Coccolithophorids are a group of unicellular plant plankton, which surround themselves with minute and highly structured calcite plates, called coccoliths. Coccolithophorids abound in all oceans of the world. In terms of calcium carbonate production, they are undoubtedly the major contributor to the ocean sediments (1), today accounting for about a third of the total marine CaCO3 production (2). The most abundant coccolithophore species is Emiliania huxleyi, shown on the left on the top of Figure 1.
Figure 1. Various coccolithophorids from Jeremy Young’s web page, at the National History Museum, London, UK. All scale bars are 1 micron. From left to right: Emiliania huxleyi whole coccolithophorid cell surrounded by its coccoliths, Calcidiscus leptoporus ssp. quadriperforatus; detail of a coccolith spine from Rhabdosphaera clavigera, details of coccoliths from Syracosphaera molischii, Algirosphaera robusta, and Discosphaera tubifera, respectively. The exquisite control on the nanostructures formed by coccolithophorids, and the principles regulating such control are still unexplored, and may be relevant to synthetic nanofabrication efforts.
E. huxleyi may very well be the most abundant calcium carbonate producing species on earth (3). Coccolithophorid blooms, mostly composed of E. huxleyi can be seen from satellite, as presented in Figure 2. The biogeochemical impact of coccolithophorids is amplified by export of coccoliths to the ocean floor, where coccoliths are the largest single component of deep-sea sediments, forming vast accumulations of calcareous oozes and chalks, including the Late Cretaceous chalks of NW Europe (4) (Figure 1). Over the past 220 years there has been a 40% increase in average coccolith mass (2).
Figure 2. Left and middle: coccolithophore blooms seen from satellite in the Celtic Sea and the Bering Sea. The high density of coccolithohorids provides a white background, thus sea water appears cyan, as it absorbs the complementary color red. Righ: The white cliffs of Dover, in SE England, composed mostly of sedimented coccoliths.
Coccolith biomineralization has been extensively studied. Recent reviews include (4-9).
Coccoliths present a very unnatural morphology for calcite, yet they are composed of calcite single crystals, as shown in Figure 1.
Iglesias-Rodriguez et al. recently showed that coccolithophorids are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate (2).
Coccolithophorids are responsible for the vast majority of biogenic calcification in marine systems. Results from recent marine paleontology and culture-based studies suggest that different coccolithophore species respond differentially to varying levels of nutrients, pCO2, bicarbonate, etc. (10). However, surprisingly little is known about the effect of such local environmental factors on biomineralization (11). The first coccolithophore genome sequence (of E. huxleyi) and several expressed sequence tag libraries have created an unprecedented opportunity to investigate the genetic and biochemical mechanisms responsible for biomineralization.
We are initiating in vitro experiments on E. huxleyi CO2 sequestration, and plan to correlate efficiency in CO2 removal from atmosphere and gene regulation.