Importance of differentiating Orbicella reefs from gorgonian plains for ecological assessments of Caribbean reefs

Abstract

Region-wide assessments of coral cover typically rely on meta-analyses of small-scale ecological studies which have combined different coral reef habitats. This is particularly problematic on forereefs where at least 2 habitats can be found; coral-based bioherms and colonized hardgrounds (hereafter Orbicella reefs and gorgonian plains), each with very different structure and scleractinian coral cover. Here, we quantify the degree to which the failure to differentiate forereef zones dominated by framework building corals, mainly Orbicella spp. (hereafter Orbicella reefs) from gorgonian plains can lead to biased assessments of coral cover. We also provide a baseline of an extensive sample of Caribbean coral reefs in 2010-2012 for the 2 habitats within the forereef. Mean scleractinian coral cover (±SE) at Orbicella reefs was 24 ± 1.3%, more than double the coral cover found on the gorgonian plains (10 ± 1.6%). The difference in coral cover between habitats within the same geomorphological zone is consistent with those calculated from an independent dataset for the basin (Atlantic and Gulf Rapid Reef Assessment). Furthermore, the average coral cover calculated for Caribbean Orbicella reefs was more than double the values previously reported for entire reefs in the region a decade ago (10%), which integrated data from different habitats, depths, time periods and surveyors. Differentiating between forereef habitats has provided a meaningful baseline of coral state, which allows for realistic targets for management in the Caribbean basin.