The productivity of San Cristobal Reef, Puerto Rico

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 equation y = 0.58x – 0.18, where y = g O₂·m^–2 reef area·h^­–1 and x = mEin·m^–2·s^–1, describes the correlation between light and metabolism at this site. Net primary productivity was 2.45 g O₂·m^–2 reef area and gross primary productivity 5.42. The ratio of gross primary productivity to 24-h respiration was 0.7. Productivity rates of this heterotrophic zone are lower than those reported for shallower reef zones with greater algal cover.