Coccolithus pelagicus
Classification
Eukaryota; Haptophyta; Prymnesiophyceae; Coccolithales; Coccolithaceae
Species
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NCBI: [1] |
Coccolithus pelagicus
Description and Significance
Coccolithus pelagicus is one of over 200 species of coccolithophore (Monteiro et al, 2016). They are the most productive oceanic calcifiers in the world. Like other coccolithophores, Coccolithus pelagicus is a unicellular, eukaryotic phytoplankton that is characterized by distinctive calcite scales. These calcite scales are known as coccoliths, which cover each individual cell like an exoskeleton. Research has shown that coccoliths are important for coccolithophores in the context of physical armor protection against grazers and phages, as well as accelerated photosynthesis processes. C. pelagicus harbors natural tendencies that combat climate change. Calcification and photosynthesis require removing carbon from the ambient environment, both processes that C. pelagicus takes part in. Additionally, blooms of C. pelagicus reflect large amount of visible light traveling towards the ocean surface. This reflected light lowers the earth's albedo, thus lowering the amount of heat stored in the ocean.
C. pelagicus is found in Arctic and Subarctic cold waters across the North Atlantic and North Pacific (Mcintyre and Bé, 1967) with a minimal temperature of -1.7°C and an optimal temperature of 8°C (Baumann et al, 2000). However, coccospheres from this species have been reported in the Mediterraean (Daniels, 2015) and in New Zealand. It is a major calcite producer in its North Atlantic range despite being less abundant than other calcifiers such as E. huxleyi (Daniels, 2015). C. pelagicus rarely dominates the phytoplanktonic community and has relatively low abundance (Poulton et al, 2006) but blooms have been reported in shallow waters with concentrations up to 106 cells per L (Milliman, 1980). Concentrations of C. pelagicus can also be found near upwellings, or areas where wind drives denser, cooler water from ocean depths to the ocean surface (Ziveri et al, 2004).
Genome Structure
The genome of Coccolithus pelagicus has not yet been sequenced, and little is known about its genomic content. Emiliana huxleyi is another coccolithophore closely related to C. pelagicus that has a 167.7 Mb sequenced genome assumed to be similar to C. pelagicus. E. huxleyi has over 30,000 putative genes, with many of them providing functions related to carbon and calcium transport, as well as metabolism (Read et al, 2013).
Cell Structure, Metabolism and Life Cycle
Cell Structure
The C. pelagicus cell is spherical in shape. It contains two flagella, which is about 20 um long< and one haptonema (5-8 um) in between the flagella (Taylor et al., 2007). These structural features are present when the cell is in its motile phase since they are necessary for the cell to swim around. The haptonema can be in either an extended or coiled state. The cells have a plasma membrane which are layered with scales and coccoliths.
Metabolism
C. pelagicus participates in photosynthesis and is considered a phospholithoautotroph, meaning it gains its energy from the sun and gets its carbon from carbon dioxide (Taylor et al., 2007). An important molecule that it produces is calcite (Rowson et al., 2007).
Life Cycle
The life cycle of C. pelagicus consists of two main phases: the motile phase and the non-motile phase. Reproduction of the cells occur during the motile phase and occur via fission (Parke and Adams). The mother cells split into two or more daughter cells and a thick outer lining that had encased the mother cell is often shed by the daughter cells after the split. After about 5-8 weeks, the cells transition into the non-motile phase where they no longer swim around. They do not have their flagella anymore at the beginning of the phase. Because the cells do not move, they often form clusters on surfaces.
Ecology
Biogeochemical relevance
Biological Carbon Pump
Phytoplankton are predominant contributors to Earth’s photosynthetic activity and form the base of the trophic network of marine ecosystems as primary producers. Photosynthesis and chemosynthesis are the major sources of all organic carbon on Earth. Through carbon fixation, phytoplankton have a critical impact on CO2 concentration. Coccolithophores fix inorganic CO2 into particulate organic carbon (POC) and thus have an impact on the PIC/POC ratio. As organic carbon flows to the deep ocean as particles, it is mainly remineralized before it reaches the depth of 1000 meters considered necessary for sequestration (Sanders et al, 2014).
Carbonate pump
There are three main components of dissolved inorganic carbon (DIC) in seawater: a carbon dioxide-carbonic acid pool (CO2 + H2CO3) at equilibrium, carbonate (CO32-) and bicarbonate (HCO3-).
In addition to carbon fixation through photosynthesis, clalcifiers such as C. pelagicus produce CaCO3 shells that participate in fixing CO2 into (PIC). The inorganic carbon cycle participates in reducing the DIC concentration at the surface of oceans (Falkowski et al, 2000) and is a major actor in the flow of particulate carbon to the deep ocean.
The PIC to POC ratio, driven by the rates of calcification and photosynthesis, determines whether calcifiers act as a source of CO2, or a sink. The immediate consequence of calcification is a production of CO2 resulting from the assimilation of bicarbonate (HCO3-) ions. However, over longer geological periods, the effects of calcification in ocean waters are of a carbon sink.
