Environmental Futures Seminar - Nancy Prouty

Coral reefs and their ecosystems are threatened by both global stressors, including increasing sea-surface temperatures and ocean acidification (OA), and local stressors such as land-based sources of pollution that can magnify the effects of OA. The shallow coral reefs off Kahekili, West Maui, Hawaii are exposed to nutrient-enriched, low-pH submarine groundwater discharge (SGD) and are particularly vulnerable to the compounding stressors from land-based sources of pollution and lower seawater pH. Rates of coral calcification are substantially decreased, and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the Pacific under equivalent low pH conditions but living in oligotrophic waters. Secondary effects of nutrient-driven increase in phytoplankton biomass and decomposing organic matter contribute to an already compromised carbonate system (i.e., reduced pH and Ωarag), tipping the balance between net carbonate accretion and net carbonate dissolution. However, elevated pH up-regulation suggests that corals exposed to nutrient-enriched, low pH effluent sustain supersaturated calcifying fluids with respect to aragonite, possibly as an internal coping mechanism to combat multiple stressors from land-based sources of pollution.