''Phaeocystis'' is a genus of algae belonging to the
Prymnesiophyte class and to the larger division of
Haptophyta
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...
.
It is a widespread marine
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and can function at a wide range of temperatures (
eurytherm
A eurytherm is an organism, often an endotherm, that can function at a wide range of ambient temperatures. To be considered a eurytherm, all stages of an organism's life cycle must be considered, including juvenile and larval stages. These wide ...
al) and salinities (
euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly (''Poecilia sphenops'') which can live in fresh water, brackish water, or salt water.
The green crab (''Carcinus maenas'') is an e ...
).
Members of this genus live in the open ocean, as well as in sea ice.
It has a polymorphic life cycle, ranging from free-living cells to large colonies.
The ability to form a floating colony is one of the unique attributes of ''Phaeocystis'' – hundreds of cells are embedded in a polysaccharide gel matrix, which can increase massively in size during
blooms.
The largest ''Phaeocystis'' blooms form in the polar seas: ''P. pouchetii'' in the north and ''P. antarctica'' in the south.
This intense ''Phaeocystis'' productivity generally persists for about a three-month period, spanning most of the summer in the Southern Hemisphere. ''Phaeocystis''-abundant ecosystems are generally associated with commercially important stocks of crustaceans, molluscs, fish and mammals. ''Phaeocystis'' may have negative effects on higher trophic levels in the marine ecosystem, and consequent impacts on human activities (such as fish farming and coastal tourism), by forming odorous foams on beaches during the wane of a bloom.
The ability to form large blooms and its ubiquity make ''Phaeocystis'' an important contributor to the ocean
carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
. In addition, ''Phaeocystis'' produces
dimethyl sulfide (DMS), a key player in the
sulfur cycle.
Distribution and life cycle
![Phaeocystis](https://upload.wikimedia.org/wikipedia/commons/a/a3/Phaeocystis.png)
Free-living forms of ''Phaeocystis'' are globally distributed and occur in a variety of marine habitats, including coastal oceans, open oceans, polar seas and sea ice.
Seven species are currently assigned to the genus: ''P. antarctica'', ''P. jahnii'', ''P. globosa'', ''P. pouchetti'', ''P. scrobiculata'' (not in culture), ''P. cordata,'' and ''P. rex''.
Three species (''P. globosa'', ''P. pouchetii'', and ''P. antarctica'') are associated with bloom formation in nutrient-rich areas, which can occur either naturally (e.g. in the
Ross Sea
The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who ...
,
Greenland Sea or the
Barents Sea
The Barents Sea ( , also ; no, Barentshavet, ; russian: Баренцево море, Barentsevo More) is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and divided between Norwegian and Russian territo ...
) or due to anthropogenic inputs (e.g. in the Southern Bight of the
North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
or the
Persian Gulf
The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
). Generally, ''P. globosa'' blooms in temperate and tropical waters, whereas ''P. pouchetii'' and ''P. antarctica'' are better adjusted to the cold temperatures prevailing in Arctic and Antarctic waters, respectively. However, ''P. pouchetii'' also tolerates warmer temperatures and has been seen in temperate waters.
Genome comparison has shown that the
RUBISCO
Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is con ...
spacer region (located in the
plastid DNA, between two subunits of the enzyme 1,5 -bisphosphate carboxylase) is highly conserved among closely related colonial ''Phaeocystis'' species and identical in ''P. antarctica'', ''P. pouchetii'' and two warm-temperate strains of ''P. globosa'', with a single base substitution in two cold-temperate strains of ''P. globosa''.
''Phaeocystis'' can exist as either free-living cells or colonies. Free-living cells can show a variety of morphologies, depending on the species. All species can exist as scaled
flagellates, and this is the only form that has been observed for ''P. scrobiculata'' and ''P. cordata''. Three species have been observed as colonies (''P. globosa'', ''P. pouchetii'' and ''P. antarctica'') and these can also exist as a flagellate devoid of scales and filaments.
In colonies of ''Phaeocystis'', the colony skin may provide protection against smaller zooplankton grazers and viruses.
While suspected in other species (''P. pouchetii'' and ''P. antarctica''), a haploid-diploid life cycle has only been observed in ''P. globosa''. In this cycle,
sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
is dominant in colony bloom formation/termination, and two types of
vegetative reproduction
Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...
exist.
Impacts on global ocean
The genus ''Phaeocystis'' is a major producer of 3-dimethylsulphoniopropionate (DMSP), the precursor of dimethyl sulfide (DMS). Biogenic DMS contributes approximately 1.5×10
13 g sulfur to the atmosphere annually and plays a major part in the global sulfur cycle, which can affect cloud formation and, potentially, climate regulation.
Symbiosis
''Phaeocystis'' species are endosymbionts to
acantharian
The Acantharea (Acantharia) are a group of radiolarian protozoa, distinguished mainly by their strontium sulfate skeletons. Acantharians are heterotrophic marine microplankton that range in size from about 200 microns in diameter up to several ...
radiolarians.
Acantharians collected in different ocean basins host different species of ''Phaeocystis'' has their dominant symbionts: ''P. antarctica'' is found as the primary symbiont to acantharians in the Southern Ocean and ''P. cordata'' and ''P. jahnii'' are among the dominant symbionts found in acantharians collected in warm oligotrophic regions of the Indian and Pacific oceans.
In addition to the described ''Phaeocystis'' species, sequences belonging to the molecular clade Phaeo02 often make up a majority of symbiotic sequences recovered from acantharians in warm-water regions.
Whether or not this symbiosis represents a true mutualism with both partners benefiting, is debated.
Extreme cellular remodeling is observed in symbiotic ''Phaeocystis'', including a drastic increase in chloroplast number and an enlarged central vacuole.
This phenotypic change is probably induced by the host to increase photosynthetic output by symbionts, but if it renders symbiotic cells incapable of future cell-division, the symbiosis is a dead end for ''Phaeocystis''.
The symbiosis is ecologically relevant because it creates primary production hot spots in low-nutrient regions,
but it remains to be determined how the symbiosis has affected ''Phaeocystis'' evolution.
References
{{Taxonbar, from=Q3377945
Haptophyte genera