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

本研究旨在探讨日本宫崎县北川河的保护措施。为了获得基础数据，以找出保护措施，长期实地调查其现有数量，在实验室中进行从卵到幼蟹到蚤状幼体和大眼幼体的生长测试，基因分析以确定现场的Deiratonotus rectus的种类，和偏好性试验，以及应用生境评价程序来评价栖息地作为研究成果的保护措施如下：1）沉积物的颗粒直径应在毫米至12毫米左右的范围内，这与河流中盐楔顶部边缘处蟹背沿着横向的成年尺寸相对应; 2）河流结构和/或或河流的形态，它可以保持在洪水点的沉积物的粒度分布。

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.