Meeting Abstract
Caribbean coral reefs have drastically changed over the past 30 years with declines in coral cover and herbivore abundance. In order to regulate increasing competitive macroalgae, protecting the remaining reef herbivores has become a primary conservation goal throughout the Caribbean. However, this assumes that corals are limited primarily by the top-down indirect effect of herbivores on macroalgae. To test the predictions of this herbivore cascade hypothesis along with alternative bottom-up hypotheses, we surveyed the reef community structure (parrotfish abundance and substrate cover) of 34 reefs in the middle region of the Florida Keys National Marine Sanctuary. Reef physical structure was estimated by the first principle component composite variable (distance from shore, depth, visibility, substrate complexity). We estimated the major influences on percent coral cover using both multiple regression analysis and structural equation modelling. Both methods suggest that there are positive top-down (parrotfish), negative bottom-up (reef structure) and negative competitive (fleshy algae) influences on coral. However, the structural equation models suggest that these are not driven by strong negative interactions of parrotfish on turf or fleshy algae. Analysis of parrotfish foraging behavior suggests that diet composition is highly variable and preferences for algae change with relative abundance. These results suggest that hard corals of the middle Florida Keys may be regulated by a complex interaction of top-down and bottom-up influences independent of parrotfish herbivory.
