Strontium/Calcium ratio, carbon and oxygen stable isotopes in coccolith carbonate from different grain-size fractions in South Atlantic surface sediments

In this study, the Strontium/Calcium (Sr/Ca) ratio, and the carbon and oxygen isotopic compositions of coccoliths are investigated in three different grain-size fractions (<20 μm, 15-5 μm, <5 μm) of 17 surface sediment samples from the Equatorial and South Atlantic. The results are compared to environmental parameters in order to assess the factors controlling the observed coccolith geochemical patterns. Isotopic and geochemical composition of coccolith species in surface sediment samples from the South Atlantic greatly varies according to the different grain-size fractions. However, even if the absolute values show a great offset, the general trends are comparable. The δ¹⁸O values show a decreasing trend with increasing temperature. The δ¹³C and Sr/Ca ratio are mainly influenced by productivity of coccolithophores, which is in turn controlled by different factors, such as temperature, nutrient supply and productivity of other phytoplankton groups. Dilution and dissolution are negligible factors in these open marine samples. Therefore, coccolith abundance in bulk sediment is the best approximation for productivity of coccolithophores. The various coccolith species fractionate Sr differently, as is best shown by the 5-15 μm fraction where three species (Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus) predominantly occur.     

Coccolithophores in the equatorial Atlantic Ocean: response to seasonal and Late Quaternary surface water variability

The present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial Atlantic. Data from a range of different samples, from the plankton, surface sediments as well as sediment cores are shown and compared with each other.In general, the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns. Cell densities reached a maximum of up to 300×10³ coccospheres/l in the upwelling area of the equatorial Atlantic. Here, Emiliania huxleyi is the dominant species with relatively high cell numbers, whereas Umbellosphaera irregularis and Umbellosphaera tenuis are characteristic for oligotrophic surface waters. Although they are observed in high relative abundances, these species only occur in low absolute numbers. The lower photic zone is dominated by high abundances and considerable cell numbers of Florisphaera profunda.The geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses. However, abundances of the oligotrophic species Umbellosphaera irregularis and Umbellosphaera tenuis are strongly diminished, causing an increase in relative abundance of the lower photic zone taxa Florisphaera profunda and Gladiolithus flabellatus.During the past 140,000 years the surface water circulation of the equatorial Atlantic has changed drastically, as can be seen from changes in the coccolithophore species composition, absolute coccolith numbers, as well as coccolith accumulation rates. Significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial Atlantic during the last glacial interval (oxygen isotope stages 2–4), which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site. In the western equatorial Atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods, which probably is caused by a deepening of the thermocline.     

Determination of absolute coccolith abundances in deep-sea sediments by spiking with microbeads and spraying (SMS-method)

A quick new method is described for the quantification of absolute nannofossil proportions in deep-sea sediments. This method (SMS) is the combination of Spiking a sample with Microbeads and Spraying it on a cover slide. It is suitable for scanning electron microscope (SEM) analyses and for light microscope (LM) analyses. Repeated preparation and counting of the same sample (30 times) revealed a standard deviation of ±10.5%. The application of tracer microbeads with different diameters and densities revealed no statistically significant differences between counts. The SMS-method yielded coccolith numbers that are statistically not significantly different from values obtained from the filtration-method. However, coccolith counts obtained by the random settling method are three times higher than the values obtained by the SMS- and the filtration-method.     

Ultrastructure and taxonomy ofJomonlithus littoralis gen. et sp. nov. (Class prymnesiophyceae), a coccolithophorid from the Northwest Pacific

A new coccolithophorid genusJomonlithus withJ. littoralis as the type species, is described based on specimens isolated from a sand sample collected at the mouth of Nakagawa river, Ibaraki, Japan. This genus is characterized by the coccolith which is composed of an organic base-plate scale and calcified rim elements made up of two different subelements.J. littoralis has been found in several localities along the coast of Japan. Culture and ultrastructure studies gave special attention to the cell cycle, coccolith and scale morphology and the ultrastructure of the cellular organelles. It was confirmed thatJomonlithus is similar toWigwamma Mantonet al., Papposphaera Tangen andPappomonas Manton et Oates on the basis of coccolith morphology and toCricosphaera Braarud andHymenomonas Stein in cellular structure.     

Morphologic variability of the coccolithophorid Calcidiscus leptoporus in the plankton, surface sediments and from the Early Pleistocene

