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Using AquapHOx to Study Growth and Survival of Corals


Corals are one of the most graphic examples of how marine species can be negatively affected by a multitude of anthropogenic stressors. One of these is ocean acidification, which stems from increased levels of atmospheric CO2.

Since the beginning of the Industrial Revolution, the average pH level of Earth’s oceans decreased from 8.2 to 8.1. While on paper this may look small, in the ocean it has a much bigger impact since the relationship between pH and acidity is indirect and logarithmic. pH is a quantitative measurement of acidity in a solution. Each decrease of one pH unit translates to about a ten-fold increase in solution’s acidity. This means that the acidity of today’s oceans is about 25% greater* than what it was compared to preindustrial times. The ocean’s acidity is projected to increase by over 100%** by the end of this century if CO2 emissions caused by humans isn’t reduced.

The biological impacts of the increased acidification will vary depending on the marine organism. However, overall it will impact many of them by compromising their ability to sustain life, reproduce, and recover from disturbances.

In his research, Matteo Bravo from University of Amsterdam investigated how different environmental variables affect the growth rates of five coral species in three locations in the Colombian Caribbean.

Bravo used the AquapHOx-L-pH Logger with a pH sensor cap PHCAP-PK8T-SUB to research the pH level patterns in three different areas in Colombia where corals are present (Santa Marta, Islas del Rosario, and Providencia). These areas have different environmental conditions (like different levels of turbidity, sedimentation, nutrient concentrations, etc.) and were chosen based on their importance in building the three-dimensional structure of coral reefs.

The outcomes of this research, as visualized on the graphs below, highlighted the differences between the three areas as well as the existence of clear pH level dynamic patterns within two of them (Santa Marta and Providencia), but not the third one (Islas del Rosario). Underwater currents could be a possible explanation for the existence of similar patterns, whereas the different sediment/nutrient loads produced by the discharges of Magdalena river could explain the irregular patterns.

pH graph

These new insights provide data-backed knowledge about the frequency and span of the pH level changes and how they could potentially affect the well-being, growth, and survival of coral reefs, the most essential ecosystem builders and keepers in the ocean***.

*Source: “Understanding the Science of Ocean and Coastal Acidification” by US EPA

** Source: “Ocean Acidification” by UNESCO

*** Source: “The Importance of Coral Reefs” by NOAA

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