A new centrohelid heliozoan, Pterocystis polycristalepis sp. nov., and taxonomic and phylogenetic concerns within Pterista (Haptista: Centroplasthelida).

A new species of centrohelid heliozoans, Pterocystis polycristalepis sp. nov. (Pterocystidae), was examined using light and electron microscopy. The novel centrohelid is characterized by the presence of leaf-like spine-scales with a broad pedicel-like structure on the proximal part and many subparallel ribs on the lateral wing surface. The plate-scales are ovoid with medial tubular thickening and many subparallel ribs on the very extensive marginal rim. The closely related species Pterocystis striata has also been studied in detail using light and electron microscopy. Phylogenetic analysis of 18S rRNA gene sequences placed both species into a separate clade within Pterista. The closest morphologically characterized species to the new clade is Triangulopteris lacunata. The 18S rRNA sequence of Pseudoraphidiophrys veliformis was grouped within Pterista and found to be closely related to Pterocystis polycristalepis, Pterocystis striata, and Triangulopteris lacunata. Cyst-scales of various shapes, cell and cyst aggregations, syncytia, and a cell with a stalk were revealed in a clonal culture of P. veliformis. Analysis of the morphology and phylogenetic position of the studied species and other centrohelids revealed a large number of taxonomic and phylogenetic problems in Pterista.

Single-cell genomics of a bloom-forming phytoplankton species reveals population genetic structure across continents.

The study of microbial diversity over time and space is fundamental to the understanding of their ecology and evolution. The underlying processes driving these patterns are not fully resolved but can be studied using population genetic approaches. Here we investigated the population genetic structure of Gonyostomum semen, a bloom-forming phytoplankton species, across two continents. The species appears to be expanding in Europe, whereas similar trends are not observed in the USA. Our aim was to investigate if populations of Gonyostomum semen in Europe and in the USA are genetically differentiated, if there is population genetic structure within the continents, and what the potential drivers of differentiation are. To this end, we used a novel method based on single-amplified genomes combined with Restriction-site Associated DNA sequencing that allows de novo genotyping of natural single-cell isolates without the need for culturing. We amplified over 900 single-cell genomes from 25 lake populations across Europe and the USA and identified two distinct population clusters, one in Europe and another in the USA. Low genetic diversity in European populations supports the hypothesized recent expansion of Gonyostomum semen on this continent. Geographic population structure within each continent was associated with differences in environmental variables that may have led to ecological divergence of population clusters. Overall, our results show that single-amplified genomes combined with Restriction-site Associated DNA sequencing can be used to analyze microalgal population structure and differentiation based on single-cell isolates from natural, uncultured samples.

Inelastic hyperspectral Scheimpflug lidar for microalgae classification and quantification.

An inelastic hyperspectral Scheimpflug lidar system was developed for microalgae classification and quantification. The correction for the refraction at the air-glass-water interface was established, making our system suitable for aquatic environments. The fluorescence spectrum of microalgae was extracted by principal component analysis, and seven species of microalgae from different phyla have been classified. It was verified that when the cell density of Phaeocystis globosa was in the range of ${{1}}{{{0}}^4}\sim{{1}}{{{0}}^6}\;{\rm{cell}}\;{\rm{m}}{{\rm{L}}^{- 1}}$, the cell density had a linear relationship with the fluorescence intensity. The experimental results show our system can identify and quantify microalgae, with application prospects for microalgae monitoring in the field environment and early warning of red tides or algal blooms.

Differences in the Formation Mechanism of Giant Colonies in Two Phaeocystis globosa Strains.

