Effects of changes in leaf height and shoot density on the abundance of two fishes,Rudarius ercodes andAcentrogobius pflaumii, in azostera bed

The effects of changes in the structural complexity of a seagrass habitat on the densities of filefish (Rudarius ercodes) and streaked gobies (Acentrogobius pflaumii), were investigated by conducting a 9 month field experiment in aZostera marina bed at Moroiso Bay, Aburatsubo, central Japan. The experimental 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 shoots, but this tendency was not observed during the period of low density. Filefish 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 experimental quadrats, although the species seldom appeared over the surrounding sandy substratum. The results suggested that filefish, unlike gobies, were attracted to factors associated with theZostera leaves, such as epiphytic prey and/or the complex living space.