On a global scale, morphological variability of the extant coccolithophorid Calcidiscus leptoporus (Murray and Blackman, 1898) Loeblich and Tappan was investigated in surface sediments and plankton samples and from an Early Pleistocene time-slice (1.8 Ma to 1.6 Ma). In the bivariate space coccolith diameter versus number of rays in the distal shield, Holocene samples follow a single, unimodal morphocline. Sample means of coccolith size and number of elements group in three clusters, I, II and III, which are of biogeographic significance. Clusters II and III coccoliths (mean coccolith size of 5.0 μm and 20.9 elements, and 6.6 μm and 25.6 elements, respectively) are found in a tropical belt extending from 11 °N to 17 °S with an annual minimum sea-surface temperature above 23.5 °C. Cluster I coccoliths (5.8 μm, 20.7 elements) are found in samples outside that belt. The distribution of coccoliths in the surface sediments is tentatively interpreted to be a result of mixing to a varying degree of at least three different morphotypes (‘small’, ‘intermediate’ and ‘large’), which were identified in the living plankton, and which are separated from each other at 5 μm and 8 μm mean coccolith diameter, respectively. A comparison of the surface sediments with the Early Pleistocene assemblages revealed that between 1.6 Ma and 1.8 Ma two morphoclines A and B existed, the first of which persisted until the Holocene in the form of C. leptoporus, while the second comprises only extinct morphotypes including Calcidiscus macintyrei as one end-member. During the Early Pleistocene morphocline A was more homogeneous and no clusters were evident.Morphocline B shows a clear bimodality with a separation of morphotypes at 9.5 μm. Our observations suggest that morphoclines are subsets within the total stratigraphical range of a single species, and represent the global variability of that species in a particular time interval. Morphotypes, which belong to a morphocline, represent the infra-specific variability of that species within the biogeographic and stratigraphic limits of that species.     

Biometry of Upper Cretaceous (Cenomanian–Maastrichtian) coccoliths – a record of long-term stability and interspecies size shifts

Biometric measurements of Mesozoic coccoliths (coccolith length and width) have been used in short-term biostratigraphic, taxonomic and palaeoecologic studies, but until now, not over longer time scales. Here, we present a long time-series study (∼ 30 million years) for the Upper Cretaceous, which aims to identify broad trends in coccolith size and to understand the factors governing coccolith size change over long time scales. We have generated biometric data for the dominant Upper Cretaceous coccolith groups, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa and Watznaueria, from 36 Cenomanian–Maastrichtian (100.5–66 Ma) samples from Goban Spur in the northeast Atlantic (DSDP Site 549). These data show that the coccolith sizes within Prediscosphaera, Retecapsa and Watznaueria were relatively stable through the Late Cretaceous, with mean size variation less than 0.7 μm. Within the Broinsonia/Arkhangelskiella group there was more pronounced variation, with a mean size increase from ∼ 6 μm in the Cenomanian to ∼ 10 μm in the Campanian. This significant change in mean size was largely driven by evolutionary turnover (species origination and extinctions), and, in particular, the appearance of larger species/subspecies (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) in the early Campanian, replacing smaller species, such as Broinsonia signata and Broinsonia enormis. Shorter-term size fluctuations within Broinsonia/Arkhangelskiella, observed across the Late Cenomanian–Turonian and Late Campanian–Maastrichtian intervals, may, however, reflect changing palaeoenvironmental conditions, such as sea surface temperature and nutrient availability.     

Coccolith Sr/Ca ratios in the eastern Mediterranean: Production versus export processes

Samples collected by two sediment traps located southwest of Crete in the eastern Mediterranean (EMED) [48A (1953 m) and 48B (950 m)] from June 2005 to May 2006 were used to study fluxes of organic carbon, carbonate and coccolithophores in combination with the variations of Sr/Ca ratios in different individually picked coccolith species. Considering the complexity of the EMED, we validate the use of Sr/Ca ratios as productivity proxy and unravel the varied processes which may influence it. We examined the relationship between the seasonal peaks in export fluxes and the Sr/Ca ratio in coccoliths of three upper photic zone coccolithophores species collected in the traps, Calcidiscus leptoporus, Helicosphaera carteri and Emiliania huxleyi. We aimed at testing whether high export fluxes are correlated with high Sr/Ca ratios, suggestive of higher nutrient-stimulated production, or Sr/Ca ratios are unchanged during high export periods, suggestive of increased export efficiency or scavenging. Periods of enhanced trap fluxes in March and June result from surface water blooms recognized in satellite imagery. An additional peak flux was found in January, but this peak represents re-suspended or recycled material in the water column.The amplitude of seasonal variations in the Sr/Ca ratios of the three investigated species is small in both traps. In the shallow trap, a decrease in the Sr/Ca ratio of C. leptoporus occurred synchronously with minimal fluxes. The other two species were not measured for this period. In the deep trap, no such decrease in Sr/Ca was observed during minimal fluxes, in either C. leptoporus or H. carteri, probably due to a long residence of coccoliths in the water column, recycling and low export efficiency. Absolute Sr/Ca ratios for all species are lower than in other more productive environments like the Bay of Bengal, Arabian Sea, or Sargasso Sea. We conclude that Sr/Ca ratios in coccoliths of surface sediments in the EMED reflect mainly spring–summer bloom conditions averaged over hundreds to thousands of years.In addition, the origin of varying calcite thickness in H. carteri was investigated. The similarity of average Sr/Ca ratios in differently-calcified specimens confirms that coccolith thickness variations in this species result from primary biomineralization processes and not from variable overgrowth by (low Sr) abiogenic calcite in the water column or the sediments.     

