Coral loss and fish guild stability on a Caribbean coral reef: 1974-2000

Data on reef substrate composition and fish guild structure was extracted from filmed underwater surveys conducted in 1974 and 2000 at a coral reef in the Florida Keys. During the course of this 26-year interval the reef underwent a dramatic (> 75 %) loss of stony coral cover, particularly acroporids, accompanied by significant increases in turf algae, crustose-coralline algae, octocorals, and macroalgae. At the same time, marked changes occurred in the structure of a guild of large herbivorous reef fishes. Total abundance declined, and the relative abundance of constituent species and functional groups changed as well. In contrast, we recorded no change in any measure of structural stability in either of two carnivorous fish guilds (lutjanids, haemulids) that feed by night in off-reef habitats. These results are generally consistent with the hypothesis that coral loss differentially impacts functionally dissimilar groups of fishes, according to dependency on reef substrates for food and/or shelter. The persistence of sizeable herbivore populations along with the relatively low (< 16 %) macroalgal cover seen in 2000 suggests that coral loss at our study site was most likely due to bleaching and disease, rather than a response to macroalgal overgrowth. This study represents the first (and only) known study that simultaneously quantifies both a phase-shift in reef substrate as well as concurrent changes in the structure of a reef fish assemblage at a single coral reef in the tropical western Atlantic region.