A review of the coccolithophorid Emiliania huxleyi (Prymnesiophyceae), with particular reference to growth, coccolith formation, and calcification-photosynthesis interactions

Abstract

E. PAASCHE. 2001. A review of the coccolithophorid Emi li ania huxleyi (Prymnesiophyceae), with particular reference to growth, coccolith formation, and calcification-photosynthesis interactions. Phycologia 40: 503-529.Emi li ania huxleyi is numerically the most important coccolithophorid in the modern ocean and has been intensely studied in the contexts of biogeochemistry (especially relating to the global carbon cycle), plankton ecology, biomineralization, and cellular carbon transport. This paper reviews older as well as more recently acquired information on reproduction, mor phology, ecophysiology, and cell physiology of E. huxleyi , emphasizing aspects that are relevant to coccolith formation and calcification-photosynthesis interactions. The existence of a number of ecotypes, which probably accounts for the wide distribution of this species in nature, complicates comparisons between laboratory studies in which different clones have been used. Coccolith formation is a strongly regulated process; use of mutants may be helpful in elucidating the control mechanisms involved. Conceptual models illustrating the role of calcification in photosynthetic carbon supply are supported by extensive experimental evidence, but the exact mechanisms of calcium and bicarbonate ion transport and of CO2 entry into the cell remain to be established.

Comparison of photosynthetic responses in diploid and haploid life-cycle phases of Emiliania huxleyi (Prymnesiophyceae)

“…Since flagella are absent in this phase, the evolution of a system for protection against the harmful effects of high irradiance represents an essential complementary aspect of the highly successful ecological strategy of this phase of the life cycle. The results of this study demonstrate an important physiological difference between diploid and haploid phases in the life cycle of Emiliania huxleyi, and we therefore stress the opinion of Paasche (2001) that it is important to state clearly which cell form was used in a given investigation. Further physiological comparisons of coccolithophore life-cycle phases are essential for developing an understanding of the total ecological strategy of these important microalgae, and for E. huxleyi there is a clear need for quantification of the spatial and temporal distribution of the non-calcifying haploid stage in the field.…”

“…The haploid S-cells could play a role in the biology of Emiliania huxleyi beyond that of serving as gametes (Paasche 2001). The results of this study provide some indications as to the possible ecology of the motile haploid phase of E. huxleyi.…”

“…The original (nonaxenic) culture of Emiliania huxleyi employed in this study (strain AC472 from the Algobank Culture Collection, Caen, France, isolated from a sample collected west of New Zealand in October 1998) was clonal, 1 cell in the coccolith-bearing phase being isolated from a plankton sample with a micropipette. This strain has been identified as E. huxleyi type R (see Paasche 2001. Following phase change in culture (i.e.…”

The influence of lithogenic material on particulate inorganic carbon measurements of coccolithophores in the Bay of Biscay

“…Coccolithophores form layers of extracellular plates of calcium carbonate (calcite) known as coccoliths, although the function of these coccoliths is not fully understood (Paasche 2002). Emiliania huxleyi is the most abundant and well-documented species of coccolithophore, widespread at subpolar latitudes and forming intensive blooms that turn surface waters a milky white (Holligan et al 1983).…”

“…Coccolithophores are of considerable interest as the production of coccolith calcite during blooms is a potentially large source of CO 2 (Paasche 2002), while export of coccoliths may have a significant role in the export of organic matter-a ''ballast effect'' (Klaas and Archer 2002). The balance of these two roles has considerable ramifications for the global carbon cycle.…”