INCREASES IN SURGEONFISH POPULATIONS AFTER MASS MORTALITY OF THE SEA-URCHIN DIADEMA-ANTILLARUM IN PANAMA INDICATE FOOD LIMITATION

In 1983/1984, Diadema antillarum suffered mass mortalities throughout its West Atlantic range. Its populations were reduced by 95% and subsequently have failed to recover. These die-offs led to sustained increases in the abundance of soft algae, including types eaten by herbivorous reef fishes. I monitored adult populations of three herbivorous surgeonfishes (Acanthurus coeruleus, A. chirurugus and A. bahianus) between 1978 and 1990, and the recruitment of their pelagic juveniles between 1979 and 1989, on six patch reefs in Panama. Adult populations of A. coeruleus and A. chirurgus, which largely restrict their feeding to reef substrata, increased by averages of 250 and 160%, respectively, after the die-off of D. antillarum in 1983. No increases occurred in the adult populations of A. bahianus, which often feeds in off-reef habitats unaffected by D. antillarum. Average annual levels of juvenile recruitment of all three surgeonfishes did not differ before and after the die-off. These results support the hypothesis that adult populations of two herbivorous fishes that are strongly reliant on reef algae for food previously were limited by competition with D. antillarum.