Phaeocystis globosa has become one of the primary causes of harmful algal bloom in coastal areas of southern China in recent years, and it poses a serious threat to the marine environment and other activities depending upon on it (e.g., aquaculture, cooling system of power plants), especially in the Beibu Gulf. We found colonies of P. globosa collected form Guangxi (China) were much larger than those obtained from Shantou cultured in lab. To better understand the causes of giant colonies formation, colonial cells collected from P. globosa GX strain (GX-C) and ST strain (ST-C) were separated by filtration. Morphological observations, phylogenetic analyses, rapid light-response curves, fatty acid profiling and transcriptome analyses of two type cells were performed in the laboratory. Although no differences in morphology and 18S rRNA sequences of these cells were observed, the colonies of GX strain (4.7 mm) are 30 times larger than those produced by the ST strain (300 µm). The rapid light-response curve of GX-C was greater than that of ST-C, consistent with the upregulated photosynthetic system, while the fatty acid content of GX-C was lower than that of ST-C, also consistent with the downregulated synthesis of fatty acids and the upregulated degradation of fatty acids. In summary, the increased energy generated by GX-C is allocated to promote the secretion of extracellular polysaccharides for colony formation. We performed a physiological and molecular assessment of the differences between the GX-C and ST-C strains, providing insights into the mechanisms of giant colonies formation in P. globosa.

Multi-genomic analysis of the cation diffusion facilitator transporters from algae.

Metal transport processes are relatively poorly understood in algae in comparison to higher plants and other eukaryotes. A screen of genomes from 33 taxonomically diverse algal species was conducted to identify members of the Cation Diffusion Facilitator (CDF) family of metal ion transporter. All algal genomes contained at least one CDF gene with four species having >10 CDF genes (median of 5 genes per genome), further confirming that this is a ubiquitous gene family. Phylogenetic analysis suggested a CDF gene organisation of five groups, which includes Zn-CDF, Fe/Zn-CDF and Mn-CDF groups, consistent with previous phylogenetic analyses, and two functionally undefined groups. One of these undefined groups was algal specific although excluded chlorophyte and rhodophyte sequences. The majority of sequences (22 out of 26 sequences) from this group had a putative ion binding site motif within transmembrane domain 2 and 5 that was distinct from other CDF proteins, such that alanine or serine replaced the conserved histidine residue. The phylogenetic grouping was supported by sequence cluster analysis. Yeast heterologous expression of CDF proteins from Chlamydomonas reinhardtii indicated Zn2+ and Co2+ transport function by CrMTP1, and Mn2+ transport function by CrMTP2, CrMTP3 and CrMTP4, which validated the phylogenetic prediction. However, the Mn-CDF protein CrMTP3 was also able to provide zinc and cobalt tolerance to the Zn- and Co-sensitive zrc1 cot1 yeast strain. There is wide diversity of CDF transporters within the algae lineage, and some of these genes may be attractive targets for future applications of metal content engineering in plants or microorganisms.

Transcriptional patterns of Emiliania huxleyi in the North Pacific Subtropical Gyre reveal the daily rhythms of its metabolic potential.

Emiliania huxleyi is a calcifying haptophyte, contributing to both the organic and inorganic marine carbon cycles. In marine ecosystems, light is a major driver of phytoplankton physiology and ultimately carbon flow through the ecosystem. Here, we analysed a Lagrangian time-series of metatranscriptomes collected in the North Pacific Subtropical Gyre (NPSG) to examine how in situ populations of E. huxleyi modulate gene expression over day-night transitions. Many E. huxleyi contigs had a diel expression pattern, with 61% of contigs clustering into modules with statistically significant diel periodicity. Contigs involved in processes that build up energy stores, like carbon fixation and lipid synthesis, peaked around dawn. In contrast, contigs involved in processes that released energy stores, like respiration and lipid degradation, peaked mid-day and towards dusk. These patterns suggest an orchestrated cycle of building, then consuming energy stores in E. huxleyi populations in the NPSG. Selected contigs related to the cell cycle also exhibited significant diel periodicity consistent with phased modulations of division observed in culture. Overall, these patterns of gene expression suggest a daily metabolic cascade that could contribute to both organic and inorganic carbon flow in this nutrient depleted ecosystem.

Repeated species radiations in the recent evolution of the key marine phytoplankton lineage Gephyrocapsa.

Phytoplankton account for nearly half of global primary productivity and strongly affect the global carbon cycle, yet little is known about the forces that drive the evolution of these keystone microscopic organisms. Here we combine morphometric data from the fossil record of the ubiquitous coccolithophore genus Gephyrocapsa with genomic analyses of extant species to assess the genetic processes underlying Pleistocene palaeontological patterns. We demonstrate that all modern diversity in Gephyrocapsa (including Emiliania huxleyi) originated in a rapid species radiation during the last 0.6 Ma, coincident with the latest of the three pulses of Gephyrocapsa diversification and extinction documented in the fossil record. Our evolutionary genetic analyses indicate that new species in this genus have formed in sympatry or parapatry, with occasional hybridisation between species. This sheds light on the mode of speciation during evolutionary radiation of marine phytoplankton and provides a model of how new plankton species form.

Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for alkenone production.

Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long-chain ketones that are commonly used for paleotemperature reconstructions. Alkenone-producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri-unsaturated alkenone isomers (C37:3b Me, C38:3b Et, C38:3b Me, C39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small-subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high-throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well-supported clade separating the previously described "EV" clade from the "Greenland" clade. We infer the first partial large-subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well-supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri-unsaturated alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on alkenone biosynthesis.

Distribution of living coccolithophores in eastern Indian Ocean during spring intermonsoon.

We studied the biodiversity of autotrophic calcareous coccolithophore assemblages at 30 locations in the Eastern Equatorial Indian Ocean (EEIO) (80°-94°E, 6°N-5°S) and evaluated the importance of regional hydrology. We documented 26 species based on the identification of coccospheres and coccoliths, respectively. The coccolithophore community was dominated by Gephyrocapsa oceanica, Emiliania huxleyi, Florisphaera profunda, Umbilicosphaera sibogae, and Helicosphaera carteri. The abundance of coccoliths and coccospheres ranged from 0.2 × 103 to 160 × 103 coccoliths l-1 and 0.2 × 103 to 68 × 103 cells l-1, averaged 23 × 103 coccoliths l-1 and 9.4 × 103 cells l-1, respectively. Biogenic PIC, POC, and rain ratio mean values were 0.50 µgC l-1, 1.047 µgC l-1, and 0.10 respectively. High abundances of both coccoliths and coccospheres in the surface ocean layer occurred on the north of the equator. Vertically, the great majority of coccoliths and coccospheres were concentrated in water taken from depths of <75 m. The ratios between the number of coccospheres and free coccoliths indicated that coccoliths experience different levels of dissolution when transported to deep water. Abundant coccolithophores mainly occurred at the west of 90°E, which is in accordance with the presence of Wyrtki jets. Patterns of coccolithosphores and of coccoliths have been reflected in hydrological processes.

Contrasting biogeography and diversity patterns between diatoms and haptophytes in the central Pacific Ocean.

Diatoms and haptophytes are two major phytoplankton groups, playing pivotal roles in global biogeochemical cycles and marine ecosystems. In general, diatoms have higher growth rates than haptophytes, whereas haptophytes tend to have higher nutrient uptake affinity. However, precise linkages between their ecological traits and geographical distributions remain poorly understood. Herein, we examined the basin-scale variability of the abundance and taxonomic composition of these two phytoplankton groups across 35 sites in the Pacific Ocean using DNA metabarcoding. The diatom community was generally dominated by a few genera at each sample site, whereas the haptophyte community consisted of a large number of genera in most of the sites. The coexistence of various haptophyte genera might be achieved by diversification of their ecophysiological traits such as mixotrophy. On the other hand, the diatom community might experience greater inter-genus competition due to the rapid uptake of nutrients. Our data further supports the notion that their distinct ecological strategies underlie the emergence of contrasting diversity patterns of these phytoplankton groups in the central Pacific at a basin scale.

Temperature effects on sinking velocity of different Emiliania huxleyi strains.

The sinking properties of three strains of Emiliania huxleyi in response to temperature changes were examined. We used a recently proposed approach to calculate sinking velocities from coccosphere architecture, which has the advantage to be applicable not only to culture samples, but also to field samples including fossil material. Our data show that temperature in the sub-optimal range impacts sinking velocity of E. huxleyi. This response is widespread among strains isolated in different locations and moreover comparatively predictable, as indicated by the similar slopes of the linear regressions. Sinking velocity was positively correlated to temperature as well as individual cell PIC/POC over the sub-optimum to optimum temperature range in all strains. In the context of climate change our data point to an important influence of global warming on sinking velocities. It has recently been shown that seawater acidification has no effect on sinking velocity of a Mediterranean E. huxleyi strain, while nutrient limitation seems to have a small negative effect on sinking velocity. Given that warming, acidification, and lowered nutrient availability will occur simultaneously under climate change scenarios, the question is what the net effect of different influential factors will be. For example, will the effects of warming and nutrient limitation cancel? This question cannot be answered conclusively but analyses of field samples in addition to laboratory culture studies will improve predictions because in field samples multi-factor influences and even evolutionary changes are not excluded. As mentioned above, the approach of determining sinking rate followed here is applicable to field samples. Future studies could use it to analyse not only seasonal and geographic patterns but also changes in sinking velocity over geological time scales.