Ocean Acidification and Warming
Carbonate and bicarbonate account for a major control of the pH of seawater through the CO2 to HCO3- and CO32- equilibrium. Calcification rate experiments suggest that impacts of seawater acidification are species-specific (Gafar et al, 2019). Thus, the structure of phytoplanktonic communities is expected to change in an acidifying ocean.
Experimental approaches have showed that high seawater temperatures increase the requirements of micro-nutrients such as phosphorus (P) and decrease the PIC/POC ratio by 40-60% (Gerecht et al, 2014). Temperature-challenged cells grew more calcite plates malformations (Gerecht et al, 2014).
Increased temperature experiments on calcification rates and growth have showed conflicting results and further research is needed to investigate the consequences of Ocean Warming on C. pelagicus.
References
[2] [Monteiro, F., Bach, L., Brownlee, C., et al. “Why Marine Phytoplankton Calcify.” Science Advances, vol. 2, no. 7, July 2016.]
[3] [McIntyre, A. and Bé, A. W. H. "Modern coccolithophoridae of the Atlantic Ocean—I. Placoliths and cyrtoliths". Deep Sea Research and Oceanographic Abstracts. 1967. Volume 14. p. 561-597.]
[4] [Baumann, K.-H., Andruleit, H., & Samtleben, C. "Coccolithophores in the Nordic Seas : Comparison of living communities with surface sediment assemblages". Deep Sea Research Part II: Topical Studies in Oceanography. 2000. Volume 47(9), p. 1743‑1772.]
[5] [Daniels, C. J. "The Biogeochemical Role of Coccolithus pelagicus". Doctoral Thesis. 2015.]
[6] [Poulton, A. J., Sanders, R., Holligan, P. M., Stinchcombe, M. C., Adey, T. R., Brown, L., & Chamberlain, K. "Phytoplankton mineralization in the tropical and subtropical Atlantic Ocean". Global Biogeochemical Cycles. 2006. Volume 20(4).]
[7] [Milliman, J. D. "Coccolithophorid production and sedimentation, Rockall Bank". Deep Sea Research Part A. Oceanographic Research Papers. 1980. Volume 27(11) p. 959‑963.]
[8] [Ziveri, P., Baumann, K., Bockel, B., Bollman, J, and Young, J. “Biogeography of Selected Holocene Coccoliths in the Atlantic Ocean.”, Springer Verlag, 2004.]
[9] [Read, B, et al. “Pan Genome of the Phytoplankton Emiliania Underpins Its Global Distribution.” Nature, vol. 499, no. 7457, 12 June 2013, pp. 209–213.]
[10] [Taylor, Alison R, et al. “Dynamics of Formation and Secretion of Heteroccoliths by Coccolithus Pelagicus Ssp. Braarudii.” European Journal of Phycology, 18 May 2007.]
[11] [Rowson, Jeremy D, et al. “Calcium Carbonate Deposition in the Motile (Crystallolithus) Phase of Coccolithus Pelagicus (Prymnesiophyceae).” British Phycological Journal, 24 Feb. 2007.]
[12] [Cachão, M, and M.T Moita. “Coccolithus Pelagicus , a Productivity Proxy Related to Moderate Fronts off Western Iberia.” Marine Micropaleontology, vol. 39, no. 1-4, 2000, pp. 131–155.]
[13] [Parke, Mary, and Irene Adams. “The Motile (Crystallolithus Hyalinus Gaarder & Markali) and Non-Motile Phases in the Life History of Coccolithus Pelagicus (Wallich) Schiller.” Journal of the Marine Biological Association of the United Kingdom, vol. 39, no. 2, 1960, pp. 263–274.]
[14] [Sanders, R., Henson, S. A., Koski, M., De La Rocha, C. L., Painter, S. C., Poulton, A. J., Riley, J., Salihoglu, B., Visser, A., Yool, A., Bellerby, R., & Martin, A. P. "The Biological Carbon Pump in the North Atlantic". Progress in Oceanography. 2014. Volume 129(PB). p. 200‑218.]
[15] [Falkowski, P., Scholes, R. J., Boyle, E., Canadell, J., Canfield, D., Elser, J., Gruber, N., Hibbard, K., Högberg, P., Linder, S., Mackenzie, F. T., Moore III, B., Pedersen, T., Rosenthal, Y., Seitzinger, S., Smetacek, V., & Steffen, W. "The Global Carbon Cycle : A Test of Our Knowledge of Earth as a System". Science. 200. Volume 290(5490). p. 291‑296.]
[16] [Gafar, N. A., Eyre, B. D., & Schulz, K. G. "Particulate inorganic to organic carbon production as a predictor for coccolithophorid sensitivity to ongoing ocean acidification". Limnology and Oceanography Letters. 2019. Volume 4(3). p. 62‑70.]
[17] [Gerecht, A. C., Šupraha, L., Edvardsen, B., Probert, I., & Henderiks, J. "High temperature decreases the PIC / POC ratio and increases phosphorus requirements in Coccolithus pelagicus (Haptophyta)". Biogeosciences. 2014. Volume 11(13), p. 3531‑3545.]
Author
Page authored by Audrey Lee, Mariah Martin, and Enora Marrec, students of Prof. Jay Lennon at IndianaUniversity.
