Coccolith Morphology Research Articles

Coccoliths as Recorders of Paleoceanography and Paleoclimate over the Past 66 Million Years

Coccolithophores are a major group of oceanic calcifying phytoplankton, and their calcite skeletal remains, termed calcareous nannofossils, are a major component of deep-sea sediments accumulating since the Jurassic. Coccolithophores play a role in both the biological pump and the carbonate pump, exporting organic and inorganic carbon, respectively, out of the surface ocean. This means that they are key responders to and recorders of ocean carbon cycle and climate changes over geological and shorter timescales, and studying these responses can help elucidate the uncertain fate of calcifying phytoplankton under projected climate change scenarios. Here, we review established and emerging approaches for reconstructing (a) mixed-layer ocean temperature, (b) marine productivity, and (c) aspects of the ocean carbon cycle, using calcareous nannofossils from deep-sea sediments. For each parameter, we discuss the different proxies that have been proposed, based on abundance or species composition, inorganic geochemistry, and/or coccolith morphology, and explore their applications and limitations in Cenozoic paleoceanography. ▪ Calcareous nannofossils can be used to reconstruct upper ocean conditions and changes over centennial to million-year timescales. ▪ Key coccolith-based proxies for temperature, productivity, and the carbon cycle are reviewed. ▪ Approaches based on assemblages, geochemistry, and morphology provide novel insights into the evolution and adaptation of coccolithophores and past climate.

Stable carbon isotope ratios of pristine carbohydrates preserved within nannofossil calcite

The geochemical characterization of phytoplankton-derived organic compounds found in marine sediments has been widely used to reconstruct atmospheric pCO2 throughout the Cenozoic. This is possible owing to a well-established relationship between the carbon isotope ratios of phytoplankton biomass and CO2 concentration in the ambient seawater. An ideal molecular target for such proxy reconstructions would be degradation resistant on geologic timescales and unambiguously associated with known, experimentally tractable, organisms, so that species-specific models can be developed, calibrated, and applied to appropriate material. However, existing organic matter targets do not meet these criteria, primarily owing to ambiguity in the source species of recalcitrant compounds in deep time. Here we explore the potential of a novel organic carbon target for isotopic analysis: acidic polysaccharides extracted from the calcite plates (coccoliths) that are produced by all calcifying haptophytes. Carbohydrates are usually rapidly remineralized in sediments, but coccolith-associated polysaccharides (CAPs) are mechanically protected from diagenesis within the coccolith calcite lattice. Coccoliths can be taxonomically separated by size and identified, often to species level, prior to CAP extraction, providing a species-specific record. Coccolith morphology and composition are important additional sources of information, which are then unambiguously associated with the extracted CAPs. We found that carbon isotope ratios of CAPs changed in response to the environmental changes associated with a glacial cycle, which we attribute to temperature-driven changes in average growth rate. Once the underlying biosynthetic processes and the associated isotope effects are better understood, this archive of pristine organic matter has the potential to provide insight into phytoplankton growth rates and atmospheric pCO2 far beyond the Cenozoic, to when the first coccolithophores inhabited the surface ocean over 200 million years ago.

Evolutionary change of crystallographic orientation and coccolith morphology: Neogene-Quaternary Umbilicosphaera (Prymnesiophyceae) lineage

The crystallographic orientation and its relationship to the morphology of coccoliths were investigated for the Neogene-Quaternary calcareous nannoplankton Umbilicosphaera lineage using scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). The c-axis of the calcite forming the distal shield elements was inclined upward at 66–68° (U. sibogae), 65–68° (U. foliosa), 57–58° (U. rotula), and 55–57° (U. patera) from the coccolith plane. Accordingly, the outward dip angle of one of the {101¯4} faces forming the surface of the distal shield of U. patera coccolith was shallower than those of U. sibogae and U. foliosa, explaining the nearly flat distal shield and the steep inner slope, formed by another equivalent {101¯4} face, around the central opening of U. patera. Our results showed that the evolution from U. rotula to U. patera during the Late Miocene was not accompanied by a change in crystallographic orientation. In contrast, the evolution from U. patera to U. sibogae and U. foliosa during the Pliocene was accompanied by a rotation of the orientation. The crystallographic orientation of calcite nuclei on the baseplate with a combination of other factors would have resulted in species-specific differences in shield shape and suture lines within the same phylogeny, consequently producing morphological diversity in the coccolith throughout geological time.

