Behind the Cover: New Phytologist 220:1, October 2018

To calcify, or not to calcify?

Often, it’s the smallest things, when taken together, that have the largest impacts. Calcification in the oceans – when calcium accumulates in the body tissues of an organism – is a major sink of carbon dioxide (CO2), and an important influence on the global carbon cycle. Calcification is a key aspect of the biology of the coccolithophores – a group of single-celled photosynthetic algae, which transform some of the CO2 they absorb into minute scales made of calcium carbonate. Coccolithophores cover themselves with these scales, called coccoliths, forming a kind of ‘shell’ around the cell.

 

Image: An SEM image of a mineralized scale of the most abundant calcifying phytoplankton, Emiliania huxleyi. Courtesy of Assaf Gal.
An SEM image of a mineralized scale of the most abundant calcifying phytoplankton, Emiliania huxleyi. Courtesy of Assaf Gal.

Coccolithophores exist in vast numbers in the oceans. The image on the cover of New Phytologist 220:1 shows just one tiny coccolith. The exact physiological role of these scales remains a bit of a mystery, but it’s clear that their production in massive number has important implications for the global carbon cycle. However, some coccolithophores are more likely to calcify than others.

 

In the paper behind the image on the cover, Dr Charlotte Walker and colleagues describe how they discovered that the need to calcify differs between two coccolithophore species, Emiliania huxleyi and Coccolithus braarudii. The researchers designed a clever experiment to take advantage of the E. huxleyi‘s notorious fussiness when it comes to growing conditions – the species is known to be difficult to culture in the lab. By stopping the coccolithophores from producing coccoliths, they found that E. huxleyi was able to continue functioning after calcification had stopped. In contrast, in C. braarudii, calcification was so tightly linked to the cell cycle that the coccolithophore stopped growing entirely.

Coccolithophores are useful for studying the past geochemical cycles of the planet, as well as the effects of current changing climate conditions. The results of this study by Dr Walker and colleagues will be useful for making predictions about the future of these important carbon-fixing organisms in our changing oceans.

Read the paper: Walker, C. E., Taylor, A. R., Langer, G. , Durak, G. M., Heath, S., Probert, I., Tyrrell, T., Brownlee, C. and Wheeler, G. L. (2018) The requirement for calcification differs between ecologically important coccolithophore species. New Phytologist. doi: 10.1111/nph.15272

Read the Commentary: Gall, A. (2018) Looking away from the streetlight – new insights into marine calcificationNew Phytologist. doi: 10.1111/nph.15409

Find out more about coccolithophores and calcium in this Royal Institution video by Helen Czerski:

 

Dr Mike Whitfield
Development Coordinator
New Phytologist Trust