Ocean acidification

Anthropogenic CO2 has already caused ocean pH to decrease by an average of 0.1 units and by 2100 is projected to fall by 0.5 pH units. The marine environment contains an abundance of biomineralising organisms. As many marine biominerals are carbonate-based, current projections indicate that ocean acidification will catastrophically limit the ability of organisms to biomineralise. Without these biominerals, organism function would be critically inhibited.

Ocean ecosystems are highly complex, involved in climate regulation and provide critical resources. Many of these processes are dependent on marine biomineralisation e.g. primary production (supporting fisheries), tourism (coral reefs) and bivalve fisheries. All of these major processes are at risk from ocean acidification. Biogenic calcium carbonate is abundant in the marine environment where organisms such as coccoliths, corals and molluscs produce calcium carbonate structures. These carbonate structures are composed predominantly of the most common calcium carbonate polymorphs in the biosphere (calcite and aragonite) as exemplified by the common blue mussel, Mytilus edulis.

Critically, calcium carbonate minerals dissolve at low pH with meta-stable aragonite being more susceptible than calcite. The vulnerability of such carbonate biominerals is of great concern from the point of view of biodiversity and in terms of the rôle of the oceans as a CO2 sink. Thus, perturbation of biocalcification in such systems has potentially wide-reaching consequences. It is thus imperative that we fully understand the impact that ocean acidification will have upon this vital biomineralisation process.

Geochemistry & Biology
Concerns that ocean acidification will inhibit marine biogenic carbonate growth are largely based on geochemical grounds –i.e. that the carbonate concentration is decreasing in the ocean surface. However, biomineral growth is not simply driven by calcium carbonate saturation. Living systems exert exquisite control on the production of biominerals, determining the morphology, mineralogy and crystallography. Central to this control are specific proteins that are responsible for catalyzing nucleation and growth and growth inhibition. The exact expression of these proteins is critical to the controlled growth of the biomineral. In this way, organisms produce highly controlled, complex and striking mineral arrangements. Consequently, to unravel how ocean acidification will affect biominerals, we must examine its impact on the expression of biomineralising proteins and the complex biomineral structures that they produce. In short, to understand the impact of ocean acidification on biomineralisation, geochemical and biological controls cannot be treated separately.

Mytilus edulis
The shell of the common blue mussel, Mytilus edulis is composed of roughly equal proportions of calcite and aragonite. M. edulis is therefore an ideal system in which to determine the influence of ocean acidification on both calcite and aragonite in a biological system. This project aims to understand how both the protein and mineral components of M. edulis respond to ocean acidification with the identification of thresholds and tipping points in this response. This will enable us to move towards a more systems based understanding of how ocean acidification actually impacts on marine biomineralisers.

Professor Maggie Cusack, Dr Vernon Phoenix, Dr Nick Kamenos
University of Glasgow

Maggie was awarded a Research Project Grant in March 2011; providing £255,234 over 42 months.

The Leverhulme Trust News, web site.

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