FY 2006

Impacts of ocean acidification on coral reefs and other marine calcifiers: A guide to future research

Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins

Report of a workshop held 18–20 April 2005, St. Petersburg, FL, sponsored by NSF, NOAA, and the U.S. Geological Survey, 88 pp (2006)

Executive Summary

Research findings of the past decade have led to mounting concern that rising atmospheric carbon dioxide (CO₂) concentrations will cause changes in the ocean's carbonate chemistry system, and that those changes will affect some of the most fundamental biological and geochemical processes of the sea. Thanks to the efforts of large-scale physical and biogeochemical ocean programs such as WOCE, JGOFS, and OACES, ocean-wide changes in the carbonate system are now well documented. Since 1980 ocean uptake of the excess CO₂released by anthropogenic activities is significant; about a third has been stored in the oceans. The rate of atmospheric CO₂ increase, however, far exceeds the rate at which natural feedbacks can restore the system to normal conditions. Oceanic uptake of CO₂ drives the carbonate system to lower pH and lower saturation states of the carbonate minerals calcite, aragonite, and high-magnesium calcite, the materials used to form supporting skeletal structures in many major groups of marine organisms.

A variety of evidence indicates that calcification rates will decrease, and carbonate dissolution rates increase, as CaCO₃ saturation state decreases. This evidence comes from principles of thermodynamics, the geologic record, and the evolutionary pathways of CaCO₃ secreting organisms. Further evidence, from controlled experiments of biocalcification under increased CO₂ conditions, confirms that calcification rates of many organisms decrease with decreasing CaCO₃saturation state. Extrapolation of these results to the real world suggests that calcification rates will decrease up to 60% within the 21st century. We know that such extrapolations are oversimplified and do not fully consider other environmental and biological effects (e.g., rising water temperature, biological adaptation); nor do they address effects on organism fitness, community structure, and ecosystem functioning. Any of these factors could increase or decrease the laboratory-based estimates, but it is certain that net production of CaCO₃ will decrease in the future.

The St. Petersburg Workshop, sponsored by NSF, NOAA, and the USGS, and held at the USGS Center for Coastal and Watershed Studies on 18–20 April 2005, was designed to take the next step toward understanding the response of marine calcification to increasing atmospheric CO₂ concentration. The aims of the workshop were to summarize existing knowledge on the topic, reach a consensus on what the most pressing scientific issues are, and identify future research strategies for addressing these issues. Although workshop participants were drawn from a wide range of scientific disciplines, there was a clear convergence on the major scientific issues that should be pursued over the next 5–10 years. These include:

• Determine the calcification response to elevated CO₂ in benthic calcifiers such as corals (including cold-water corals), coralline algae, foraminifera, molluscs, and echinoderms; and in planktonic calcifiers such as coccolithophores, foraminifera, and shelled pteropods;
• Discriminate the various mechanisms of calcification within calcifying groups, through physiological experiments, to better understand the cross-taxa range of responses to changing seawater chemistry;
• Determine the interactive effects of multiple variables that affect calcification and dissolution in organisms (saturation state, light, temperature, nutrients) through continued experimental studies on an expanded suite of calcifying groups;
• Establish clear links between laboratory experiments and the natural environment, by combining laboratory experiments with field studies;
• Characterize the diurnal and seasonal cycles of the carbonate system on coral reefs, including commitment to long-term monitoring of the system response to continued increases in CO₂;
• In concert with above, monitor in situ calcification and dissolution in planktonic and benthic organisms, with better characterization of the key environmental controls on calcification;
• Incorporate ecological questions into observations and experiments; e.g., How does a change in calcification rate affect the ecology and survivorship of an organism? How will ecosystem functions differ between communities with and without calcifying species?
• Improve the accounting of coral reef and open ocean carbonate budgets through combined measurements of seawater chemistry, CaCO₃ production, dissolution and accumulation, and, in near-shore environments, bioerosion and off-shelf export of CaCO₃;
• Quantify and parameterize the mechanisms that contribute to the carbonate system, through biogeochemical and ecological modeling, and apply such modeling to guide future sampling and experimental efforts;
• Develop protocols for the various methodologies used in seawater chemistry and calcification measurements.

Some of these research objectives require technological development, but others can be addressed immediately. While much work remains toward answering the fundamental question: "How will marine calcification rates respond to increasing atmospheric CO₂ concentrations," we need to begin investigations that look forward to answering the question: `"What are the consequences of reduced calcification in both planktonic and benthic calcifying communities and ecosystems?" We should not wait until we answer the former question before tackling the latter.

This report is intended as a guide to program managers and researchers toward designing research projects that address these important questions. It is written with the detail and references needed to serve as a resource for researchers, including graduate students, who wish to tackle projects within the sometimes confusing topic of marine carbonate chemistry and calcification.