Evolutionary change in crystallographic orientation and morphology of Cenozoic coccoliths: Insights from Toweius, Reticulofenestra, and Umbilicosphaera.

Evolutionary change in crystallographic orientation and morphology of Cenozoic coccoliths: Insights from Toweius, Reticulofenestra, and Umbilicosphaera.

Inferred nutrient forcing on the late middle Eocene to early Oligocene (~40–31 Ma) evolution of the coccolithophore Reticulofenestra (order Isochrysidales)

AbstractThe first size reduction (FSR) in the Reticulofenestra-Gephyrocapsa-Emiliania (RGE) lineage (order Isochrysidales), which occurred in the early Oligocene (~32 Ma), is of great significance for understanding the Lilliput effect that has affected coccolithophore communities from the late Eocene to this day. We conducted a morphologic analysis on the coccoliths of Reticulofenestra species that lived during the late middle Eocene to early Oligocene (~40–31 Ma), using marine sediments from the South Atlantic Ocean. Our data show increasing size and decreasing abundance of the large species during the late Eocene, leading to their disappearance at the FSR, and a concurrent decrease in the size variability of the small- to medium-sized coccoliths whose central opening diameter had become very reduced. Although the cosmopolitan late Paleogene through Neogene size decrease in coccolithophores has been linked to the concomitant long-term decline in global pCO2, we suggest here that the FSR was the result of environmental destabilization caused by the expansion of eutrophic environments following the late Eocene establishment of overturning circulation associated with ice buildup on Antarctica. This study also leads us to propose a hypothetical model that links coccolith morphology of species of the RGE lineage and trophic resources in the upper ocean: the small- to medium-sized, r-selected coccolithophores with smaller coccolith central openings live in nutrient-rich waters where they rely mostly on photosynthesis and little on mixotrophy, whereas the larger, K-selected species with larger coccolith central openings live in oligotrophic waters where they are more dependent on mixotrophy.

Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry

Abstract. Understanding the variations in past ocean carbonate chemistry is critical to elucidating the role of the oceans in balancing the global carbon cycle. The fossil shells from marine calcifiers present in the sedimentary record are widely applied as past ocean carbon cycle proxies. However, the interpretation of these records can be challenging due to the complex physiological and ecological response to the carbonate system during an organisms' life cycle and the potential for preservation at the seafloor. Here we present a new dissolution proxy based on the morphological attributes of coccolithophores from the Noëlaerhabdaceae family (Emiliania huxleyi > 2 µm, and small Gephyrocapsa spp.). To evaluate the influences of coccolithophore calcification and coccolith preservation on fossil morphology, we measured morphological attributes, mass, length, thickness, and shape factor (ks) of coccoliths in a laboratory dissolution experiment and surface sediment samples from the South China Sea. The coccolith morphological data in surface sediments were also analyzed with environment settings, namely surface temperature, nutrients, pH, chlorophyll a concentration, and carbonate saturation of bottom water by a redundancy analysis. Statistical analysis indicates that carbonate saturation of the deep ocean explains the highest proportion of variation in the morphological data instead of the environmental variables of the surface ocean. Moreover, the dissolution trajectory in the ks vs. length of coccoliths is comparable between natural samples and laboratory dissolution experiments, emphasizing the importance of carbonate saturation on fossil coccolith morphology. However, the mean ks alone cannot fully explain the main variations observed in our work. We propose that the normalized ks variation (σ/ks), which is the ratio between the standard deviation of ks (σ) and the mean ks, could reflect different degrees of dissolution and size-selective dissolution, influenced by the assemblage composition. Applied together with the σ/ks ratio, the ks factor of fossil coccoliths in deep ocean sediments could be a potential proxy for a quantitative reconstruction of past carbonate dissolution dynamics.

