G. Karst. (Karsten, 1905:130, pl. 18, fig. 16)
Kornmann (1955: 220, figs 1-6), Kayser (1970: 195), Richardson & Whitaker (1979: 110), Chang (1984: 306, figs 1-7), Davidson & Marchant (1992b: 5, figs 1b, c, 2, 3), Marchant & Thomsen (1994: 211), Medlin et al. (1994: 207)
Life Cycle: Phaeocystis has a complex life cycle including haploid microzoo-spores, macrozoospores and non-motile cells. The two life cycle stages commonly observed are biflagellate motile cells and palmelloid colonial cells. However, non-motile cells have been described for other members of the genus (Kornmann, 1955; Kayser, 1970; Cariou et al., 1994). Motile cells: Cells solitary, biflagellate and with a haptonema, spherical to ovoid, 5-8 µm diameter. Flagella equal, 8-12 µm long, bearing hair-points. Haptonema short, stiff, with a bulbous tip, arising between the flagella but in a different plane from the flagellar bases. Cell body with 2 layers of organic scales; scales of outer layer usually almost circular, 0.18 × 0.19 µm, to 0.19 × 0.27 µm diameter (Hallegraeff, 1983; Marchant & Davidson, unpublished data), flat, with a perpendicular outwardly raised rim, usually with 45-48 ridges radiating from a rectangular unornamented centre on both surfaces. Scales of inner layer with a strongly inflexed rim, oval, 0.10 × 0.13 µm diameter, with 30 ridges radiating from an oval unornamented centre on both surfaces. Motile cells also release 'star' arrays. Threads of these arrays are 20-100 µm long (Buck & Garrison, 1983; Fryxell, 1989), composed of single or overlapping segments and tapering distally. Proximal ends of the threads overlap to form a membrane-bound pentagon. Colonial cells: Colonies commonly spherical, from c. 10 µm diameter (containing only a few cells) to 2 cm diameter (containing thousands of cells), comprising a mucilaginous matrix with the cells arranged randomly around the periphery of the matrix. Cells spherical, 5-10 µm diameter, lacking body scales, haptonema and flagella. Other motile morphs: Ultrastructural studies indicate that there are at least two Phaeocystis-like algae in Antarctic waters that are difficult to distinguish (Marchant & Davidson, unpublished data). The three scale morphologies, all with distinct rims (see, table), differ from the foregoing description of P. antarctica.
Phaeocystis pouchetti-like, lobed colonies with clumped cell distributions or cells aggregated at one pole have also been observed in Antarctic waters (Marchant, unpublished data).
Circumpolar (Hart, 1942); Weddell Sea (Baumann et al., 1994); Prydz Bay, East Antarctica (Davidson & Marchant, 1987); coastal waters off Davis Station, East Antarctica (Davidson & Marchant, 1992); Ross Sea (DiTullio et al., 2000)); type locality, Antarctic Ocean, "Challenger" Expedition (Karsten, 1905); Bransfield Strait (Kang & Lee, 1995).
Phaeocystis antarctica was genetically differentiated as a distinct species by Medlin et al. (1994) and is the only Phaeocystis species currently recognised from Antarctic waters. However, no definitive characterisation of its morphology has been published. EM studies (Davidson & Marchant, unpublished data) indicate a strong similarity with descriptions of the flagellate stage of P. pouchetii (Har.) Lagerh. (Parke et al., 1971), while the life cycle and colony morphology resemble P. globosa Scherff. (Baumann et al., 1994; Rousseau et al., 1994). An additional, non-motile cell stage has been observed in cultured material (Kornmann, 1955; Kayser, 1970). Kornmann (1955) described the formation of non-motile cells from flagellate cells, which in turn formed colonies. In contrast, Kayser (1970) reported that the non-motile cells became attached to solid surfaces and released new, free, single cells and colonies into the water column. These non-motile, single cells were proposed as being benthic in nature or attached to particles. Whether or not both authors referred to the same cell type is uncertain.Phaeocystis antarctica is among the most abundant of Antarctic phytoplankton species. Cell concentrations can reach 6 × 10^7 cells per litre, giving the sea a brownish, oily appearance and releasing sufficient quantities of dimethylsulphide (DMS) to produce a pungent smell. It is one of the first algae to bloom in coastal Antarctica where it frequently dominates the phytoplankton in the ice and in ice-edge waters during spring (Fryxell et al., 1984; Perrin et al., 1987; Garrison & Buck, 1989).