Impact of ocean acidification on montipora capitata growth

In Kāne’ohe Bay Hawai’i, the second most dominant coral species, Montipora capitata is an ecologically important reef building coral that has shown to be resilient to environmental changes. However, ocean acidification may compromise the structural integrity of the coral’s skeleton threatening the species’ resiliency. Therefore, this project will analyze various biological response variables of M. capitata under the stress of ocean acidification (OA). OA is a change in ocean water chemistry due to an increase in atmospheric carbon absorption, which decreases the pH and aragonite saturation state. This also increases the amount 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 aragonite saturation state negatively 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 3 experimental treatments varying in pH and total alkalinity levels, over a month-long experiment. Following experimentation, individual biological response variables from each coral will be measured. These variables include the concentrations of chlorophyll and symbiodinium, along with the protein content and changes in the skeletal density of the coral host. It is hypothesized that the combination of low pH and total alkalinity will have a synergistic effect on the coral’s skeletal density. However, the symbiodinium and chlorophyll will experience an antagonistic effect from the changes in water chemistry. The result of this work aims to determine the driving forces behind the dissolution of coral skeletons under OA conditions in order to support the Proton Flux Hypothesis.