The 1971 red tide and its impact on certain reef communities in the mid-eastern Gulf of Mexico.

Effects of the 1971 spring-summer red tide upon mid-eastern Gulf of Mexico patch reef communities are discussed. In situ (SCUBA) observations at widely scattered reef localities between 13-30 m off Sarasota, Florida, both before and after the red tide support the following: 1) under the appropriate environmental conditions, red tides may result in near-complete extirpations of shallow-water (less than 40 m) reef biotas from extensive areas on the inner central-West Florida Shelf), 2) recolonization by certain biotic groups is relatively rapid (e.g., benthic algae and fishes) while that of others (e.g., alcyonarian corals, scleractinian corals, and echinoderms) is slow and may require several years, and 3) seasonal progression as well as true ecological succession following certain red tides may temporarily result in floral and faunal assemblages qualitatively and quantitatively distinctive from those prior to the red tide. It is therefore suggested that certain red tides, particularly those generated beneath pronounced thermoclines, may be previously underestimated phenomena regulating the composition, abundance, and distribution of shallow-water reef biotas in the mid-eastern Gulf of Mexico. It is surmised that the periodic occurrence of these red tides may prevent the evolution of a climax or equilibrium reef community.