Research Highlight: Scripps Scientists Think Outside the Tank

Experimental field system successfully replicates the effects of pH declines on coral reef ecosystems

Researchers at Scripps Institution of Oceanography at UC San Diego have reported a breakthrough in measuring the effects of ocean acidification on coral reefs using a new experimental system that can simulate future ocean chemistry in a natural reef setting.

Scripps marine biologist Davey Kline reported in a new paper published in Scientific Reports that the new system, called CP-FOCE, will overcome a major barrier to the study of changes in ocean chemistry.  Previous research on the effects of ocean acidification on the barrier reef has taken place in aquarium settings, but there are many environmental and ecological conditions that cannot be realistically reproduced in such studies, Kline said.

“There is an urgent need for in situ studies to perform the experiments in the environment where the organisms occur naturally,” said Kline, an assistant project scientist at Scripps.  “However, manipulating CO₂ levels in the field to those predicted for the future poses several science and engineering challenges.”

The years since the Industrial Revolution have seen more than a hundred-fold increase in the rate of CO₂ released into the atmosphere.  The world’s oceans have absorbed nearly 30 percent of that CO₂, resulting in a decline in oceanic pH.  Scientists believe that this process, termed ocean acidification, will inevitably affect life in the oceans.  Some organisms are more sensitive than others to lower pH, particularly those building a hard shell or skeleton.

In the last 200 years, the pH of the open ocean has dropped from 8.2 to 8.1 pH units, a seemingly small trend.  But because the pH scale is logarithmic, a 0.1 change in pH represents approximately a 30 percent increase in the number of hydrogen ions that are available.  That’s a massive alteration to the chemistry of the ocean, Kline said.

The study evolved out of a review of previous systems that have manipulated conditions in the field.

The Free Atmospheric CO₂ Enrichment (FACE) studies have been implemented in plant ecosystems all over the world for the last 20 years.  In earlier studies, scientists installed rings of CO₂-emitting devices in terrestrial forests around the globe, which release CO₂ into sections of the forest at levels that simulate projected CO₂ emissions for the future.  The changes created by these CO₂ emissions are then observed, and plant responses to elevated CO₂ can be investigated without disturbing plant interactions with light, water or animal life.

Peter Brewer of the Monterey Bay Aquarium Research Institute engineered the FACE system to do the same experiments in the ocean, up to depths of several thousand meters off the coast of Monterey, Calif.  Kline and Brewer worked together to design a similar system that would be effective in shallow marine environments, as well as work around the challenging conditions that occur on coral reefs.

The paper describes a five-day study, the first experiment using the new system, which found that the CP-FOCE was able to maintain the predicted chemistry of the seawater, as well as monitor and replicate the daily fluctuations in pH levels that occur naturally on the coral reef.

According to Kline, the results from long-term CP-FOCE experiments will help scientists understand the effects of ocean acidification on the coral reef ecosystem level for the first time, including the corals, fish, algae, other invertebrates and their interactions.

- Deborah L. Jude

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