本研究探討四草鹽沼濕地之秋季，因鹽度改變而引起之優勢種底藻之變化，以及底藻與優勢小型腹足類－流紋綣(Thiara riqueti)之相關性。結果顯示：小型腹足類－流紋綣之幼生，在秋季10月間會大量出現於三百多公傾之四大研究樣區間，且混生於絲藻(Ulothrix sp.)族群中，此時期之樣區鹽度因雨季過後皆低於1.0%，絲藻族群成為低鹽度之四大樣區之主要優勢種。然而，經光學顯微鏡鏡檢結果，發現混生於優勢種絲藻族群中流紋綣幼生之尾部尖端，皆緊密的連著萌芽中之綠藻－腸滸苔(Enteromorpha intestinalis )的幼苗，而非絲藻族群。當鹽度增至3.0%後，樣區內之絲藻群體多已漸褪色與死亡，腸滸苔則漸成優勢。此結果顯示樣區內之優勢種底藻的季節性消長不僅受鹽度改變之影響外，亦有植食腹足類參與營養源及著生基質之提供，且消長過程在當年之秋季僅歷經短短三週。 This study focused on the succession of dominant benthic algae due to the variation of water salinity, and on the relationship between the benthic algae and the gastropods Thiara riqueti in autumn at Szu-Tsao wetland. The larvae gastropods T. riqueti were found abundantly in the four studying areas during October, and grew around a population of Ulothrix sp. After the raining season, the water salinity was lower than 1.0%, resulting in dominant growth of Ulothrix sp. in the areas. However, a green algal species of Enteromorpha intestinalis, not the Ulothrix sp. was found attaching the posterior of larvae gastropods under light microscope observation. Moreover, when the water salinity increased to 3.0 %, the Ulothrix sp. population became dead and colorless, and E. Intestinalis turned to be dominant gradually. The results show that the seasonal variation of dominant benthic algae was controlled not only by water salinity but also by the population of herbivorous gastropod which could provide the nutrients and substrates for algal growth. The seasonal succession of dominant benthic algae during autumn occurred within only three weeks.