Effects of changes in leaf height and shoot density on the abundance of two fishes, Rudarius ercodes and Acentrogobius pflaumii, in a Zostera bed

The effects of changes in the structural complexity of a seagrass habitat o n the densities of filefish (Rudarius ercodes) and streaked gobies (Acentro gobius pflaumii), were investigated by conducting a 9 month field experimen t in a Zostera marina bed at Moroiso Bay, Aburatsubo, central Japan. The ex perimental design included a control and 7 treatments where leaf height or shoot densities were reduced. During the period of high density of filefish , the species was more abundant in quadrats with longer leaves and denser s hoots, but this tendency was not observed during the period of low density. File-fish did not frequent the quadrat cleared of seagrass or the area of sandy substratum surrounding the experimental seagrass bed at any time. The abundance of streaked gobies did not differ significantly among 8 experime ntal quadrats, although the species seldom appeared over the surrounding sa ndy substratum. The results suggested that filefish, unlike gobies, were at tracted to factors associated with the Zoster a leaves, such as epiphytic p rey and/or the complex living space.