Grazing Effect on Sea Grasses by Herbivorous Reef Fishes in the West Indies

Abstract

A conspicuous band of bare sand averaging about 30 ft in width often separates reefs and beds of sea grasses (Thalassia and Cymodocea) in the Virgin Islands and other islands of the West Indies. This zone of sand appears to be the result of heavy grazing by parrotfishes (Scarus and Sparisoma) and surgeonfishes (Acanthurus) that stay close to reefs for shelter from predaceous fishes. Floating sea grass fragments are eaten by the halfbreak Hemiramphus brasiliensis and occasionally by the Bermuda chub Kyphosus sectatrix and the triggerfish Melichthys radula. Within the beds, the sea grasses are fed upon by the small resident parrotfish Sparisoma radians, the echinoids Lytechinus, Tripneustes, and Diadema, the green turtle Chelonia mydas, and in part by the queen conch Strombus gigas, and manatee Trichechus manatus. It is the author's opinion that if the pre—Columbian population of the green turtle could be restored and its fishery properly regulated, the enormous production of the sea grasses in the Caribbean region could be realized more fully for the benefit of man.