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[1] Carbonates are the largest reservoirs of carbon on Earth. From mid-Mesozoic time, the biologically catalyzed precipitation of calcium carbonates by pelagic phytoplankton has been primarily due to the production of calcite by coccolithophorids. In this paper we address the physical and chemical processes that select for coccolithophorid blooms detected in Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color imagery. Our primary goal is to develop both diagnostic and prognostic models that represent the spatial and temporal dynamics of coccolithophorid blooms in order to improve our knowledge of the role of these organisms in mediating fluxes of carbon between the ocean, the atmosphere, and the lithosphere. On the basis of monthly composite images of classified coccolithophorid blooms and global climatological maps of physical variables and nutrient fields, we developed a probability density function that accounts for the physical chemical variables that predict the spatiotemporal distribution of coccolithophorids in the world oceans. Our analysis revealed that areas with sea surface temperatures (SST) between 3°and 15°C, a critical irradiance between 25 and 150 mmol quanta m À2 s À1 , and decreasing nitrate concentrations (DN/Dt < 0) are selective for upper ocean large-scale coccolithophorid blooms. While these conditions favor both Northern and Southern Hemisphere blooms of the most abundant coccolithophorid in the modern oceans, Emiliania huxleyi, the Northern and Southern Hemisphere populations of this organism are genetically distinct. Applying amplified fragment length polymorphism as a marker of genetic diversity, we identified two major taxonomic clades of E. huxleyi; one is associated with the Northern Hemisphere blooms, while the other is found in the Southern Hemisphere. We suggest a rule of ''universal distribution and local selection'': that is, coccolithophorids can be considered cosmopolitan taxa, but their genetic plasticity provides physiological accommodation to local environmental selection pressure. Sea surface temperature, critical irradiance, and DN/Dt were predicted for the years 2060-2070 using the NCAR Community Climate System Model to generate future monthly probability distributions of coccolithophorids based upon the relationships observed between the environmental variables and coccolithophorid blooms in modern oceans. Our projected probability distribution analysis suggests that in the North Atlantic, the largest habitat for coccolithophorids on Earth, the areal extent of blooms will decrease by up to 50% by the middle of this century. We discuss how the magnitude of carbon fluxes may be affected by the evolutionary success of coccolithophorids in future climate scenarios.

A phylogenomic approach was used to study the evolution of traits in the Cyanobacteria. A cyanobacterial backbone tree was constructed using multiple concatenated sequences from whole genome sequences. Additional taxa were added using a separate alignment that contained morphological characters, SSU (small subunit) and LSU (large subunit) rDNA, rpoC, rpoD, tufA, and gyrB genes. A compartmentalization approach was then used to construct a robust phylogeny with resolved deep branches. Additional morphological characters (e.g. unicellular or filamentous growth, presence or absence of heterocysts) were coded, mapped onto the backbone cyanobacterial tree, and the ancestral character states inferred. Our analyses show that the earliest cyanobacterial lineages were likely unicellular coccoid/ellipsoidal/short rods that lived in terrestrial/freshwater environments. Later cyanobacterial lineages independently gained the ability to colonize brackish, marine, and hypersaline environments while acquiring a large number of more complex traits: sheath, filamentous growth, nitrogen fixation, thermophily, motility, and use of sulphide as an electron donor. Many of these adaptations would have been important in the appearance of dense microbial mats early in Earth's history. Complex traits such as hormogonia, heterocysts, and akinetes had a single ancestor. Within the Nostocales, hormogonia and heterocysts arose before akinetes.

) shows that strains of the GV3 genotype produce gas vesicles with a higher critical pressure than those of GV1 and GV2. A PCR survey of 185 clonal cultures of P. rubescens isolated from Lake Zu $ rich revealed that 3 isolates were of genotype GV1, 73 were of GV2 and 109 were of GV3. The PCR technique was used to distinguish the gas vesicle genotype, and thence the associated critical-pressure phenotype, of single filaments selected from lakewater samples. Sequence analysis of the 16S rDNA and of regions within the operons encoding phycoerythrin, phycocyanin and Rubisco confirmed that these strains of Planktothrix form a tight phylogenetic group.

SUMMARYObservations were made on the vertical distribution of colonies of Aphanizomenon fios-aquae for 9 d at a driftstation east of Bornholm Island in the Baltic Sea. The buoyant colonies were dispersed in the upper layers of the water column during periods of wind-induced mixing but floated up during calm periods. From measurements of the vertical light extinction, surface irradiance and the photosynthesis versus irradiance curve, calculations were made of the changes in the daily integral of photosynthesis with respect to time and depth throughout the water column. From these calculations it is demonstrated that net photosynthesis by the population of Aphanizomenon fios-aquae increased nearly threefold by floating up after a deep mixing event. It is estimated that, averaged over alternating periods of calm and mixing, the buoyancy provided by gas vesicles in this organism will result in a nearly twofold increase in photosynthesis. A quantitative analysis has been made of the relationship of the daily integral of photosynthesis by the Aphanizomenon population with the mean depth of the population in the water column and the daily insolation. The analysis shows that the integral decreases linearly with respect to mean depth.

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Using primer pairs for seven previously described microsatellite loci and three newly characterized microsatellite loci from the coccolithophore Emiliania huxleyi (Lohm.) Hay and Mohler, we assessed genetic variation within this species. Analysis of microsatellite length variants (alleles) was conducted for 85 E. huxleyi isolates representative of different ocean basins. These results revealed high intraspecific genetic variability within the E. huxleyi species concept. Pairwise comparison of a 1992 Coastal Fjord group (FJ92) (n 5 41) and a North East Atlantic (NEA) group (n 5 21), using F ST as an indicator of genetic differentiation, revealed moderate genetic differentiation (F ST 5 0.09894; P 5 0; significance level 5 0.05). Gene flow between the FJ92 and NEA groups was estimated to be low, which is in agreement with the moderate levels of genetic differentiation revealed by the microsatellite data. A genetic assignment method that uses genotype likelihoods to draw inference about the groups to which individuals belong was tested. Using FJ92 and NEA as reference groups, we observed that all the E. huxleyi groups tested against the two reference groups were unrelated to them. On a global biogeographical scale, E. huxleyi populations appear to be highly genetically diverse. Our findings raise the question of whether such a high degree of intraspecific genetic diversity in coccolithophores translates into variability in ecological function.