Effect of water flow on larval settlement in the nagura amparu tidal lagoon

Abstract

This study analyses settlement process of megalopa, which is final stage of crab larva, on a tidal lagoon based on population sampling of juvenile crabs and numerical simulation of larval settlement. Population sampling was carried out 3 times in settlement period, detailed distribution of the juveniles were grasped. The observed results indicated many megalopae have settled down at around points of 0.2 meters elevation. In addition, it seemed that the positions where many juveniles inhabited are near stagnation point. Then, to grasp the relationship between larval settlement and flow field, numerical tracer chasing by 2-D Lagrangian model was conducted. This study brought up tractive force as settlement parameter of tracer. By comparison the distribution, the calculated result with considering tractive force agreed with the observed result. Additionally, the results in spring tide are more reasonable than neap and middle tides, thus, megalopae may reinvade to the lagoon and settle down in the spring tide practically.