The Effect of cytoskeleton inhibitors on coccolith morphology in Coccolithus braarudii and Scyphosphaera apsteinii.

The calcite platelets of coccolithophores (Haptophyta), the coccoliths, are among the most elaborate biomineral structures. How these unicellular algae accomplish the complex morphogenesis of coccoliths is still largely unknown. It has long been proposed that the cytoskeleton plays a central role in shaping the growing coccoliths. Previous studies have indicated that disruption of the microtubule network led to defects in coccolith morphogenesis in Emiliania huxleyi and Coccolithus braarudii. Disruption of the actin network also led to defects in coccolith morphology in E. huxleyi, but its impact on coccolith morphology in C. braarudii was unclear, as coccolith secretion was largely inhibited under the conditions used. A more detailed examination of the role of actin and microtubule networks is therefore required to address the wider role of the cytoskeleton in coccolith morphogenesis. In this study, we have examined coccolith morphology in C. braarudii and Scyphosphaera apsteinii following treatment with the microtubule inhibitors vinblastine and colchicine (S. apsteinii only) and the actin inhibitor cytochalasin B. We found that all cytoskeleton inhibitors induced coccolith malformations, strongly suggesting that both microtubules and actin filaments are instrumental in morphogenesis. By demonstrating the requirement for the microtubule and actin networks in coccolith morphogenesis in diverse species, our results suggest that both of these cytoskeletal elements are likely to play conserved roles in defining coccolith morphology.

Cyclic evolution of phytoplankton forced by changes in tropical seasonality.

Although the role of Earth's orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment1,2. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events3. Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth's orbital eccentricity with rhythms of around 100,000 years and 405,000 years-a distinct spectral signature to that of coeval global climate cycles4. Simulations with an Earth System Model5 coupled with an ocean biogeochemical model6 show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.

Sr in coccoliths of Scyphosphaera apsteinii: Partitioning behavior and role in coccolith morphogenesis

Coccolithophores are important contributors to global calcium carbonate through their species-specific production of calcite coccoliths. Nannofossil coccolith calcite remains an important tool for paleoreconstructions through geochemical analysis of isotopic and trace element incorporation including Sr, which is a potential indicator of past surface ocean temperature and productivity. Scyphosphaera apsteinii (Zygodiscales) exhibits an unusually high Sr/Ca ratio and correspondingly high partitioning coefficient (DSr = 2.5) in their two morphologically distinct types of coccoliths: flat muroliths and barrel-like lopadoliths. Whether or not this reflects mechanistic differences in calcification compared to other coccolithophores is unknown. We therefore examined the possible role of Sr in S. apsteinii calcification by growing cells in deplete (0.33 mmol/mol Sr/Ca), ambient (9 mmol/mol Sr/Ca), and higher than ambient Sr conditions (36 and 72 mmol/mol Sr/Ca). The effects on growth, quantum efficiency of photosystem II (Fv/Fm), coccolith morphology, and calcite DSr were evaluated. No effect on S. apsteinii growth rate or Fv/Fm was observed when cells were grown in Sr/Ca between 0.33–36 mmol/mol. However, at 72 mmol/mol Sr/Ca growth rate was significantly reduced, although Fv/Fm was unaffected. Reducing the Sr/Ca from ambient (9 mmol/mol) did not significantly alter the frequency of malformed and aberrant muroliths and lopadoliths, but at higher than ambient Sr/Ca conditions coccolith morphology was significantly disrupted. This implies that Sr is not a critical determining factor in normal coccolith calcite morphology in this dimorphic species. Using energy dispersive spectroscopy (EDS) we observed an increase in [Sr] and decrease in DSr of coccoliths as the Sr/Ca of the growth medium increased. Interestingly, muroliths had significantly lower Sr/Ca than lopadoliths at ambient and elevated [Sr], and lopadolith tips had lower Sr than bases in ambient conditions. In summary, the Sr fractionation behavior of S. apsteinii is distinct from other coccolithophores because of an unusually high DSr and inter- and intra-coccolith variability in Sr/Ca. These observations could be explained by mechanistic differences in the selectivity of the Ca2+ transport pathway or in the Sr-and Ca-binding capacity of organic components, such as polysaccharides associated with coccolithogenesis.

