Examining the life cycle of coccolithophores

Project Rationale:
Coccolithophores are abundant marine phytoplankton that are characterized by their ability to form a covering of calcium carbonate plates or coccoliths. Calcification by coccolithophorid algae plays an important role in the global carbon cycle, contributing to the export of carbon from the surface ocean. Despite their importance to global biogeochemical cycles, many aspects of coccolithophore biology remain poorly understood. Coccolithophores exist in two distinct life cycle stages (haploid and diploid), but we do not understand the ecological and physiological significance of this.
There is some evidence that haploid and diploid forms of each coccolithophore species are found in distinct marine environments, suggesting that these life cycle stages may be adaptions to allow coccolithophores to exploit alternative ecological niches. This project will examine the physiological differences between coccolithophore life cycle stages, focusing on species such as Coccolithus braarudii and Calcidiscus leptoporus that are abundant in Atlantic Ocean but are currently poorly characterized. In addition to these laboratory studies, the project will also explore the distribution of the life cycle stages in the environment, via examination of samples obtained on research cruises and from the MBA’s weekly sampling regime in the Western English Channel (Western Channel Observatory).


Methodology:
-Physiology of coccolithophore cultures
Haploid and diploid cultures of Coccolithus braarudii and Calcidiscus leptoporus will be grown under differing light and nutrient regimes to examine how each life cycle stage differs in its ability to tolerate stresses. Initial experiments will measure growth rate (cell counts) and productivity. More detailed analyses will involve studying effects of these stresses on photosynthesis (chlorophyll fluorimetry, oxygen evolution) and cell morphology (light microscopy). In addition, the calcification status of the cultures will be assessed by scanning electron microscopy to look at the effects of stress on the production of coccoliths.

-Environmental samples
To complement the laboratory studies detailed above, we will also examine the relative prevalence of haploid/diploid coccolithophores in environmental samples. This work will be initiated by analyzing weekly samples from the Western English Channel (station L4) for the relative presence of each life cycle stage. Filtered seawater samples will be directly observed by scanning electron microscopy. In addition, molecular analyses (qPCR) will be used to detect the presence of the different cell types in seawater samples. These techniques will then be applied to environmental samples taken on a research cruise in an area where these species are abundant (e.g. temperate Atlantic Ocean).

Training:
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at Marine Biological Association, Plymouth, UK. Specific training will include:
-Phytoplankton culturing techniques. The student will receive be trained in the culturing of marine phytoplankton, in particular in the design and implementation of nutrient limitation experiments.
-Physiological analyses. Full training will be provided in methods to measure coccolithophore physiology (photosynthesis, respiration, calcification, cell morphology)
-Environmental sampling. Training will be provided in environmental sampling techniques, including the opportunity to visit the Western English Channel aboard the MBA’s own research vessel (MBA Sepia), as well as an extended research cruise in the Atlantic Ocean.
-Molecular biology. The student will be trained in molecular techniques such as quantitative polymerase chain reaction (qPCR) to enable detection of different life cycle stage sin environmental samples.
-Scanning electron microscopy. Training will be provided in scanning electron microscopy to enable detailed examination of coccolith morphology under different experimental regimes.