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Name derivation:

"Dusky or Dark cells" -- Dusky Phaeo- cells cystis



Phaeocystis Lagerheim 1893; 9 of 11 species descriptions are currently accepted taxonomically.

Order Phaeocystales; Family Phaeocystaceae



Alternation between pyriform biflagellate unicells 4.5 - m long with a short haptonema (Throndsen 1997), and large colonies of non-flagellated spherical cells each having two chloroplasts.


Similar genera:



Marine plankton, widely distributed. Maximum population develops in late winter and spring in New England USA. Also grows in ice, likely protected from freezing damage by producing dimethyl sulfide (DMS) that is oxidized to dimethyl sulfoxide, known to protect cells from ice damage.

During blooms Phaeocystis is responsible for development of sea foam, sometimes in massive volume, apparently as the result of proteins and lipids released with cell lysis. The disagreeable odor of DMS may accompany the blooms.

Large colonies of Phaeocystis become hosts for epiphytic diatoms (attached to the outer surface of the colonies), e.g. Pseudonitzschia poutchetii and other species. During bloom development in During April 2005 colonies decreased from ~1600 to ~200 ml-1 while increasing from 50 to 400 m diameter off western Norway (Sazhin et al. 2007).

Internal colonization may also take place (Eric Schroeder, Gulf of Maine Great Bay Watch, personal communication).

Impact on nutrient cycling:

Phaeocystis is important in global cycling of carbon and sulfur. It is responsible for ~10% of oceanic photosynthesis and emits 3-dimethylsulphoniopropionate (DMSP), precursor of dimethyl sulfide (DMS) that adds about 1.5x1013 g sulfur to the atmosphere each year, contributing to cloud formation and potentially to climate regulation (see much more at phaeocystis.org ).


Bloom death

Phaeocystis blooms can concentrate in near-shore ocean currents to more than 7*107 cells per liter. Several cases of fish kill have been reported. In the Netherlands 10 million kg of mussels were killed when the Phaeocystis cell concentration was 48 million per liter. The end of a bloom occurs when the cells (colonies) sink onto sediments and decay.  The cells apparently settled on the mussel beds and lysed, causing the mussel death, presumably by a combination of anoxia and the release of H2S and NH3 (Peperzak and Poelman 2008).



Guiry, M.D. and G.M. Guiry 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 30 April 2013.

Lagerheim, G. 1896. Phaeocystis nov. gen., grundadt p Tetraspora Poucheti Har. Botaniska Notiser 1893:32-33.

Peperzak, L., and M. Poelman 2008. Mass mussel mortality in The Netherlands after a bloom of Phaeocystis globosa (prymnesiophyceae). Journal of Sea Research 60:220-222.

Sazhin, A., L. F. Artigas, J.C. Nejstgaard, and M.E. Frischer 2007. The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass. Biogeochemistry 83:137-145.

Throndsen, J. 1997. The planktonic marine flagellates. In: Identifying marine phytoplankton. Tomas, C.R. (Ed.).