Can morphological features of coccolithophores serve as a reliable proxy to reconstruct environmental conditions of the past?

Abstract. Morphological changes in coccoliths, tiny calcite platelets covering the outer surface of coccolithophores, can be induced by physiological responses to environmental changes. Coccoliths recovered from sedimentary successions may therefore provide information on paleo-environmental conditions prevailing at the time when the coccolithophores were alive. To calibrate the biomineralization responses of ancient coccolithophore to environmental changes, studies often compared the biological responses of living coccolithophore species with paleo-data from calcareous nannofossils. However, there is uncertainty whether the morphological responses of living coccolithophores are representative of those of the fossilized ancestors. To investigate this, we exposed four living coccolithophore species (Emiliania huxleyi, Gephyrocapsa oceanica, Coccolithus pelagicus subsp. braarudii, and Pleurochrysis carterae) that have been evolutionarily distinct for hundreds of thousands to millions of years, to a range of environmental conditions (i.e., changing light intensity, Mg∕Ca ratio, nutrient availability, temperature, and carbonate chemistry) and evaluated their responses in coccolith morphology (i.e., size, length, width, malformation). The motivation for this study was to test if there is a consistent morphological response of the four species to changes in any of the tested abiotic environmental factors. If this was the case, then this could suggest that coccolith morphology can serve as a paleo-proxy for that specific factor because this response is conserved across species that have been evolutionary distinct over geological timescales. However, we found that the four species responded differently to changing light intensity, Mg∕Ca ratio, nutrient availability, and temperature in terms of coccolith morphology. The lack of a common response reveals the difficulties in using coccolith morphology as a paleo-proxy for these environmental drivers. However, a common response was observed under changing seawater carbonate chemistry (i.e., rising CO2), which consistently induced malformations. This commonality provides some confidence that malformations found in the sedimentary record could be indicative of adverse carbonate chemistry conditions.

Coccolithophore Calcification: Changing Paradigms in Changing Oceans

Coccolithophores represent a major component of the marine phytoplankton and contribute to the bulk of biogenic calcite formation on Earth. These unicellular protists produce minute calcite scales (coccoliths) within the cell, which are secreted to the cell surface. Individual coccoliths and their arrangements on the cell surface display a wide range of morphological variations. This review explores some of the recent evidence that point to similarities and differences in the mechanisms of calcification, focussing on the transport mechanisms that bring substrates to, remove product from the site of calcification, together with new findings on factors that regulate coccolith morphology. We argue that better knowledge of these mechanisms and their variations may inform more generally how different species of coccolithophore are likely to respond to changes in ocean chemistry.

Over-calcified forms of the coccolithophore <i>Emiliania huxleyi</i> in high-CO<sub>2</sub> waters are not preadapted to ocean acidification