Small eukaryotic phytoplankton communities in tropical waters off Brazil are dominated by symbioses between Haptophyta and nitrogen-fixing cyanobacteria.

Symbioses between eukaryotic algae and nitrogen-fixing cyanobacteria have been recognized in recent years as a key source of new nitrogen in the oceans. We investigated the composition of the small photosynthetic eukaryote communities associated with nitrogen-fixing cyanobacteria in the Brazilian South Atlantic Bight using a combination of flow cytometry sorting and high throughput sequencing of two genes: the V4 region of 18S rRNA and nifH. Two distinct eukaryotic communities were often encountered, one dominated by the Mamiellophyceae Bathycoccus and Ostreococcus, and one dominated by a prymnesiophyte known to live in symbiosis with the UCYN-A1 nitrogen-fixing cyanobacterium. Among nifH sequences, those from UCYN-A1 were most abundant but three other UCYN-A clades (A2, A3, A4) were also found. Network analysis confirmed the relation between A1 and A2 clades and their hypothesized hosts and pointed out to the potential association between novel clade A4 with Braarudosphaera bigelowii, previously hypothesized to host A2.

Realized niche analysis of phytoplankton communities involving HAB: Phaeocystis spp. as a case study.

The link between harmful algal blooms, phytoplankton community dynamics and global environmental change is not well understood. To tackle this challenging question, a new method was used to reveal how phytoplankton communities responded to environmental change with the occurrence of an harmful algae, using the coastal waters of the eastern English Channel as a case study. The great interannual variability in the magnitude and intensity of Phaeocystis spp. blooms, along with diatoms, compared to the ongoing gradual decrease in anthropogenic nutrient concentration and rebalancing of nutrient ratios; suggests that other factors, such as competition for resources, may also play an important role. A realized niche approach was used with the Outlying Mean Index analysis and the dynamics of the species' realized subniches were estimated using the Within Outlying Mean Indexes calculations under low (L) and high (H) contrasting Phaeocystis spp. abundance. The Within Outlying Mean Indexes allows the decomposition of the realized niche into realized subniches, found within the subset of habitat conditions and constrained by a subset of a biotic factor. The two contrasting scenarios were characterized by significantly different subsets of environmental conditions and diatom species (BV-step analysis), and different seasonality in salinity, turbidity, and nutrients. The subset L environmental conditions were potentially favorable for Phaeocystis spp. but it suffered from competitive exclusion by key diatom species such as Skeletonema spp., Thalassiosira gravida, Thalassionema nitzschioides and the Pseudo-nitzchia seriata complex. Accordingly, these diatoms species occupied 81% of Phaeocystis spp.'s existing fundamental subniche. In contrast, the greater number of diatoms, correlated with the community trend, within subset H exerted a weaker biological constraint and favored Phaeocystis spp. realized subniche expansion. In conclusion, the results strongly suggest that both abiotic and biotic interactions should be considered to understand Phaeocystis spp. blooms with greater consideration of the preceeding diatoms. HABs needs must therefore be studied as part of the total phytoplankton community.

Community structure of photosynthetic picoeukaryotes differs in lakes with different trophic statuses along the middle-lower reaches of the Yangtze River.

