Habitat preference rather than predation risk determines the distribution patterns of filefish Rudarius ercodes in and around seagrass habitats

Using field and laboratory experiments, this study examined the mechanisms that determine the distribution patterns of the filefish Rudarius ercodes, one of the most dominant seagrass habitat fishes in temperate Japan. Few individuals were preyed on in a field tethering experiment, suggesting a relatively low predation risk, even in the open bare sand and mud areas around seagrass habitats. In the laboratory, predator presence or absence did not affect filefish distribution, with filefish mostly staying in the area planted with seagrass, even when predators were absent in the open bare area. Filefish showed a strong preference for the structure provided by seagrass, staying significantly longer in the seagrass area (despite a lack of food) than in the area with food but devoid of seagrass. Faced with the choice of both seagrass and food, and seagrass without food, even satiated filefish, which showed lower foraging activity, remained significantly longer in the seagrass area with food, suggesting an additional preference for seagrass with abundant epiphytic food. Accordingly, habitat preference may be the most important factor determining the distribution patterns of filefish, which may primarily select seagrass habitats via an intrinsic preference for the structure provided by seagrass, with their distribution pattern subsequently being modified by food availability via a preference for seagrass with abundant epiphytic food.