Abstract. Marine multicellular organisms inhabiting waters with natural high fluctuations in pH appear more tolerant to acidification than conspecifics occurring in nearby stable waters, suggesting that environments of fluctuating pH hold genetic reservoirs for adaptation of key groups to ocean acidification (OA). The abundant and cosmopolitan calcifying phytoplankton Emiliania huxleyi exhibits a range of morphotypes with varying degrees of coccolith mineralization. We show that E. huxleyi populations in the naturally acidified upwelling waters of the eastern South Pacific, where pH drops below 7.8 as is predicted for the global surface ocean by the year 2100, are dominated by exceptionally over-calcified morphotypes whose distal coccolith shield can be almost solid calcite. Shifts in morphotype composition of E. huxleyi populations correlate with changes in carbonate system parameters. We tested if these correlations indicate that the hyper-calcified morphotype is adapted to OA. In experimental exposures to present-day vs. future pCO2 (400 vs. 1200 µatm), the over-calcified morphotypes showed the same growth inhibition (−29.1±6.3 %) as moderately calcified morphotypes isolated from non-acidified water (−30.7±8.8 %). Under the high-CO2–low-pH condition, production rates of particulate organic carbon (POC) increased, while production rates of particulate inorganic carbon (PIC) were maintained or decreased slightly (but not significantly), leading to lowered PIC ∕ POC ratios in all strains. There were no consistent correlations of response intensity with strain origin. The high-CO2–low-pH condition affected coccolith morphology equally or more strongly in over-calcified strains compared to moderately calcified strains. High-CO2–low-pH conditions appear not to directly select for exceptionally over-calcified morphotypes over other morphotypes, but perhaps indirectly by ecologically correlated factors. More generally, these results suggest that oceanic planktonic microorganisms, despite their rapid turnover and large population sizes, do not necessarily exhibit adaptations to naturally high-CO2 upwellings, and this ubiquitous coccolithophore may be near the limit of its capacity to adapt to ongoing ocean acidification.

Ocean warming modulates the effects of acidification on Emiliania huxleyi calcification and sinking

AbstractOngoing ocean warming and acidification are tied to the rapid accumulation of human‐induced carbon dioxide (CO2) in the atmosphere and subsequent uptake of heat and CO2 by the surface ocean. These processes are expected to drive large changes in marine ecosystems. While numerous studies have examined the effects of ocean acidification on coccolithophores, less is known on their combined effect. In this study, we investigate temperature modulation of the carbonate chemistry sensitivity of the coccolithophore Emiliania huxleyi (RCC1827 from the Western Mediterranean) in a culture experiment. We analyzed the responses of coccolith morphology, particulate inorganic and organic carbon production, and sinking rate of individual cells. E. huxleyi was exposed to three CO2 levels (ca. 400 μatm, 900 μatm, and 1400 μatm) at 15°C and 20°C. Temperature adds to the negative effect of increasing pCO2 on coccolith morphology, suggesting that a significant number of E. huxleyi strains might suffer from a temperature increase, hampering their evolutionary success. Temperature amplified the positive effect of increasing pCO2 on organic carbon production, while modulating the response of calcification rates, indicating that the response to increasing pCO2 must be taken with caution depending on the temperature range studied. Sinking rates were positively correlated with temperature, whereas pCO2 did not have any effect. The combined effect of carbonate chemistry and temperature on the E. huxleyi ratio between particulate inorganic carbon and particulate organic carbon (PIC/POC) might also lower the sinking rate of aggregates. In conclusion, in a warmer and more acidified ocean, individual coccolithophore cells might sink faster, while aggregates might sink slower.

Morphometry, biogeography and ecology of Calcidiscus and Umbilicosphaera in the South Atlantic

Here we present morphometrical evaluation, biogeographical distribution patterns and ecological information for five coccolithophore taxa (Calcidiscus leptoporus, C. leptoporus small, C. quadriperforatus, Umbilicosphaera foliosa and U. sibogae). This information is based on data obtained from surface sediments from the South Atlantic. The three Calcidiscus taxa can easily been distinguished by a combination of size and qualitative characters of their distal shields. Mostly encountered in the temperate to sub-polar regions C. leptoporus is the most abundant taxon and exhibits a negative correlation to temperature and salinity. Both, C. leptoporus small and C. quadriperforatus reach their maximum abundances also at higher latitudes and in the SW-African upwelling area. Their distributions therefore suggest preference for nutrient-enriched waters, which is also indicated by CCA. The two circular Umbilicosphaera species exhibit significant differences in coccolith morphology and show little overlap in size. Highest abundances are encountered in sub-tropical latitudes and are mainly derived from U. sibogae. In contrast, U. foliosa is present in very low abundances. Both species exhibit a preference for warm and oligotrophic conditions. However, U. foliosa increases in relative proportion to U. sibogae at the southernmost locations and in the Benguela upwelling. This could be interpreted as an affinity for slightly cooler and nutrient-enriched environments.

