Phaeocystis

The Phaeocystis genes belong to the prymnesiophytes and to the larger division of Haptophyta (The haptophytes are classified as chromist algae, branched from red algae). This eurythermal and euryhaline genus Phaocystis is the widespread marine phytoplankton. (e.g. V. Schoemann et al. 2005). Delegate (Representative) of this genus live in the open ocean as well as in sea ice.( Welcome to the Phaeocystis antarctica genome sequencing project homepage). It has a polymorphic life cycle from free-living cells to colonies. (e.g. V. Schoemann et al. 2005). The ability to form a floating colony is one of the unique attributes of Phaeocystis with hundreds of cells embedded in a polysaccharide gel matrix that can increase massively during blooms. .( Welcome to the Phaeocystis antarctica genome sequencing project homepage). The high productivity related to its massively blooms and its ubiquity makes Phaeocystis an important contributor to the ocean carbon cycle (e.g. Smith et al., 1991; DiTullio et al., 2000). In addition, Phaeocystis produces dimethylsulfoniopropionate (DMSP) and changes it enzymatically into dimethylsulfide (DMS) and acrylate (Stefels and Van Boekel, 1993; Stefels et al., 1995).

The largest Phaeocystis blooms are from the Northern and Southern Polar seas where P. pouchetii (usually in Northern) and P. antarctica (usually in Southern) bloom.( http://www.phaeocystis.org/about.html#genus). )

This intense Phaeocystis productivity generally persists for about a three month period, spanning most of the austral summer.

Phaeocystis-abundant ecosystems are generally associated with commercially important stocks of crustaceans, molluscs, fishes and mammals. Phaeocystis might have negative effects on higher trophic levels in the marine ecosystem and consequently impact on human activities such as fisheries and fish farming, and also coastal tourism through the odorous foams on beaches during the wane of a bloom (Lancelot et al., 1987).

Distribution and species with life cycle

The genus Phaeocystis is a world-wide haptophyta and occurs as different species in various marine systems (coastal ocean/ open ocean/ polar sea/ sea ice and so on). Cells in free-living forms are global (cosmopolitan) in distribution.(e.g. Thomsen et al., 1994). This genus Phaeocystis has six different species. – P. antarctica/ P. jahnii/ P. globosa/ P. pouchetii/ P. scrobiculata/ P. cordata. Among these species, three of them (P. globose, P. pouchetii, P. Antarctica) generally produce blooms under the colony form in major nutrient-enriched areas (Lancelot et al., 1998) either naturally (e.g. Ross Sea, Greenland Sea; Barents Sea) or due to anthropogenic inputs (e.g. Southern Bight of the North Sea; Arabian Gulf). The general trend is that 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, the temperature tolerance range of P. pouchetii duplicates with that of P. globosa (Baumann et al., 1994) such that P. pouchetii is sometimes presented in temperate waters (Philippart et al., 2000). It is supported by this result that RUBISCO spacer regions are highly conserved among closely related colonial Phaeocystis species and are identical in Phaeocystis antarctica, Phaeocystis pouchetii and two warm-temperate strains of Phaeocystis globosa, with a single base substitution in two cold-temperate strains of P. globose. (M. Lange et al., 2002) In the genus of Phaeocystis has free-living cell types and colonial matrix types. The colony skin apparently provides protection against smaller zooplankton grazers and perhaps viruses. (P. G. Verity et al., 2007). In all six species, the common cell type is the scaly flagellate producing star-forming filaments (all species except P. jahnii) or not (P. globosa and P. jahnii). In general three colony-forming species, P. globosa, P. pouchetii and P. antarctica, three morphotypes are observed: 1)a flagellate with scales and filaments, 2)a colonial cell, and 3)a flagellate devoid of scales and filaments. In contrast, in the non-colony-forming species, P. scrobiculata and P. cordata, only flagellates with scales and filaments have been confirmed. While suspected in other species (P. pouchetii and P. Antarctica), a haploid-diploid life cycle has only been observed in P. globosa. The two main prominent features of this haploid-diploid life cycle are that sexuality is dominant in colony bloom formation and termination, and that two types of vegetative reproduction exist. (e.g. V. Schoemann et al. 2007).

Impacts on global ocean

The role of Phaeocystis in global carbon cycling

The Phaeocystis genus is word-wide phytoplankton. Thus, they contribute about 10% of annual global marine primary production, equivalent to 4 billion metric tons of carbon annually. Given that up to 50% of this carbon is in the form of polysaccharide gels (made by colonial cell type), 2 billion tons of polysaccharide gels is produced by Phaeocystis sp. each year. The polymer gels are dispersed into the dissolved organic carbon (DOC) pool, serve as attachment places for bacteria and protists, and sediment into the deep ocean, affecting the cycling of organic matter. Therefore, the Phaeocystis genus could play a significant role in Biological pump and Global warming/hiatus. Because DOC constitutes a large carbon pool (700 x 1015 g C) of similar magnitude to the atmospheric CO2 pool (750 x 1015 g C), understanding the cycling and reactivity of its various components and sources has implications for the global carbon cycle and carbon sequestration.

The role of Phaeocystis in global sulfur cycling

The Phaeocystis genus is a major provider of 3-dimethylsulphoniopropionate (DMSP), the precursor of dimethyl sulfide (DMS). Biogenic DMS contributes about 1.5x1013 g sulfur to the atmosphere annually and plays a major part in the global sulfur cycle, which can impact on cloud formation, and potentially in climate regulation.