Production of Dissolved and Particulate Organic Matter by the Reef-building Corals Porites cylindrica and Acropora pulchra

Coral colonies are one of the major producers of dissolved and particulate organic matter (DOM and POM, respectively) in coral reefs. To investigate the net release rates of DOM and POM and the production ratios (DOM:POM), the reef-building corals Porites cylindrica (Dana, 1846) and Acropora pulchra (Brook, 1891) were incubated separately and accumulation rates of DOM and POM in the overlaying seawater were simultaneously measured over 4 d. Release rates of the newly synthesized organic matter by symbiotic algal photosynthesis were also measured using a ¹³C-labeling technique. Dissolved organic carbon (DOC) was produced at rates of 340 and 380 nmol C cm^–2 d^–1 for P. cylindrica and A. pulchra, respectively, and particulate organic carbon (POC) was produced at 590 and 740 nmol C cm^–2 d^–1, respectively. POC was produced at a significantly higher rate than DOC for both coral species: the average ratios were 0.6 and 0.5 for P. cylindrica and A. pulchra, respectively. Particulate organic nitrogen was also produced at a significantly higher rate than dissolved organic nitrogen. These results indicate that reef-building corals produce more POM than DOM at least over the time scale of a few days. Newly-synthesized organic carbon accounted for < 10% of the accumulated bulk DOC, suggesting that most of the released DOC was derived from previously-synthesized organic carbon.