NSFDEB-NERC The blueprint for marine biomineralization in a changing climate

Understanding and quantifying the global carbon cycle (interchange of carbon between atmosphere, ocean, and land) is essential for predicting future concentrations of atmospheric carbon dioxide (CO2), which is responsible for about two thirds of global warming. The ocean absorbs over a third of the CO2 that enters the atmosphere by natural and human activity. As the concentration of atmospheric CO2 increases therefore, so does the concentration of CO2 dissolved in our oceans. This makes our oceans progressively less alkaline, in a process termed ocean acidification (OA). OA has serious consequences, particularly for those marine organisms that make calcium carbonate (calcite) shells (e.g., mussels and oysters) or structures (e.g., corals), because calcite dissolves in more acidic environments.

Some of the most globally important marine calcifying organisms affected by OA are microscopic single-celled animals called foraminifera. Foraminifera are widely distributed in marine systems and provide a major route for the removal of CO2 from the atmosphere through the long-term, deep-sea burial of their calcite shells. How ongoing ocean acidification and warming will affect the rate of foraminiferal calcification and calcite burial in coming decades, however, is currently poorly understood. This is largely because we do not understand how foraminifera calcify and how they will respond to future OA and ocean warming. As a result, it is not possible to confidently predict how climate change will impact the future carbon cycle and atmospheric CO2 concentrations.

This project will be the first ever to investigate the molecular mechanism that foraminifera use to build their shell, to discover how they calcify. The initiation of calcification in foraminifera occurs on a highly specialised organic membrane that forms a "bubble" on which the new shell layer is crystalized. We know that the proteins in the organic membrane are responsible for this process but not specifically which of the proteins present are responsible for calcite nucleation, or the environmental conditions required for this to occur. Our project has three major objectives. The first is to identify the organic membrane proteins by sequencing both the proteins and the genome (the complete set of DNA in the cell) of two model species of foraminifera. The second objective is to identify which of the organic membrane proteins are key in calcite nucleation and the third objective is to discover how these proteins behave under different environmental conditions.

Fulfilling our objectives will enable us for the first time to identify the critical genes and proteins that drive calcification in the foraminifera, and their response to ocean acidification. This exciting project will provide biologists with the first complete set of gene sequences (the genome) of the foraminifera, which provides all the information they require to function. The availability of genomes is a fundamental requirement for the study of any organism and will significantly improve and increase the kinds of studies that can be carried out, substantially advancing our understanding of foraminiferal biology. These genomes will be publicly available via continued open access in online databases for the advancement of research. Discovering the proteins responsible for calcification and how they are controlled and respond to environmental changes will above all, enable us to assess foraminiferal susceptibility to climate change in the future. It will equip scientists with the capability to more confidently predict how climate change will impact the future carbon cycle and atmospheric CO2 concentrations.