河川生態體系中，生物的分佈、相對數量及生物群聚組成，往往決定於水生生物之棲地結構特性，造成棲地的多變性以水流為最。水流對於水生生物的影響甚巨，本次調查以石門鄉之溪流－老梅溪為對象，從河口起共設立5個測站，觀察水流流速對腹足類動物川蜷 ( Semisulcopira libertine ) 以及瘤蜷 ( Thiara granifera ) 族群影響。
水流對川蜷的平均體長及標準機差 ( SE ) 有相關性。瘤蜷與川蜷分別分佈在老梅溪的河口下游與中上游區，二種螺類種間表現強烈的棲地選擇性。流速影響川蜷族群組成結構，且也限制其遷移能力，而影響其分佈，但瘤蜷分佈不受流速影響。在溪流中，瘤蜷與川蜷的分佈及型態的變化由趨流性所影響。不同的流速顯示不同成長模式及不同殼型的表現型。
Current velocity strongly influences habitat diversity in stream. We investigated the effect of current velocity on the distribution of Semisulcopira libertina and Tarebia granifera at five stations on the Lau Mei Stream in Shin - Men County, Taiwan. T. granifera was more abundant at stations with lower current velocity, whereas S. libertin predominated at higher velocity stations. No significant difference was found in average shell length and shape of T. granifera among sataions, but S. libertin did exhibit significant inter- station differences in these parameters. Current velocity appears to affect shell length in S. libertin but not in T. granifera , and the two species’ disjunct distribution between upstream and downstream may be a result of intense interspecific competition. Current veolocity appears to affect structure and migration of S. libertin but not of T. granifera . Migrations and distribution of both S. libertin and T. granifera appear to be influenced by rheotaxis, geotaxis, and current velocity.
