PhD title: Effects of ocean acidification on shell characteristics in articulated brachiopods.
Description: The oceans are a natural sink for CO2, resulting in vast reservoirs far greater than either the atmospheric or terrestrial system. Since the industrial revolution, atmospheric carbon dioxide has been rising at a faster rate that the Earth has ever experienced and the oceans have absorbed 50% of the total carbon dioxide released through burning fossil fuels and other human activities. While this has mitigated global warming, it has caused the oceans to become more acidic. This has resulted in the current average surface ocean pH to have decreased by 0.1 pH units (~30% increase in hydrogen ion concentration) over the last 250 years. Increased oceanic diffusion of atmospheric carbon dioxide affects the carbonate chemistry and alters the balance of bicarbonate:carbonate ions. This reduction in the availability of carbonate ions will make it more difficult and/or require marine calcifying organisms to use more energy to make their integral calcium carbonate structural components such as skeletons and shells. Therefore, calcifying organisms are amongst the most susceptible marine organisms to ocean acidification which potentially could result in changes in biodiversity, trophic interactions and other ecosystem processes.
Living articulated brachiopods inhabit all of the world’s oceans from the poles to the tropics, and from the deep sea to the intertidal. This phylum is possibly the most calcium carbonate dependent on Earth due to over 90% of their dry mass is in their calcareous shell. General brachiopod attributes including low feeding rates, low metabolic rates, slow growth and deferred maturity also result in a lower likelihood of these organisms producing adaptations to cope in acidified conditions in comparison to other marine invertebrates. They are well represented and have a high abundance in fossil records over long geological periods. Due to their excellent preservation and fossil record in addition to their abundant extant species, brachiopods are excellent study organisms to explore how shell characteristics vary with seawater pH in relation to current variation between sites and long term variations in pH since the industrial revolution and over geological time.
This project aims to address four main questions:
1. How do shell microstructure and composition (thickness, primary & secondary layer thickness, crystal morphology, major & minor elements) vary between conspecifics living in current different pH sites?
2. How do these shell characteristics vary within a species from the same site across the Anthropocene?
3. How do shell microstructure and composition vary in articulated brachiopods across geological periods with markedly different atmospheric CO2 levels?
4. How does growing articulated brachiopods in lowered pH conditions alter their shell characteristics?
This project is funded by NERC and is part of the NERC Thematic Programme to investigate biodiversity and ecosystem functioning on the planet.
Supervisors: Dr Liz Harper and Prof Lloyd Peck (British Antarctic Survey)