Coccolithus pelagicus

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Classification

Domain; Phylum; Class; Order; family [Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Genus species

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 (Nishida, 1979). 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, 2007) 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

Interesting features of cell structure; how it gains energy; what important molecules it produces. BoldCell Structure The Coccolithus 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.). 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.

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 (CO₃^2-) 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, ) 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 CO₃^2- 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

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.

Ziveri, P., Baumann, K., Bockel, B., Bollman, J, and Young, J. “Biogeography of Selected Holocene Coccoliths in the Atlantic Ocean.” ResearchGate, Springer Verlag, 2004.

Monteiro, F., Bach, L., Brownlee, C., et al. “Why Marine Phytoplankton Calcify.” Science Advances, vol. 2, no. 7, July 2016.

[www.nature.com/articles/nature12221, 10.1038/nature12221 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.]

Author

Page authored by Audrey Lee, Mariah Martin, and Enora Marrec, students of Prof. Jay Lennon at IndianaUniversity.