Photographic technique for the study of coral morphometrics

Abstract

Photographic imagery offers the study of coral morphometrics four principal advantages: speed of sampling, non-destructiveness, an instant permanent record and the opportunity for repeat studies of the same polyps and colony. In this paper, these advantages are weighed against the reduced number of polyp characters that can be accurately measured and the limited number of corals to which the technique is applicable. We were able to measure eight coral traits from images of Favia speciosa, a coral with large circular polyps. Taking readings from slides projected onto paper at 10x actual size proved to be more effective than using computer based image analysis. Corals with small or poorly defined polyps, such as most branching, foliaceous, columnar and laminar species, are not suitable for this approach. The speed of sampling equates to less time in the field, and as the technique is non-destructive, sample size is limited only by the number of colonies present at a site. The technique can identify intraspecific morphological variation in corals with well-defined polyps and could be used, for example, for research into phenotypic plasticity.