San Cristobal Reef, Puerto Rico, was the site of a community metabolism study based on a new upstream-downstream method with experimental channels 4 m deep. Net productivity rates varied from 0.03 to 1.85 g O2m–2 reef area·h–1 (x = 0.39; n = 59). Respiration measurements of one reef section from which light was excluded ranged from 0.26 to 0.48 g O2·m–2 reef area·h–1. The linear regression equati