Scale dependent spatial variability of corral assemblages along the Florida Reef Tract

Coral reef communities of the western Atlantic have changed over the past t wo to three decades, but the magnitude and causes of this change remain con troversial, Part of the problem is that small-scale patterns observed on in dividual reefs have been erroneously extrapolated to landscape and geograph ic scales. Understanding how reef coral assemblages vary through space is a n essential prerequisite to devising sampling strategies to track the dynam ics of coral reefs through, time. In this paper we quantify variation in th e cover-of hard corals in spur-and-groove habitats (13-19 m depth) at spati al 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 scale s: (1) among transects within sites (0.01- to 0.1-km scale), (2) among site s 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 (5 0- 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 characte rize nearby reefs, nor did those estimates sufficiently represent variabili ty at the scale of the sector. The structure and composition of coral reef communities is probably determi ned by the interaction of multiple forcing functions operating on a variety of scales. Hierarchical analyses of coral assemblages from other geographi c locations have detected high variability at,scales different from those i n the present study. A multiscale analysis should, therefore, precede any m anagement decisions regarding large reef systems such as the Florida Reef T ract.