The Ecological Importance of Parrotfish as Bioeroders and Sediment Producers and Their Conservation Within Small Marine Protected Areas

Parrotfishes can be significant bioeroders and sediment producers on coral reefs but little has been done to quantify this in Hawaii. Scarus rubroviolaceus (scraper) and Chlorurus perspicillatus (excavator) of two different feeding modes were examined. The main determinant of bioeorsion rates was size feeding modes had no significant effect. Bioerosion rates increase exponentially with size, with the largest individuals (45--54 cm fork length (FL)) bioeroding up to 380 +/- 67 kg.indiv-1.yr-1. Parrotfish bioerosion rates in the 41 ha Marine Protected Area (MPA), Hanauma Bay, Oahu, are 4--9 times urchin bioerosion rates on all the examined reef zones and exceed the carbonate accretion on the reef flat. Over 70% of parrotfish bioerosion is by large individuals (>45 cm FL) of one species, S. rubroviolaceus . The overall parrotfish sediment production rate in Hanauma Bay (1.36 kg.m-2.yr-1) exceeds the total sediment production rate in neighboring Kailua Bay (0 9 kg.m-2.yr -1 where parrotfishes are reportedly absent. Large parrotfish species are potentially important bioeroders and sediment producers on reefs in Hawaii. Large parrotfishes are frequently harvested recreationally and commercially in Hawaii. The usefulness of small MPAs in protecting these ecologically important species was investigated. S. rubroviolaceus individuals have small daily home ranges (396--1566 m2) that fit well within the boundaries of Hanauma Bay. They also have high site fidelity, being present in the home range more than 98% of the days monitored. However, S. rubroviolaceus leaves the boundaries of Hanauma Bay in the early morning, probably to aggregate and spawn in deeper waters. Terminal phase males are the most vulnerable to exploitation, as they leave the bay daily almost year round and spend 7--11% of their 24-hr day beyond the reserve boundary. Initial phase individuals are less vulnerable, being absent fewer days of the year and spending only 3--7% of their day beyond the reserve boundary. MPAs should have boundaries that extend beyond the immediate reef to protect the deeper spawning sites. Since larger parrotfishes (>45 cm FL) are the most significant bioeroders and sediment producers, the harvesting of these individuals should also be restricted.