摘要
蘭陽溪流域橫跨全宜蘭縣境內，是蘭陽平原中最重要的一條河川，無論在民生經濟及環境指標上均佔有重要的地位。為對此河川生態有清晰的瞭解，選定在蘭陽溪全河域及其支流冬山河匯入蘭陽溪出海口之樣站，進行蟹類多樣性及空間棲所分布研究。本研究紀錄全河域之蟹類總計7科28種，冬山河匯入蘭陽溪的河口域樣站之蟹類計有4科14種。
在蟹類空間棲所分布的研究上，從三方面測量比對各數據在高低潮位是否有明顯之差異（1）底質：本樣站蘭陽溪河口之底質屬性為砂質土壤，底質變異隨季節與高低潮位影響不大，（2）蟹類共域：本樣站日間優勢種為2科5種：弧邊招潮蟹（Uca arcuata）、北方招潮蟹（Uca borealis）、清白招潮蟹（Uca lactea）、角眼拜佛蟹（Tmethypocoelis ceratophora）及台灣厚蟹（Helice formosensis）；夜間優勢種為1科2種：無齒螳臂蟹（Chiromantes dehaani) 、紅螯螳臂蟹（Chiromantes haematocheir)。且高低潮位之優勢種蟹類呈現不同共域分布情形，顯示高低潮位有不同種的共域情形，且高潮位之共域情形較多樣性，（3）洞穴：於每單元中計算高低潮位之洞數，結果呈現低潮位之洞徑小、數量多及密度高之情形。
綜上潮位與種類分布之關係密切，與前人提出研究假說相符。
本研究更分析3種優勢種蟹類：弧邊招潮蟹（U. arcuata）、北方招潮蟹（U. borealis）、清白招潮蟹（U. lactea），其雄蟹大螯的左右性，發現大螯與進出洞呈正相關。
希望本研究結果之發現能對未來有關河口蟹類的生態研究上提供微薄貢獻。

ABSTRACT
The Lan-Yang River System occupies the whole Yi-Lan County, and the main river, Lan-Yang River, plays the significant role of the indicators of economy and environment in Lan-Yang plain. Yi-Lan River and Dong-Shan River join the River System by connecting with the mouth region of Lan-Yang River to develop an unique estuarine ecosystem.

In order to get more ecological information, the crab diversity survey was conducted from up-stream to down-stream of the Lan-Yang River; and the crab diversity and habitation in the tidal flat where the Dong-Shan River connected Lan-Yang River was set a site to study.

A total of seven families and twenty-eight species of crabs are found from the up-stream to down-stream of the Lan-Yang River; and four families and fourteen species in the tidal flat of the study site of the Dong-Shan River and Lan-Yang River connected area.

In the study of the habitation of crab community in the study site, data of three aspects has been collected during the high and low tide conditions and has been analyzed.
1. The material of substrate: samples analysis indicates that the substrate material is sand loam and doesn’t show much influence on seasonal changes and the tidal conditions.
2. Crabs sympatric relationship: the data confirms that five species: Uca arcuata, Uca borealis, Uca lactea, Tmethypocoelis ceratophora and Helice formosensis are dominant in daytime; two species: Chiromantes dehaani and Chiromantes haematocheir dominate in nighttime. In addition, it appears the different sympatric combinations in the high and low tide zones. And there is more diversity in the high tide zone.
3.The burrows：burrows in low tide zone are small, more in numbers and high density.
Overall, this study shows that the crab species distribution and the tidal conditions has close relationship, and this corresponds with hypothesis from predecessors.

The handedness of three dominant species of Fiddler Crabs: U. arcuata, U. borealis and U. lactea has been recorded. And the research shows that there is positive correlation of the side of major chela and burrow-emerging-entering.

Hope this study can provide a basis of ecological information of crabs for the further understanding about Lan-Yang River Ecology.

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