Three-dimensional morphometric measurements of reef corals using underwater photogrammetry techniques

We describe a novel technical approach to accurately measure surface area a nd other morphological characteristics of corals and similar irregular obje cts from underwater photography. A standard Nikonos camera system was used with a slide-scanner to produce multiple overlapping images of the object. Photo-Modeler software was used to process the images and build a 3-D model of the object, which was subsequently analyzed using 3-D computer-aided de sign (CAD) packages. The accuracy of the technique was tested on irregularl y shaped polystyrene models of known dimensions and on preserved coral skel etons. The technique was applied to the quantitative assessment of partial mortality in corals, but many applications are possible, including surface area measurements to standardize ecophysiological studies in the field and morphometric analyses. It represents the only noninvasive technique we are aware of for determining surface areas of large corals in the field. The mo st serious limitation of the technique is the time-consuming nature of the process, which increases with the complexity of the object and precludes ma ny routine applications.