Photosynthetic picoeukaryotes (PPEs) play an important role in aquatic ecosystem functioning. There is still a relative lack of information on freshwater PPEs, especially in eutrophic lakes. We used a combination of flow cytometric sorting and pyrosequencing to investigate the PPEs community structure in more than 20 mesotrophic and eutrophic lakes along the middle-lower reaches of the Yangtze River in China. The abundance of PPEs ranged between 2.04 × 103 and 5.92 × 103 cells mL-1. The contribution of PPEs to total picophytoplankton abundance was generally higher in eutrophic lakes than in mesotrophic lakes. The sequencing results indicated that the Shannon diversity of PPEs was significantly higher in mesotrophic lakes than in eutrophic lakes. At the class level, PPEs were mainly dominated by three taxonomic groups, including Cryptophyceae, Coscinodiscophyceae and Chlorophyceae, and 15 additional known phytoplankton classes, including Synurophyceae, Dinophyceae, Chrysophyceae, Trebouxiophyceae and Prymnesiophyceae, were identified. Coscinodiscophyceae dominated in the most eutrophic lakes, while Chrysophyceae, Dinophyceae and other classes of PPEs were more abundant in the mesotrophic lakes. We also observed several PPEs operational taxonomic units, and those affiliated with Cyclotella atomus, Chlamydomonas sp. and Poterioochromonas malhamensis tended to be more prevalent in the eutrophic lakes. The canonical correspondence analysis and Mantel analysis highlighted the importance of environmental parameters as key drivers of PPEs community composition.

Photosynthetic Picoeukaryotes in the Land-Fast Ice of the White Sea, Russia.

The White Sea is a unique marine environment combining features of temperate and Arctic seas. The composition and abundance of photosynthetic picoeukaryotes (PPEs) were investigated in the land-fast ice of the White Sea, Russia, in March 2013 and 2014. High-throughput tag sequencing (Illumina MiSeq system) of the V4 region of the 18S rRNA gene was used to reveal the diversity of PPE ice community. The integrated PPE abundance varied from 11 × 106 cells/m2 to 364 × 106 cells/m2; the integrated biomass ranged from 0.02 to 0.26 mg С/m2. The composition of sea-ice PPEs was represented by 16 algae genera belonging to eight classes and three super-groups. Chlorophyta, especially Mamiellophyceae, dominated among ice PPEs. The detailed analysis revealed the latent diversity of Micromonas and Mantоniella. Micromonas clade E2 revealed in the subarctic White Sea ice indicates that the area of distribution of this species is wider than previously thought. We suppose there exists a new Micromonas clade F. Micromonas clade C and Minutocellulus polymorphus were first discovered in the ice and extend the modern concept of sympagic communities' diversity generally and highlights the importance of further targeting subarctic sea ice for microbial study.

Chimeric origins of ochrophytes and haptophytes revealed through an ancient plastid proteome.

Plastids are supported by a wide range of proteins encoded within the nucleus and imported from the cytoplasm. These plastid-targeted proteins may originate from the endosymbiont, the host, or other sources entirely. Here, we identify and characterise 770 plastid-targeted proteins that are conserved across the ochrophytes, a major group of algae including diatoms, pelagophytes and kelps, that possess plastids derived from red algae. We show that the ancestral ochrophyte plastid proteome was an evolutionary chimera, with 25% of its phylogenetically tractable nucleus-encoded proteins deriving from green algae. We additionally show that functional mixing of host and plastid proteomes, such as through dual-targeting, is an ancestral feature of plastid evolution. Finally, we detect a clear phylogenetic signal from one ochrophyte subgroup, the lineage containing pelagophytes and dictyochophytes, in plastid-targeted proteins from another major algal lineage, the haptophytes. This may represent a possible serial endosymbiosis event deep in eukaryotic evolutionary history.

Change in Emiliania huxleyi Virus Assemblage Diversity but Not in Host Genetic Composition during an Ocean Acidification Mesocosm Experiment.

