Spongivory by parrotfish in Florida mangrove and reef habitats

Although parrotfish are generally reported to be herbivorous, increasing evidence suggests that some Caribbean species feed on sponges. After observing grazing scars on the barrel sponge, Xestospongia muta, 40 sponges were videotaped on three reefs for >0.5h to determine the frequency of parrotfish bites on this species. A total of 10h of video recording captured 45 bites on normally coloured X. muta and 527 bites on four bleached X. muta by the parrotfish Sparisoma aurofrenatum, Scarus croicensis and Scarus taeniopterus. The viscera (gut and liver) of 55 parrotfish collected from mangrove and reef habitats were digested in nitric acid and analysed for spicule content. The parrotfish collected in the mangroves (mostly Scarus guacamaia and Sparisoma chrysopterum) had significantly higher masses of spicules in their viscera than did parrotfish collected on the reef (Sparisoma aurofrenatum, Sparisoma viride, Sparisoma chrysopterum, Scarus vetula, Scarus coelestinus and Scarus taeniopterus). The spicules of Geodia gibberosa, a chemically undefended sponge that is common in the mangroves but rare in exposed locations on the reef, were abundant in the viscera of parrotfish collected in the mangroves. These results provide further evidence that fish predation has an important effect on the distribution and abundance of Caribbean sponges.