70 years of helping people to care for our ocean

Monitoring ocean acidification on the southern-most coral reefs in the Western Indian Ocean

By :  Sean Porter

By now most of us reading this article have heard of climate change and global warming, and the devastating effects it has on corals, causing them to bleach and often die. But what many of us are unaware of is that the excess carbon dioxide in the atmosphere, resulting from the burning of fossil fuels, has other impacts on the oceans as well. The excess carbon dioxide in the atmosphere is absorbed by the oceans which in turn alters their chemistry, making them more acidic. Ocean acidification is problematic for many organisms such as corals that accrete a calcium carbonate skeleton, as it makes it more difficult for these habitat forming organisms to maintain their skeleton and the overall structure of the reef.

Six months ago, the Oceanographic Research Institute initiated ocean acidification monitoring on the reefs at Sodwana Bay and recently returned from a follow-up field trip. This most recent trip involved servicing the SeapHoX probe which measures the pH or acidity of the seawater every hour. The team also undertook routine water sampling for carbonate chemistry and retrieved all the accretion tiles and coral nubbins that were deployed six months ago. A new batch of accretion tiles and coral nubbins were also deployed which will be used to assess accretion and dissolution during the cooler winter period.

The accretion tiles and coral nubbins were all meticulously weighed and labelled before they were deployed. Now that the first batch have been retrieved, they will be analysed for the amounts of calcium carbonate they have accreted or lost over the last six months. This information will be coupled with the carbonate chemistry of the water samples that have been routinely collected using mathematical models that the team hopes to be able to use to forecast the effects of ocean-acidification-linked climate change on our local reefs into the future. This will enhance our understanding of the implications ocean acidification will likely have on the livelihoods of coastal communities that rely on coral reefs for tourism, ecosystem services and resources.