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Nannoplankton Coccolithophores Kingdom: Protista Division: Chrysophyta Class: Coccolithophyceae Introduction They are unicellular marine planktonic protists (algae) with photosynthetic pigments and two flagella and haptonema (whiplike organ). It is surrounded by scales (plates) called COCCOLITHS. Size: 5-60 µm, plate size = 10 µm Live coccolith cell surrounded by scales after J. Young, NHM. Coccoliths morphology Plate (coccolith) consists of shields, plates, central area with or without bars, spine, distal side (outward) and proximal side Morphological components of coccoliths Emiliana huxleyi Reticulofenestra sessilis Gephyrocapsa oceanic Some common recent coccoliths. From The Natural History Museum, London Coccolith Life-Style, Ecology and Reproduction Coccolithophores live in the photic zone (the surface waters, where sunlight reaches) and are photosynthesising (autotrophic); so are at the bottom of the marine food chain, excellent food for herbivorous bacteria. Some have flagella (whip-like appendages) so unlike plants, are capable of movement; furthermore, they don't simply float around, but can swim. Although they are photosynthesising, some have been known to eat bacteria. Reproduction is asexual-----simple division. Sensitive for temprature, more abundant at the tropics 100 000 cells/l. Coccoliths and Sedimentation After death, they sink by rate of 15 cm/day. Factors of dissolution They form high proportion of carbonate in the sediments Recent 26% Chalk (Cretaceous) 26% Eocene 90% They are largest producers of calcium carbonate on Earth today, and probably have been since the Late Jurassic. They dump about 1.5 million tons yearly of limestone to the ocean floor. Geologic history of coccoliths Abundance of coccoliths in the stratigraphic column (Brasier, 1980). Important coccoliths in the geologic history: a-b) Cyclococcolithina (OligoceneRecent), c-d) Pseudoemiliania (Pliocene-Pleistocene), e) Helicopontosphaera (Eocene-Recent), f) Zygodiscus (U. Cret-Eocene), g) Prediscosphaera (Cretaceous), h) Braarudosphaeara (Cret-Recent), j) Rhabdosphaeara (Pliocene-Recent) and k) Discoaster (Mio-Pliocene). From Brasier 1980.
