Monterey Bay Aquarium Research Institute

Adina Paytan, PhD

University of California, Santa Cruz

Calcifying coral abundance near low-pH springs:
Implications for future ocean acidification

Wednesday — March 28, 2012
Pacific Forum — 3:00 p.m.

Rising atmospheric CO2 and its equilibration with surface ocean seawater is lowering both the pH and carbonate saturation state of the oceans. Numerous calcifying organisms, including reef-building corals, may be severely impacted by declining aragonite and calcite saturation, but the fate of coral reef ecosystems in response to ocean acidification remains largely unexplored.

Naturally low-saturation, low-pH groundwater has been discharging for millennia at localized submarine springs (called "ojos") at Puerto Morelos, Mexico, near the Mesoamerican Reef. This ecosystem provides insights into potential long-term responses of coral ecosystems to low saturation conditions. In situ chemical and biological data indicate that both coral species richness and coral colony size decline with increasing proximity to low-saturation, low-pH waters at the ojo centers. Only three scleractinian coral species (Porites astreoides, Porites divaricata, and Siderastrea radians) occur in undersaturated waters at all ojos examined.

Because these three species are rarely major contributors to Caribbean reef framework, these data may indicate that today’s more complex frame-building species may be replaced by smaller, possibly patchy, colonies of only a few species along the Mesoamerican Barrier Reef. Calcification rates also drop at the low pH springs. The growth of these scleractinian coral species at undersaturated conditions illustrates that the response to ocean acidification is likely to vary across species and environments; thus, our data emphasize the need to better understand the mechanisms of calcification to more accurately predict future impacts of ocean acidification.


Next: April 4—Steve Rock, PhD