Intertidal territoriality and time-budget of the surgeonfish, Acanthurus lineatus, in American Samoa

Synopsis

The herbivorous surgeonfish Acanthurus lineatus aggressively maintained feeding territories in the surf zone of the outer reef flat in American Samoa. Intertidal territories were re-established each morning, as well as after displacement by low tides or rough surf. Day-to-day site fidelity of recognizable individuals was high: 99.9% return rate per day for adults (15–20 cm), 99.6% for juveniles (8–13 cm), and 97.2% for recruits (2.5–5 cm). Fish fed on turf algae primarily in the afternoon (80% of available time), and spent 10% of their time on active territorial defense and 2–13% of their time on forays from their territory. On average, a fish defended its territory 1900 times daily and took 17 000 bites (= 7400 bites m⁻² d⁻¹), but rough surf reduced feeding by 60% and defense by 75%. High territorial defense requirements significantly reduced feeding rates. Although the distribution and behavior of this species in Samoa was in large part similar to that reported for it elsewhere (Australia, Indian Ocean), there were notable differences: in Samoa A. lineatus densities within colonies were greater (0.4 fish m⁻²), territory size was smaller (2.3 m²), and defense rate against intruders was greater (2.5 attacks min⁻¹). These differences in Samoa may be related to their smaller body size, greater abundance or increased food supply caused by hurricane damage to reefs which has enhanced the algal turfs that A. lineatus feeds upon.