Exploring the interactive effects of light intensity and pH on coral oxygen production

Abstract

The study aimed to explore the possible interaction between acidification and light intensity and the effects on corals' oxygen production. Interactions between temperature and pH have been thoroughly researched and proven to cause immense stress on the world’s reefs. We hypothesize that increased CO2 concentration from acidification, combined with higher light intensity, could benefit the photosynthetic zooxanthellae and lead to higher oxygen production. For this study, two species of tropical coral were used (Montipora capricornis and Seriatopora caliendrum). First, the corals were placed under five different light intensities (200, 400, 600, 800, and 1000 PAR) to determine the optimal light level (highest oxygen production) and harmful light intensity (lowest production). Afterward, different levels of acidification were tested; a pH of 7.6 (most acidic) pH 7.8, and 8.2. Results from a one-factor ANOVA showed that for M. capricornis oxygen production was at its highest at a light intensity of 600 PAR (mean oxygen production was 0.000697 ppm O2 /area coral in mm2), and 800 PAR was considered harmful (mean oxygen production was 0.000397 ppm O2 / mm2). For S. caliendrum optimal light intensity was 400 PAR (0.379 ppm O2/gram) and lowest at 1000 PAR (0.0725 ppm O2/gram). A two-factor ANOVA showed that pH and the interaction between pH and light intensity were significant. For M. capricornis, O2 production was the highest in pH 8.2 in optimal light, and in harmful light oxygen production increased as acidification increased. For S. caliendrum, O2 was overall highest under acidic conditions (pH 7.6). The results give support that there is an interaction between light intensity and pH.