Habitat selection in the juvenile manini

Typescript.Bibliography: leaves 120-125.viii, 125 l illus., tablesThe mechanisms of habitat selection are investigated for the juvenile stage of a common Hawaiian reef fish, the manini. Two questions are posed. First, to which environmental stimuli does the juvenile manini respond in making its choice of habitat? Second, what behavioral mechanisms mediate the complex choices involved in habitat selection? The late larval stage moves from the pelagic to the inshore environment. Analyses of distribution of post-transformation juveniles show, however, that these fish continue to select habitats once in the inshore environment. The type of habitat selected 'slowly changes, with respect to depth of water, as the fish grow. Field data also show distribution to be correlated with presence of substratum, cover, and algal food. Color and texture of substratum, presence of other fish, and amount of water movement seem of lesser importance. Temperature, salinity, and oxygen concentration do not vary in a manner which would permit their use as habitat selection stimuli. Laboratory experiments were designed to investigate the importance of substratum character, cover, food, water depth, light intensity and direction, degree of water movement, and presence of other juvenile manini as stimuli. Juvenile manini orient strongly toward a substratum. On this substratum availability of cover and food are prime requirements. Water depth is of lesser importance. Manini do select for water depth in accordance with their field distribution, but only if cover is present. Degree of water movement and presence of other manini are of secondary importance for habitat selection. Light intensity and direction, and substratum color and texture are of little if any importance as habitat seleotion stimuli. A hypothesis is presented relating intensity (= frequency) of exploratory behavior to stimulus feedback from the immediate environment. It is proposed that habitat selection occurs because animals in a "poor" environment show high levels ,of exploratory behavior while animals in a "good" environment show reduced levels of exploration. This obviates the necessity of postulating "knowledge" of what constitutes a suitable environment. It is further predicted that when exploration level is high, time available for non-exploratory behaviors is reduced. Thus levels of these behaviors are highest in the better environments. This hypothesis is tested by using the previously determined responses of manini to variation in depth and cover. Four test environments of known relative habitat suitability are utilized. Behavior in these four environments is as predicted by the hypothesis. Habitat selection in manini is discussed relative to other examples of complex choice behavior. The hypothesis accounts for more aspects of habitat selection behavior than do other previously proposed hypotheses