The life cycle of Phaeocystis: state of knowledge and presumptive role in ecology

Abstract

Despite numerous investigations, the number and role of morphotypes involved in the life cycle of Phaeocystis species remain under debate. This is partly due to the application of diVerent methodologies such as light, transmission, scanning electron microscopy and Xow cytometry on speciWc samples. This heterogeneity of approaches results in the incomplete morphometric description of the diVerent cell types existing within one species according to relevant criteria and the indetermination of the ploidy level of each observed stage. We review here the diVerent morphotypes observed within each of the six Phaeocystis species recognized up to now. Four diVerent cell types have been observed. In common to all six species is the occurrence of a scaly Xagellate producing star-forming Wlaments (all species except P. jahnii) or not (P. globosa and P. jahnii). In three colony-forming species, P. globosa, P. pouchetii and P. antarctica, three morphotypes are observed: a Xagellate with scales and Wlaments, a colonial cell, and a Xagellate devoid of scales and Wlaments. In the non-colonyforming species, P. scrobiculata and P. cordata, only Xagellates with scales and Wlaments have been observed. While suspected in P. pouchetii and P. antarctica, a haploid-diploid life cycle has only been evidenced for P. globosa. The two main prominent features of this cycle are that sexuality is prevalent in colony bloom formation and termination and that two types of vegetative reproduction exist. The ecological relevance of alternating haploid and diploid stages is not clearly apparent on the basis of existing ecological studies.

Colony formation in <i>Phaeocystis antarctica</i>: connecting molecular mechanisms with iron biogeochemistry

“…The genus Phaeocystis is a cosmopolitan marine phytoplankton group that plays a key role in global carbon and sulfur cycles (Hamm et al, 1999;Matrai et al, 1995;Rousseau et al, 2007;Schoemann et al, 2005;Smith et al, 1991;Solomon et al, 2003;Thingstad and Billen, 1994;Verity et al, 2007). Because of their large cell concentrations during bloom formation, Phaeocystis have a significant impact on the ocean biogeochemistry through carbon fixation (Arrigo et al, 1999;Hamm et al, 1999;Matrai et al, 1995;Rousseau et al, 2007;Schoemann et al, 2005;Smith et al, 1991;Solomon et al, 2003;Thingstad and Billen, 1994;Verity et al, 2007), the release of large concentrations of organic carbon upon grazing and viral lysis (Alderkamp et al, 2007;Hamm et al, 1999;Lagerheim, 1896;Verity et al, 2007), and export as aggregates out of the photic zone .…”

“…Because of their large cell concentrations during bloom formation, Phaeocystis have a significant impact on the ocean biogeochemistry through carbon fixation (Arrigo et al, 1999;Hamm et al, 1999;Matrai et al, 1995;Rousseau et al, 2007;Schoemann et al, 2005;Smith et al, 1991;Solomon et al, 2003;Thingstad and Billen, 1994;Verity et al, 2007), the release of large concentrations of organic carbon upon grazing and viral lysis (Alderkamp et al, 2007;Hamm et al, 1999;Lagerheim, 1896;Verity et al, 2007), and export as aggregates out of the photic zone . Through the production of dimethylsulfide (DMS), they also directly connect ocean and atmospheric processes and carbon and sulfur cycling .…”

“…Once formed, cells typically associate with this outer layer of the colony . Colony formation involves the exudation of (muco)polysaccharides and carbohydraterich dissolved organic matter, as well as amino sugars and amino acids; it is estimated that approximately 50 %-80 % of Phaeocystis carbon is allocated to this extracellular matrix (Hamm et al, 1999;Matrai et al, 1995;Rousseau et al, 2007;Solomon et al, 2003;Thingstad and Billen, 1994). Thus, not only does the colony increase the size of Phaeocystis by several orders of magnitude, but the extracellular matrix material also constitutes the majority of measured algal (carbon) biomass (Rousseau et al, 1990).…”

Effects of elevated CO2 on phytoplankton community biomass and species composition during a spring Phaeocystis spp. bloom in the western English Channel

“…relies on composite independent investigations combining light microscopy, transmission and scanning electron microscopy as well as flow cytometry for a complete identification of the morphotype (Rousseau et al, 2007). Such an investigation was beyond the scope and resources available for this study.…”

Buoyancy Regulation in Phaeocystis globosa Scherffel Colonies

“…Colonies of Phaeocystis are surrounded by thin mucous skins, with the colonial cells distributed along the periphery and weakly interconnected by diluted gel [4,5]. The colonial form is often the dominant morphotype in a Phaeocystis bloom [6,7].…”