PHOTOGRAPHIC VERSUS VISUAL CENSUS TECHNIQUES FOR THE QUANTIFICATION OF JUVENILE CORALS

The abundance of juvenile corals was quantified by visual and photogra phic methods to determine whether photography could be used as a rapid census technique in reef monitoring projects. Between 9 and 17 0.25-m (2) quadrats were positioned randomly along replicate 25-m transects o n reefs in St. John (U.S. Virgin Islands), the Florida Keys, and Beliz e. In the visual method, all juvenile corals (0.4 cm less than or equa l to diameter less than or equal to 5.0 cm) in both open and cryptic l ocations within the quadrats were identified to genus and counted. A c lose-up photograph of a 0.039-m(2) planar area was then taken in the c enter of each quadrat for subsequent analysis. Plots of the running me an and standard error of juvenile density against the number of transe cts produced asymptotes after approximately three transects at each si te, suggesting that sample sizes were sufficient for both methods. How ever, juvenile densities estimated by the visual method were not corre lated with values obtained by the photographic method at any site. The se discrepancies cannot be attributed to dissimilar sampling areas, be cause analysis of variance demonstrated that the difference between me thods varied among sites, and because similar variation was apparent w hen visual and photographic surveys were compared for similar sample a reas. Rather, the discrepancies are a consequence of juvenile corals g rowing in microhabitats where they cannot be quantified in planar phot ographs. We recommend the visual technique to quantify juvenile corals ; at four sites we found that adequate estimates of juvenile density c an be obtained from surveys of 0.5 x 0.5 m quadrats, randomly position ed at 17 locations along each of four 25-m transect lines.