OPEN-SEA GRADIENT IN WESTERN KYUSHU, JAPAN

Abstract

Based on plankton samples collected from an estuarine system in western Kyushu, Japan, in summer, I 998, larval abundance patterns for three species of Nihonotrypaea were examined in relation to the intertidal habitats of adults [N. japonica—sandflats within the enclosed estuary (= Ariake Sound); N. harmandi—sandflats in the area from the outermost part of Ariake Sound through the waters of an intermediate character(= Tachibana Bay) to the open sea(= the East China Sea); and N. petalura—boulder beaches in the same waters as in N. harmandi]. Largely, the distribution for adults of the three species reflected abundance patterns of their larvae. Larvae of N. petalura comprised only 6% of the sample, reflecting the lower abundance of adults. Zoea 1 of N. japonica and Zoea I of (N. harmandi + N. petalura) occurred from Ariake Sound to mostly the northern Tachibana Bay and from Ariake Sound to the entire Tachibana Bay, respectively. It was suggested that 1) with the progression of larval stages for 15-19 days (up to Zoea 5), the three larval species remained in Ariake Sound, while most of them disappeared from the northern Tachibana Bay; and 2) larvae of N. harmandi and N. petalura were retained throughout development in the southern Tachibana Bay, which corresponded well to the largest local adult populations of each species occurring along the northern coast of an island in the southern Tachibana Bay. Possible mechanisms generating the larval abundance patterns are discussed in relation to the oceanographic conditions of the estuarine system.