When resources are economically defendable, interspecific aggression may oc
cur when one species attempts to use the defended resources to the detrimen
t of the defending species. In the Florida Keys, we investigated vigorous a
nd frequently observed aggression between the Redband Parrotfish, Sparisoma
aurofrenatum, and the Redtail Parrotfish, Sparisoma chrysopterum, along wi
th microhabitat overlap and foraging overlap. Sparisoma chrysopterum home r
anges extensively overlap S. aurofrenatum territories. Both parrotfishes ar
e found over and feed upon Halimeda opuntia, a green calcareous alg a, sign
ificantly more than all other microhabitats. Interspecific aggression by th
ese parrotfishes is primarily directed toward confamilials. Extensive overl
ap in distributions combined with overlap in microhabitat and foraging beha
vior likely play a role in fostering the disproportionately high interspeci
fic aggression observed between these two parrotfishes in the Florida Keys.