Coccolithophore community response to increasing pCO2 in Mediterranean oligotrophic waters

The effects of elevated partial pressure of CO2 (pCO2) on plankton communities in oligotrophic ecosystems were studied during two mesocosm experiments: one during summer 2012 in the Bay of Calvi, France, and another during winter 2013 in the Bay of Villefranche, France. Here we report on the relative abundances of coccolithophores versus siliceous phytoplankton, coccolithophore community structure, Emiliania huxleyi coccolith morphology and calcification degree. A pCO2 mediated succession of phytoplankton groups did not occur. During both experiments, coccolithophore abundance and community structure varied with time independently of pCO2 levels. Changes in the community structure were partly explained by the concentration of phosphate during the winter experiment. During the summer experiment, it was not clearly related to any of the parameters measured but possibly to changes in temperature. Phenological changes in the community and an attenuated response due to the low biomass building during the winter experiment could have masked the response to pCO2. E. huxleyi dominated the coccolithophore community in winter; it was not affected by elevated pCO2 at any time. In contrast, the abundance of Rabdosphaera clavigera, the dominant species in summer, increased with time and this increase was affected at elevated pCO2. Thus, a different coccolithophore community response based on species-specific sensitivities to pCO2 is still likely. Finally, elevated pCO2 had no traceable effect on E. huxleyi (type A) coccolith morphology or on the degree of coccolith calcification. Our results highlight the possibility that, in oligotrophic regions, nutrient availability, temperature or intrinsic phenological changes might exert larger constrains on the coccolithophore community structure than high pCO2 does solely.

Negative effects of ocean acidification on calcification vary within the coccolithophore genus Calcidiscus

A large percentage of CO2 emitted into the atmosphere is absorbed by the oceans, causing chemical changes in surface waters known as ocean acidification (OA). Despite the high interest and increased pace of OA research to understand the effects of OA on marine organisms, many ecologically important organisms remain unstudied. Calcidiscus is a heavily calcified coccolithophore genus that is widespread and genetically and morphologically diverse. It contributes substantially to global calcium carbonate production, organic carbon production, oceanic carbon burial, and ocean–atmosphere CO2 exchange. Despite the importance of this genus, relatively little work has examined its responses to OA. We examined changes in growth, morphology, and carbon allocation in multiple strains of Calcidiscus leptoporus in response to ocean acidification. We also, for the first time, examined the OA response of Calcidiscus quadriperforatus, a larger and more heavily calcified Calcidiscus congener. All Calcidiscus coccolithophores responded negatively to OA with impaired coccolith morphology and a decreased ratio of particulate inorganic to organic carbon (PIC:POC). However, strains responded variably; C. quadriperforatus showed the most sensitivity, while the most lightly calcified strain of C. leptoporus showed little response to OA. Our findings suggest that calcium carbonate production relative to organic carbon production by Calcidiscus coccolithophores may decrease in future oceans and that Calcidiscus distributions may shift if more resilient strains and species become dominant in assemblages. This study demonstrates that variable responses to OA may be strain or species specific in a way that is closely linked to physiological traits, such as cellular calcite quota.

