Nutrient pollution disrupts key ecosystem functions on coral reefs

There is a long history of examining the impacts of nutrient pollution and pH on coral reefs. However, little is known about how these two stressors interact and influence coral reef ecosystem functioning. Using a six-week nutrient addition experiment, we measured the impact of elevated nitrate (NO3) and phosphate (PO43) on net community calcification (NCC) and net community production (NCP) rates of individual taxa and combined reef communities. Our study had four major outcomes: 1) NCC rates declined in response to nutrient addition in all substrate types; 2) the mixed community switched from net calcification to net dissolution under medium and high nutrient conditions; 3) nutrients augmented pH variability through modified photosynthesis and respiration rates; and 4) nutrients disrupted the relationship between NCC and aragonite saturation state documented in ambient conditions. These results indicate that the negative effect of NO3 and PO43 addition on reef calcification is likely ...