Natural submarine springs pouring onto one of the Caribbean's largest reef ecosystems are providing insight to the long-term responses of coral reefs to a more acidic ocean environment.
As levels of carbon dioxide build up in the atmosphere, it is not only leading to problems of climate change but it is also dissolving in the oceans causing the pH to drop - studies have already shown that the oceans have become 30% more acidic since the industrial revolution - that's the fastest rate of acidification in 55 million years.
Near shore springs called 'ojos' off the coast of the Yucatán Peninsula in Mexico have been discharging groundwater with naturally low-pH and low carbonate saturation near the Mesoamerican Barrier Reef for millennia. This phenomenon gives researchers the opportunity to examine, in the natural environment, the long term impacts of acidification on organisms, especially calcifying organisms such as reef-building corals. Lowering pH alters the balance of calcium carbonate in seawater, effectively reducing the concentration of carbonate ions that many marine organisms use to build shells and skeletons.
A research team led by Elizabeth Crook from the University of California Santa Cruz took water samples at varying distances from the ojos to measure temperature, salinity, pH, and nutrients. Data was also collected on the density and size of species living close to the ocean floor at varying distances from the ojo centers.
The three-year study, published in the journal Coral Reefs, measured a decrease in coral species diversity and a decline in the size of coral colonies in areas closer to the ojos. At all 10 ojo sites examined, three species of coral were observed that grow well in an acidic environment. Unfortunately these are rarely major contributors to the framework of this barrier reef. As ocean pH decreases the complex mix of coral species responsible for building the reef could be replaced by smaller, patchy colonies with reduced species diversity.
This study indicates that species response to ocean acidification will vary by location and species and highlights the need to understand the mechanisms corals use to take calcium on board even at lower pH. This will help build more accurate predictions of the future impacts of ocean acidification.
Find out more:
Crook, E.D. et al (2011). Calcifying coral abundance near low-pH springs: implications for future ocean acidification.
Coral Reefs, DOI 10.1007/s00338-011-0839-y
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