Scale-dependent spatial variability of coral assemblages along the Florida Reef Tract

Abstract

 Coral reef communities of the western Atlantic have changed over the past two to three decades, but the magnitude and causes of this change remain controversial. Part of the problem is that small-scale patterns observed on individual reefs have been erroneously extrapolated to landscape and geographic scales. Understanding how reef coral assemblages vary through space is an essential prerequisite to devising sampling strategies to track the dynamics of coral reefs through time. In this paper we quantify variation in the cover of hard corals in spur-and-groove habitats (13–19 m depth) at spatial scales spanning five orders of magnitude along the Florida Reef Tract. A videographic sampling program was conducted to estimate variances in coral cover at the following hierarchical levels and corresponding spatial scales: (1) among transects within sites (0.01- to 0.1-km scale), (2) among sites within reefs (0.5- to 2-km scale), (3) among reefs within sectors of the reef tract (10- to 20-km scale), and (4) among sectors of the reef tract (50- to 100-km scale). Coral cover displayed low variability among transects within sites and among sites within reefs. This means that transects from a site adequately represented the variability of the spur-and-groove habitat of the reef as a whole. Variability among reefs within sectors was highly significant, compared with marginally significant variability among sectors. Estimates from an individual reef, therefore, did not adequately characterize nearby reefs, nor did those estimates sufficiently represent variability at the scale of the sector.

The structure and composition of coral reef communities is probably determined by the interaction of multiple forcing functions operating on a variety of scales. Hierarchical analyses of coral assemblages from other geographic locations have detected high variability at scales different from those in the present study. A multiscale analysis should, therefore, precede any management decisions regarding large reef systems such as the Florida Reef Tract.