Effects of elevated pCO sub(2) on epilithic and endolithic metabolism of reef carbonates

摘要

We investigated effects of elevated partial pressure of CO sub(2) (pCO sub(2)) on the metabolism of epilithic and endolithic phototrophic communities that colonized experimental coral blocks. Blocks of the massive coral Porites lobata were exposed to colonization by epilithic and endolithic organisms at an oceanic site in Kaneohe Bay (Hawaii) for 6 months, and then were transported to laboratory tanks. A bubbling system was used to maintain two treatments for 3 months, one at ambient pCO sub(2) (400 ppm) and the second at elevated pCO sub(2) (750 ppm). Net photosynthetic rates of epilithic communities in the high pCO sub(2) treatment, dominated by encrusting coralline algae, decreased by 35% while respiration rates remained constant. In contrast, metabolism of endolithic phototrophs, comprised of cyanobacteria and algae, was not significantly affected by the elevated pCO sub(2) even though endoliths contributed about 63% to block production.