Tissue condition and growth rate of corals associated with schooling fish1

Juvenile french and white grunts ( Haemulon flavolineatum and Haemulon plumieri ) form diurnal resting schools over colonies of Porites furcata and Acropora palmata in St. Croix. We studied the effect of these grunts on the tissue composition and growth rate of corals, Porites furcata colonies with grunts had significantly more tissue cm −2 , N cm −2 and zooxanthellae cm− 2 than colonies without grunts. Acropora palmata colonies with grunts also showed elevated amounts of N cm −2 and P cm −2 . Seasonal changes were also observed in these parameters and in coral growth rates and skeletal density, apparently related to light availability. Several measures of coral growth rate were significantly greater in P. furcata colonies with grunts. Grunts were removed from two colonies, and growth rates before and after removal were compared to rates in reference colonies. Before removal most growth rate measures were greater in the colonies with grunts; after removal growth rates were lower or not significantly different. These data demonstrate that schools of resident fishes can stimulate coral growth, perhaps by providing nitrogen supplements.