Abstract
The Ariake Sea has a large tidal range, and therefore, large amounts of suspended solids are transported to the river. The growth and expansion into tidal riverbank of Phragmites australis depends on the sedimentation of mud solids on the riverbank, and the large expansion of P. australis can cause floods. We had proposed the construction of trenches on riverbanks to control the expansion of P. australis; however, their impact on the habitat of aquatic organisms was unclear. The objectives of this study were to provide insights into the aquatic fauna in the trenches and to discuss the association between aquatic fauna and 4 structurally different types of trenches on the banks of the Ushizu River in Saga, Japan. We studied the population of aquatic organisms in each trench using the D-flame net. Shrimps (Exopalaemon holthuis) were predominantly found in all trenches in the summer and autumn seasons. The predominance of goby, Tridentiger bifasciatus, increased in the summer. It was suggested that this results depend on the introduced juvenile of T. bifasciatus into these trenches from river; because it was shown that the result of standard length (SL). While these trends did not depend on the structure of the trenches, our results suggested that specific species, namely Periophthalmus modestus and Cleistostoma dilatatum, prefer shallow trenches as tidal flats. Moreover, we collected more endangered species, Oryzias latipes, and aquatic insects from all the trenches than from the neighboring riverside, suggesting that these trenches have provided a habitat for rare fish and aquatic insects.