Effects of elevated pCO2 on Emiliania huxleyi genetic diversity and the viruses that infect E. huxleyi (EhVs) have been investigated in large volume enclosures in a Norwegian fjord. Triplicate enclosures were bubbled with air enriched with CO2 to 760 ppmv whilst the other three enclosures were bubbled with air at ambient pCO2; phytoplankton growth was initiated by the addition of nitrate and phosphate. E. huxleyi was the dominant coccolithophore in all enclosures, but no difference in genetic diversity, based on DGGE analysis using primers specific to the calcium binding protein gene (gpa) were detected in any of the treatments. Chlorophyll concentrations and primary production were lower in the three elevated pCO2 treatments than in the ambient treatments. However, although coccolithophores numbers were reduced in two of the high-pCO2 treatments; in the third, there was no suppression of coccolithophores numbers, which were very similar to the three ambient treatments. In contrast, there was considerable variation in genetic diversity in the EhVs, as determined by analysis of the major capsid protein (mcp) gene. EhV diversity was much lower in the high-pCO2 treatment enclosure that did not show inhibition of E. huxleyi growth. Since virus infection is generally implicated as a major factor in terminating phytoplankton blooms, it is suggested that no study of the effect of ocean acidification in phytoplankton can be complete if it does not include an assessment of viruses.

Haptophyte Diversity and Vertical Distribution Explored by 18S and 28S Ribosomal RNA Gene Metabarcoding and Scanning Electron Microscopy.

Haptophyta encompasses more than 300 species of mostly marine pico- and nanoplanktonic flagellates. Our aims were to investigate the Oslofjorden haptophyte diversity and vertical distribution by metabarcoding, and to improve the approach to study haptophyte community composition, richness and proportional abundance by comparing two rRNA markers and scanning electron microscopy (SEM). Samples were collected in August 2013 at the Outer Oslofjorden, Norway. Total RNA/cDNA was amplified by haptophyte-specific primers targeting the V4 region of the 18S, and the D1-D2 region of the 28S rRNA. Taxonomy was assigned using curated haptophyte reference databases and phylogenetic analyses. Both marker genes showed Chrysochromulinaceae and Prymnesiaceae to be the families with highest number of Operational Taxonomic Units (OTUs), as well as proportional abundance. The 18S rRNA data set also contained OTUs assigned to eight supported and defined clades consisting of environmental sequences only, possibly representing novel lineages from family to class. We also recorded new species for the area. Comparing coccolithophores by SEM with metabarcoding shows a good correspondence with the 18S rRNA gene proportional abundances. Our results contribute to link morphological and molecular data and 28S to 18S rRNA gene sequences of haptophytes without cultured representatives, and to improve metabarcoding methodology.

A bottom-up perspective on ecosystem change in Mesozoic oceans.

Mesozoic and Early Cenozoic marine animals across multiple phyla record secular trends in morphology, environmental distribution, and inferred behaviour that are parsimoniously explained in terms of increased selection pressure from durophagous predators. Another systemic change in Mesozoic marine ecosystems, less widely appreciated than the first, may help to explain the observed animal record. Fossils, biomarker molecules, and molecular clocks indicate a major shift in phytoplankton composition, as mixotrophic dinoflagellates, coccolithophorids and, later, diatoms radiated across shelves. Models originally developed to probe the ecology and biogeography of modern phytoplankton enable us to evaluate the ecosystem consequences of these phytoplankton radiations. In particular, our models suggest that the radiation of mixotrophic dinoflagellates and the subsequent diversification of marine diatoms would have accelerated the transfer of primary production upward into larger size classes and higher trophic levels. Thus, phytoplankton evolution provides a mechanism capable of facilitating the observed evolutionary shift in Mesozoic marine animals.

The uronic acid content of coccolith-associated polysaccharides provides insight into coccolithogenesis and past climate.

Unicellular phytoplanktonic algae (coccolithophores) are among the most prolific producers of calcium carbonate on the planet, with a production of ∼1026 coccoliths per year. During their lith formation, coccolithophores mainly employ coccolith-associated polysaccharides (CAPs) for the regulation of crystal nucleation and growth. These macromolecules interact with the intracellular calcifying compartment (coccolith vesicle) through the charged carboxyl groups of their uronic acid residues. Here we report the isolation of CAPs from modern day coccolithophores and their prehistoric predecessors and we demonstrate that their uronic acid content (UAC) offers a species-specific signature. We also show that there is a correlation between the UAC of CAPs and the internal saturation state of the coccolith vesicle that, for most geologically abundant species, is inextricably linked to carbon availability. These findings suggest that the UAC of CAPs reports on the adaptation of coccolithogenesis to environmental changes and can be used for the estimation of past CO2 concentrations.