Impact of ocean acidification on Montipora capitata

In Kāne‘ohe Bay Hawai‘i, the second most dominant coral species, Montipora capitata is an ecologically important reef-building coral that has shown resilience to environmental changes. However, ocean acidification (OA) may compromise the structural integrity of the coral's skeleton, threatening the species’ resiliency. Therefore, this project analyzed multiple biological response variables of M. capitata under ocean acidification conditions. OA is a change in ocean water chemistry due to an increase in the absorption of atmospheric carbon, which decreases seawater pH and aragonite saturation state. This also increases the concentration of hydrogen ions in the water, which will impact the total alkalinity, or the ability of the water to neutralize ions. Previous research has stated that a lower concentration of carbonate impacts the coral’s ability to calcify under OA conditions. Contrarily, the Proton Flux Hypothesis states that the increase in hydrogen ions limits coral calcification under OA. To better understand coral growth under OA conditions, corals were exposed to a control and three experimental treatments varying in pH and total alkalinity levels, over a month-long experiment. Following experimentation, biological response variables from each coral were measured. These variables include the density and chlorophyll concentrations of the symbiotic algae and changes in skeletal density. It is hypothesized that the combination of low pH and total alkalinity will have a synergistic effect on the coral's skeletal density. The result of this work aims to further our understanding of OA and its impacts on coral calcification.