Unlocking the inner cell: Elemental stoichiometry
of coccolithophores


The elemental building blocks of marine life include carbon, nitrogen and phosphorus, which form cellular structures and drive metabolic processes. The availability of these elements in the marine environment dictates patterns of nutrient limitation in space and time, while the cycling of elements through marine algal (phytoplankton) uptake and release is fundamental to oceanic biogeochemical cycles, as well as the coupling between the different elemental cycles. Coccolithophores are a key phytoplankton group in terms of ocean biogeochemistry, forming both organic matter and calcium carbonate in the form of calcite scales that they adorn to the inner organic cell. Thus, coccolithophore cells have a dual personality as they perform both photosynthesis and calcification, and likely require a typical algal recipe for their organic cells, as well as large amounts of calcium and carbon for their scales. Their reliance on calcium carbonate for cell structures puts coccolithophores at the forefront of phytoplankton groups potentially impacted by changes in ocean pH (Ocean Acidification), with many studies showing reduced calcification whilst photosynthetic rates may be enhanced or remain unchanged. Due to such potential changes in coccolithophore calcite production, there is a need to better understand their wider role(s) in biogeochemical cycles, for example by examining their fundamental nutritional ecology and elemental composition.

Whilst several seminal publications exist on the elemental composition of different phytoplankton groups, very little data exists across the diversity of cell size, geological age, oceanic niche or calcite content of the coccolithophores. There are also now several lines of evidence indicating that many coccolithophore species are not strictly autotrophic, and may in fact utilize either dissolved or particulate organic material to access essential nutrients. This studentship will ‘unlock the inner cell’ of coccolithophores by gaining new insights into their elemental composition and contribution to global biogeochemical cycles. It will also ‘rip up the rule book’ on their nutrition by looking for new pathways of elemental flow between coccolithophores and their environment.

This PhD project will examine the elemental composition of different species who differ in cell-size and calcite content under varying nutrient and irradiance conditions in laboratory cultures. The student will utilize state-of-the-art seawater aquarium and novel geochemical analytical facilities at the Lyell Centre for Earth and Marine Science and Technology, part of Heriot-Watt University. The project will use stable isotopes and radioisotopes to measure rates of photosynthesis and calcification, as well as nutrient uptake and recycling by coccolithophore cells. Specific training will include: Coccolithophore cultivation, ecology, physiology and taxonomy; biochemical analysis of major elements and macromolecular composition; Use of stable and radioactive isotopes to measure calcification, photosynthesis and nutrient recycling. Fieldwork opportunities could include tropical shelf-sea waters (Singapore) and/or the temperate open-ocean (NE Atlantic).

Relevant references

  • Daniels et al. (2014). Biogeochemical implications of comparative growth rates of Emiliania huxleyi and Coccolithus species. Biogeosciences 11, 6915-925, doi: 10.5194/bg-11-6915-2014.
  • Monteiro et al. (2016). Why marine phytoplankton calcify. Science Advances 2, e1501822, doi: 10.126/sciadv.1501822.
  • Poulton et al. (2017). Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic Meridional Transect (AMT) programme. Progress in Oceanography, in press, doi: 10.1016/jpocean.2017.01.003.

Funding Notes

This is a full scholarship which will cover tuition fees and provide an annual stipend of approximately £14,500 for the 36 month duration of the studentship. The funding is available to UK, EU and international students.


To be eligible, applicants should have a first-class honours degree or a 2.1 honours degree plus Masters (or equivalent) in a relevant subject. Applicants with an Earth and/or Ocean Sciences background, including biogeochemistry/marine geoscience related qualifications and an interest in marine ecology and biogeochemistry are particularly encouraged. Scholarships awarded by competitive merit, taking into account the academic ability of the applicant.

How to Apply

Please complete our online application form.

Please select PhD programme Marine Biology and include the full project title, reference and supervisor on your application form. You will also need to provide a CV, a supporting statement, a copy of your degree certificate and relevant transcripts and an academic reference. You must also provide proof of your ability in the English language (if English is not your mother tongue or if you have not already studied for a degree that was taught in English). We require an IELTS certificate showing an overall score of at least 6.5 with no component scoring less than 6.0 or a TOEFL certificate with a minimum score of 90 points.

Informal enquiries should be addressed to the supervisor, Dr Alex Poulton at a.poulton@hw.ac.uk.


The closing date for applications is 31 January 2018. Interviews will be held in February 2018. The project start date is flexible, but should start no later than October 2018.

posted: 24 November 2017     Please mention EARTHWORKS when responding to this advertisement.