A new method to develop a dynamically stabilized aquatic environment to preserve functions of biotopes for different kinds of crabs

本研究的目的是探讨日本宫崎县北川河中日本代龙的保护措施。为了获得制定保护措施的基础数据，对该蟹进行了长期的野外数量调查，实验室对该蟹进行了从产卵到幼鱼的生长试验，通过zoea和megalopa进行了基因分析，鉴定了该蟹在野外的种类，对河床粒度分布进行了偏好试验，并应用生境评价程序对生境的适宜性进行了评价。作为研究成果的保护措施如下：1)沉积物的粒径应在毫米至12mm左右，这与河流中盐楔顶缘沿横向方向的蟹壳成虫尺寸相对应；2)河流结构和/或河流形态应能保持沉积物在洪水点的尺寸分布。

The purpose of this study is to consider measures to preserve Deiratonotus japonicus in the River Kitagawa, Miyazaki Prefecture, Japan. To obtain fundamental data to figure out measures for the preservation of the crab, a long term field survey on its existing number, its growing tests in laboratories from spawn to juvenile through zoea and megalopa, gene analysis to identify the kind of Deiratonotus japonicus in the field, and preference tests on the particle size distribution of river bed as well as application of the habitat evaluation procedure to estimate suitability of habitats. The preservation measure as a research result is the following ; 1)the particle diameter of sediments should range from a scale of millimeter to about 12mm which corresponds to the adult dimension of the crab carapace along the transverse direction at the top edge of salt wedge in the river and 2)river structures and/or morphology of the river should be provided which can keep the size distribution of sediments at the point on flooding.