曾文溪口台灣招潮棲地特性研究

Habitat of Uca formosensis in the Zengwen Estuary of Southwestern Taiwan

台灣招潮為台灣原生招潮中唯一的特有種，近十幾年來3個較大的族群數量已驟減。本研究針對1992-1994年及2008-2010年調查結果，進行曾文溪口地區底棲蟹類群聚分析，探討台灣招潮分布範圍、棲地特性及曾文溪口地區環境變遷等。1992-1994年調查設置由4個50㎝×50㎝正方形小區組成的樣區，挖掘樣區內的底棲蟹類，共取得96個樣區資料，計算各樣區蟹類之重要值指數，群聚分析利用定量資料，採用多變數分析之分類法及分布序列法來計算樣區間蟹種組成之變異，台灣招潮、乳白招潮、弧邊招潮、北方招潮、萬歲大眼蟹、台灣厚蟹與德氏仿厚蟹在分布序列第1軸上分數相當。2008-2010年之調查再依據動態影像及挖掘樣區，確認其出洞活動時機以計算族群數量。為瞭解台灣招潮棲地特性，分別檢測微棲地之pH值、鹽度、電導度、重金屬、土壤粒徑、土壤有機質、水中溶氧量及潮位變化等環境因子資料，台灣招潮主要群聚範圍為高潮線際坡度5°以下之壤土。依據台灣地區土壤重金屬含量標準與等級區分表中，曾文溪口重金屬檢測值多介於第2-3級，但鎘為第4級，毒害級，土壤中有外來重金屬介入，顯示有中度污染之現象。再比較大肚溪口之採樣數據，2008年於大肚溪口南岸之原台灣招潮棲地，其檢測值遠超過第5級，污染程度較曾文溪口高很多。曾文溪口的地形有巨幅變化，新浮崙沙洲南端內縮極為嚴重，原分佈於此之台灣招潮已隨棲地流失而消失，早期台灣招潮原分佈之曾文溪口北岸及主棲地西南區多開發成魚塭。由於自然及人為因素所造成之地形變化，影響水位、土壤特性、鹽度及其對棲地之利用，新開挖的魚塭佔據台灣招潮最適棲地，若無法控管魚塭的擴展，則台灣招潮的族群量難以復原。

Uca formosensis is an endemic fiddler crab to Taiwan. In the past decade, its population has severely decreased. We investigated the crab community and related environmental factors at the Zengwen Estuary in the southwestern Taiwan for the periods of 1992 to1994 and 2008 to 2010. The crabs were sampled with digging method and digital camera at 96 plots, each with 1m^2 area divided into four 50×50㎝^2 subplots. For each plot, the species of the crabs were identified and the number of each of the species were counted and presented as the important value index (IVI). Multivariate statistical analysis, classification and ordination, were used for the quantitative analysis of the crab community variations. The species composition of the community, and population sizes of the species and their distribution patterns, habitat types and topography were examined. Environmental factors such as dissolved oxygen saturation in water, and pH, salinity, electric conductivity, heavy metals, particle-sizes, organic matters of the soil were analyzed. Loam in the upper inter-tidal zone with gentle slopes of less than 5° was found to be the most suitable habitat for the crabs. According to soil heavy metal content standards and classification of Taiwan, the heavy metal contents were at the 2^nd and 3^rd grades, while cadmium was at the 4th grade, indicating an intermediate pollution. At the Dadu Estuary in the central western Taiwan, the heavy metal contents at the dots where U. formosensis were found were over the 5^th grade, 2008. The topography of the estuary has been changed dramatically due to the natural factors and human activities, affecting water level, soil characters, salinity, and habitat utilization of the crabs. The southern region of the New Fuluen Sandbar almost disappeared, while there were many fish ponds that had been constructed in the higher intertidal zone where was once the most suitable habitat of the crabs. This resulted in a serious reduction of the U. formosensis population. The conservation of U. formosensist requires minimization of human disturbances, particularly from construction of fish ponds.