Coccolithophorids in Polar Waters: Pappomonas spp. Revisited

A contingent of weakly calcified coccolithophorid genera and species were described from polar regions almost 40 years ago. In the interim period a few additional findings have been reported enlarging the realm of some of the species. The genus Pappomonas is revisited here with the purpose of providing, based on additional sampling from both polar regions, an update on species morphology, life history aspects and biogeography that can serve as a reference for the future. The examination of a substantial number of cells unequivocally supports the elevation to species level of P. borealis stat. nov. (previously referred to as P. flabellifera var. borealis) as a separate taxon which is different from P. flabellifera in a number of critical morphological features. Additional evidence in favour of linking P. virgulosa and Bala­niger balticus in a shared life history in combination with significant differences in coccolith morphology between the Pappomonas type species (P. flabellifera) and P. virgulosa has prompted us to synonymise Balaniger balticus with Pappomonas virgulosa , while informally keeping the names of the phases as Balaniger virgulosa HET (= Pappomonas virgulosa phase) and Balaniger virgulosa HOL (= Balaniger balticus phase ). A new species, Pappomonas garrisonii sp. nov. is described to accommodate Antarctic material from the Weddell Sea. While fitting into the Pappomonas generic concept, the species adds new dimensions to the overall appearance of the coccolith armour of the cell and emphasizes the close relationship between species of Pappomonas and Papposphaera .

Coccolithophorids in Polar Waters: Wigwamma spp. Revisited

A contingent of weakly calcified coccolithophorid genera and species were described from polar regions almost 40 years ago. In the interim period a few additional findings have been reported enlarging the realm of some of the species. The genus Wigwamma is revisited here with the purpose of providing, based on additional sampling from both polar regions, an update on species morphology, life history events and biogeography that can serve as a reference for the future. A new genus, Pseudowigwamma gen. nov. is described to accommodate Wigwamma scenozonion , a species which critically deviates from a core group of five Wigwamma species in terms of coccolith morphology and life history events. Wigwamma armatura sp. nov. is described on the basis of material from the Weddell Sea, Antarctica. While fitting nicely into the Wigwamma generic concept, the species adds new dimensions to the overall appearance of the coccolith armour of the cell.

The Life Cycle and Taxonomic Affinity of the CoccolithophoreJomonlithus littoralis(Prymnesiophyceae)

Jomonlithus littoralis is a coccolithophore exhibiting unusual coccolith morphology that has previously only been reported from Japanese coastal waters. Jomonlithus is a mono-specific genus that has remained incertae sedis within the Prymnesiophyceae since its original description. We isolated a culture of the calcifying (diploid) stage of this species from Mediterranean coastal waters that subsequently produced a non-calcifying life cycle stage in culture. The non-calcifying (haploid) stage of J. littoralis is described for the first time through light and electron microscope observations of cytology, scale ornamentation and ultrastructure. A 28s rDNA molecular phylogeny is presented and the systematic affinities of Jomonlithus are discussed. This genus is placed in the Hymenomonadaceae and the diagnosis of this family is emended.

Morphology of <i>Emiliania huxleyi</i> coccoliths on the northwestern European shelf – is there an influence of carbonate chemistry?

Abstract. Within the context of the UK Ocean Acidification project, Emiliania huxleyi (type A) coccolith morphology was examined from samples collected during cruise D366. In particular, a morphometric study of coccolith size and degree of calcification was made on scanning electron microscope images of samples from shipboard CO2 perturbation experiments and from a set of environmental samples with significant variation in calcite saturation state (Ωcalcite). One bioassay in particular (E4 from the southern North Sea) yielded unambiguous results – in this bioassay exponential growth from a low initial cell density occurred with no nutrient enrichment and coccosphere numbers increased tenfold during the experiment. The samples with elevated CO2 saw significantly reduced coccolithophore growth. However, coccolithophore morphology was not significantly affected by the changing CO2 conditions even under the highest levels of perturbation (1000 μatm CO2). Environmental samples similarly showed no correlation of coccolithophore morphology with calcite saturation state. Some variation in coccolith size and degree of calcification does occur but this seems to be predominantly due to genotypic differentiation between populations on the shelf and in the open ocean.