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.

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The objectives of this study were to determine rDNA sequences of the most common Dinophysis species in Scandinavian waters and to resolve their phylogenetic relationships within the genus and to other dinoflagellates. A third aim was to examine the intraspecific variation in D. acuminata and D. norvegica, because these two species are highly variable in both morphology and toxicity. We obtained nucleotide sequences of coding (small subunit [SSU], partial large subunit [LSU], 5.8S) and noncoding (internal transcribed spacer [ITS]1, ITS2) parts of the rRNA operon by PCR amplification of one or two Dinophysis cells isolated from natural water samples. The three photosynthetic species D. acuminata, D. acuta, and D. norvegica differed in only 5 to 8 of 1802 base pairs (bp) within the SSU rRNA gene. The nonphotosynthetic D. rotundata (synonym Phalacroma rotundatum[Claparède et Lachmann] Kofoid et Michener), however, differed in approximately 55 bp compared with the three photosynthetic species. In the D1 and D2 domains of LSU rDNA, the phototrophic species differed among themselves by 3 to 12 of 733 bp, whereas they differed from D. rotundata by more than 100 bp. This supports the distinction between Dinophysis and Phalacroma. In the phylogenetic analyses based on SSU rDNA, all Dinophysis species were grouped into a common clade in which D. rotundata diverged first. The results indicate an early divergence of Dinophysis within the Dinophyta. The LSU phylogenetic analyses, including 4 new and 11 Dinophysis sequences from EMBL, identified two major clades within the phototrophic species. Little or no intraspecific genetic variation was found in the ITS1–ITS2 region of single cells of D. norvegica and D. acuminata from Norway, but the delineation between these two species was not always clear.

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The silicon content of five species of marine planktonic diatoms grown in laboratory culture was measured by a method involving soda hydrolysis of cells collected on polycarbonate filters. An increase in the temperature or light intensity during growth resulted in an increase in the Si content in some species and a decrease in others. The magnitude of these changes depended on whether the results were expressed as pg Siacell-r, pg Si*prnd2 cell surface area, or pg Si per pg C.