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Award Detail

Doing Business As Name:University of Georgia Research Foundation Inc
  • Brian Hopkinson
  • (706) 542-7880
  • William Fitt
  • Yongchen Wang Dr.
  • Christof D Meile
Award Date:06/07/2013
Estimated Total Award Amount: $ 307,378
Funds Obligated to Date: $ 312,328
  • FY 2016=$4,950
  • FY 2013=$307,378
Start Date:09/01/2013
End Date:08/31/2017
Transaction Type:Grant
Awarding Agency Code:4900
Funding Agency Code:4900
CFDA Number:47.074
Primary Program Source:040100 NSF RESEARCH & RELATED ACTIVIT
Award Title or Description:Ocean Acidification: Coral Inorganic Carbon Processing in Response to Ocean Acidification
Federal Award ID Number:1315944
DUNS ID:004315578
Program:Cellular Dynamics and Function
Program Officer:
  • Charles Cunningham
  • (703) 292-2283

Awardee Location

Street:310 East Campus Rd
Awardee Cong. District:10

Primary Place of Performance

Organization Name:University of Georgia
Cong. District:10

Abstract at Time of Award

A significant portion of the carbon dioxide generated by human activity and released into the atmosphere dissolves into ocean waters, leading to ocean acidification. Acidification can impair the ability of many calcifying organisms, including reef-building corals, to form their calcium carbonate shells or skeletons but the mechanism of these effects is not well understood. This project will improve understanding of inorganic carbon processing in corals thereby providing insight into the effects of ocean acidification on calcification and photosynthesis in corals. Microelectrodes and membrane inlet mass spectrometry (MIMS) will be applied to measure the concentration and reaction rates of inorganic carbon and other chemical species involved in calcification and photosynthesis in three species of Caribbean corals. A major goal is to validate the use of MIMS techniques and microelectrodes in corals. Measurements will be used to develop a numerical model of inorganic carbon processing in corals, allowing chemical fluxes and the composition of the calcifying fluid to be constrained. Improved mechanistic understanding of the effects of ocean acidification on corals will permit robust predications about the longer-term effects of ocean acidification on corals and coral reefs. Broader Impacts: This project will improve predictions of the effects of ocean acidification on corals and coral reef ecosystems. Undergraduate and graduate students will be trained on the project and outreach activities include educating K-12 students and the general public about ocean acidification. A teaching module on the effects of ocean acidification on corals will be added to an existing set of ocean acidification lesson plans and a collaboration with the Driftwood Education Center will be established to make use of the ocean acidification teaching module. The investigators will host an annual mini-symposium called "Symbiofest", which attracts scientists working on corals and other symbioses from around the south-east and beyond.

Publications Produced as a Result of this Research

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Tansik, A. L. Fitt, W. K. Hopkinson, B. M. "Inorganic carbon is scarce for symbionts in scleractinian corals" Limnology and Oceanography, v.62, 2017, p.2045. doi:10.1002/lno.10650 

Hopkinson, B. M. Tansik, A. L. Fitt, W. K. "Internal carbonic anhydrase activity in the tissue of scleractinian corals is sufficient to support proposed roles in photosynthesis and calcification" Journal of Experimental Biology, v.218, 2015, p.2039.

Tansik, AL Fitt, WK Hopkinson, BM "External carbonic anhydrase in three Caribbean corals: quantification of activity and role in CO2 uptake" Coral Reefs, v.34, 2015, p.703.

Cai, W.J., Y. Ma, B. M. Hopkinson, A.G. Grottoli, M.E. Warner, Q. Ding, X. Hu, X. Yuan, V. Schoepf, H. Xu, C. Han, T.F. Melman, K.D. Hoadley, D.T. Pettay, Y. Matsui, J.H. Baumann, S. Levas, Y. Ying, and Y. Wang. "Coral interior carbonate chemistry and dynamics as revealed by CO32- and pH microeletrode measurements" Nature Communications, v.7, 2016, p.11144.

