Development of methods of preservation of aquatic environment with probability of extinction

为了保护日本稀有蟹类Deiratonotus damnus，对九州岛北川的蟹类数量变化、栖息地特征和生长过程进行了野外调查和实验室试验。研究结果表明：1）黄粉虫主要分布在距河口4.8 ~ 6.4km的感潮河段，2）黄粉虫数量呈下降趋势，观测期内黄粉虫数量在356 ~ 41万只之间;（3）沙床水槽实验结果表明，对壳长9mm的杜父鱼，最大临界牵引力为1.19Pa;（4）杜父鱼喜栖于河床直径5 ~ 80 mm、水温20 ~ 25℃、盐度0 ~ 10左右的生境;结果表明：1）雌蟹平均孵化出蚤状幼体710只，卵孵化至少需要2个月，蚤状幼体从第1期到第2期需要5天，从第2期到第3期需要9天。

In order to preserve Deiratonotus japonicus, a rare species of crab in Japan, field surveys and laboratory experiments were carried out to investigate factors which influence changes in number, characteristics of the habitat, and the process of growth of Djaponicus in the Kita River, Kyushu island. Based on the results, correlations of each factor and population density of D.japonicus were analyzed.Research results are as follows :1)D.japonicus mainly distributes in a tidal reach from 4.8km to 6.4km from the river mouth ;2)D.japonicus tends to decrease in number, and was in a range of 3,560,000 to 410,000 individuals at the observation period ;3)Experimental results in a flume with sand bed shows 1.19Pa of the maximum critical tractive force for 9mm of D.japonicus in carapace ;4)D.japonicus prefers habitat with 5 to 80mm of riverbed materials in, diameter, 20 to 25℃ of water temperature and near 0 to 10 of salinity ;5)The number of zoeae hatched from one female crab was 710 on an average ;6)it takes at least two months for D.japonicus' eggs to hatch ; and7)It takes 5 days to become the second stage of zoea from the first and 9 days to grow the third from the second.