Project Outcomes Report


This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

            A portion of the CO2 released into the atmosphere by human activities dissolves in the ocean where it reacts with water to produce carbonic acid. This results in a reduction of the pH of seawater and a host of other chemical changes known as ocean acidification. In corals, ocean acidification reduces the formation rate of the calcium carbonate skeleton, and consequently growth.  The detrimental effects of ocean acidification are compounded by numerous stressors harming coral reefs including high temperature-induced bleaching, overfishing, and nutrient pollution.

This project sought to develop and apply new methods to determine the flows of inorganic carbon (CO2, HCO3-, CO32-) that supply inorganic carbon for new skeletal growth and photosynthesis in corals. Changes in these flows are likely a critical component of the response of corals to ocean acidification. The long-term goal of this research is to identify the mechanism by which ocean acidification reduces rates of skeletal growth. Work was primarily conducted in three areas: 1) modifying and applying membrane inlet mass spectrometry (MIMS) approaches that have been used to study inorganic carbon flows in microalgae to corals, 2) applying advanced microelectrode profiling methods to directly measure relevant chemicals in corals (H+, CO32-, Ca2+), and 3) developing numerical models that integrate these results to produce a unified view of inorganic carbon flows that support new skeletal growth and photosynthesis in corals.

In microalgae, powerful MIMS methods have been developed that allow selected inorganic carbon flows and carbonic anhydrase activities to be measured directly. Carbonic anhydrase is an enzyme, pervasive in inorganic carbon delivery pathways, that catalyzes the hydration of CO2 and dehydration of HCO3-. We modified and extended these methods to corals, developing new models to analyze data on macroscopic organisms such as corals. We showed that corals possess an external, surface-associated carbonic anhydrase that converts HCO3- to CO2 for use in photosynthesis. This pathway supplies about half of the CO2 for net photosynthesis.  Using these newly developed methods, internal carbonic anhydrase activity was measured and found to be quite high in coral tissues. Current conceptual models of inorganic carbon processing in corals posit multiple, critical roles for these internal carbonic anhydrases. Our work showed that there is sufficient carbonic anhydrase activity in coral tissues to fulfill these proposed roles. Finally, we showed that inorganic carbon is scarce for algal symbionts of corals, through measurements of inorganic carbon affinities of corals and isolated symbiotic algae. This finding is surprising given the abundance of inorganic carbon in seawater, and we hypothesize that coral hosts limit the inorganic carbon supply to their symbionts to control photosynthesis.

Directly determining the concentration of inorganic carbon and related chemical forms within corals is extremely difficult. Microelectrodes are one tool that can provide such data, but their use requires much experimentation and care. We used microelectrodes sensitive to CO32-, H+, and Ca2+ to continuously measure these chemicals in corals as the microelectrode was passed through coral tissue. With this approach, we were able to directly measure the CO32- concentration in the calcifying fluid of corals for the first time. Coral skeletons are made of calcium carbonate (CaCO3), which is precipitated from the calcifying fluid. Consequently, the CO32- concentration in the calcifying fluid partially controls the rate of new skeleton formation and may be modified by ocean acidification. Our measurements indicated that corals achieve rapid rates of calcification by raising pH to very high levels, while keeping total inorganic carbon concentrations in the calcifying fluid low. The microelectrode profiles produced an abundance of novel data, for further study.

The final focus of our work was integrative modeling to provide a more detailed understanding of inorganic carbon flows and probe ways in which these flows may change under ocean acidification. We developed a simple but powerful model of inorganic carbon processing in corals that represents the major biological compartments (diffusive boundary layer, oral tissue, coelenteron, aboral tissue, calcifying fluid) and fluxes (photosynthesis, calcification, bicarbonate transport, CO2/HCO3- interconversion). The model was constrained with data from the literature and new information obtained as part of this project. The model is capable of reproducing observed rates of photosynthesis, calcification, and their isotopic compositions showing progress in understanding the magnitude of and interdependence between these processes.

Several graduate students participated in this project, including one student who obtained their PhD and one who obtained their masters working on this research. A new teaching module on ocean acidification was developed. A mini-symposium on symbiosis was held each year drawing participants from throughout the southeast.

In summary, this project advanced our understanding of inorganic carbon supply pathways in corals and provided new approaches to studying this and related processes. This research thus helps us to better understand how ocean acidification affects corals. 


Last Modified: 10/09/2017
Modified by: Brian Hopkinson

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