Stable isotope and trace element geochemistry of Upper Cretaceous carbonates and belemnite rostra (Middle Campanian, north Germany)

Trace element contents and stable isotopic composition of Middle Campanian marl-limestone rhythmites and belemnite rostra of Belemnitella mucronata were investigated. High strontium and low iron as well as manganese and magnesium contents of belemnite calcite and bulk rock samples suggest no diagenetic overprint. However, the orange-coloured cathodoluminescence of coccolith-rich sediments indicates diagenetic cementation and/or recrystallization. The non-luminescent belemnite rostra reveal an extraordinary preservation of the microstructures that is interpreted to have been favoured by a silification of the outer rim of the belemnite rostra. Carbon isotope ratios of the coccolith limestones and belemnite rostra are comparable, with higher δ¹³C variations observed for belemnite calcite. The 1.5-2‰ depletion in δ¹⁸O of the marl-limestone rhythmites relative to belemnite calcite is explained by diagenetic alteration of the sediments. Palaeotemperatures, calculated from the δ¹⁸O values of the well-preserved belemnite rostra, are around 12.5 ± 2 °C and suggest rather low sea-surface temperatures for the Middle Campanian epicontinental sea of north Germany assuming a water depth of less than 100 m.     

Paleoenvironmental controls on the morphology and abundance of the coccolith Watznaueria britannica (Late Jurassic,southern Germany)

The coccolithophore species Watznaueria britannica is dominant in Middle-Upper Jurassic calcareous nannofossil assemblages and presents morphological variation, including different coccolith size, shape and length of the central area and of the bridge. Six morphotypes can be recognized in the polarizing light microscope. The aim of this work is to better understand the morphological variability of W. britannica and determine if this variability is controlled by paleoecological factors. In order to investigate the potential paleoecological controls on W. britannica morphology and abundance, we carried out a biometric study on a restricted temporal interval: the Late Oxfordian, in the Swabian Alb (southern Germany), characterized by increasing carbonate production linked to climatic changes. The Balingen–Tieringen section, where previous works on sedimentology, nannofossil assemblage composition, and δ¹⁸O and δ¹³C analyses were performed, was selected for this study. The variations in morphology and abundances of W. britannica were studied on 40 samples of the Balingen–Tieringen section, presenting variable lithologies and calcium carbonate contents. For each level, seven biometric parameters (coccolith length, width and ellipticity, central area length, width and ellipticity and central area proportion with respect to the coccolith) were measured or calculated on digitally captured images of the first 100 W. britannica coccoliths observed in the light microscope. The relationships between the different biometric variables were described using bivariate and Principal Component Analyses. Biometric parameters and Principal Component factors extracted from nannofossil assemblages as well as other paleoenvironmental proxies, were investigated using regression, and their stratigraphic trends were compared. Principal component analysis of the six biometric variables (3938 measurements) on W. britannica coccoliths shows a reduced morphological variability compared to a significant size gradient. An allometric trend recognized on the total placolith and on the central area within the W. britannica assemblages suggests that the different morphotypes may represent intra-specific variability rather than different species. The general trend through Late Oxfordian shows an increase in size of W. britannica coccoliths, mainly driven by an increase in the contribution of the large morphotypes. Increasing placolith size is associated with drier and warmer climatic conditions during the latest Oxfordian.     

Evolution of the coccolith genus Lotharingius during the Late Pliensbachian-Early Toarcian interval in Asturias (N Spain). Consequences of the Early Toarcian environmental perturbations

The evolution of the coccolith genus Lotharingius was investigated in 18 samples from the West Rodiles section (Asturias, Northern Spain), Upper Pliensbachian-Lower Toarcian in age. In each sample, the length and width of the coccolith and of its central area were measured on 150 specimens of Lotharingius. A total of 2700 specimens were measured, and 10,800 measurements were obtained. Based on the results of the morphometric analysis, the stratigraphic ranges, the abundance patterns and the light microscope observations, the aims of this work are to determine whether the specimens analysed correspond to different species, to distinct ecophenotypes or to an anagenetic lineage of morphotypes of a single species with overlapping stratigraphic ranges, and to test the influence of the paleoenvironmental perturbations during the Early Toarcian on the studied genus. Three species of Lotharingius were distinguished: L. hauffii, L. sigillatus and L. crucicentralis. Based on central area size and structure, two morphotypes (A and B) of L. hauffii were differentiated. All the parameters measured show a great overlap between the morphotypes and species. An increase in both coccolith and central area size and a development of more complex central area structures were observed through the studied section. L. hauffii is the smallest form, followed by L. sigillatus, and finally L. crucicentralis is the largest species and has the most complex central area structure. A clear decrease in size or “dwarfing” of the species was observed in the samples corresponding to the Early Toarcian environmental perturbations. L. crucicentralis was not identified in these samples. We hypothesize that the changes in size and abundance of the Lotharingius species could be related to the unfavourable palaeoenvironmental conditions for the biomineralization of their coccoliths.     

Variability of Symbiodinium Communities in Waters,Sediments, and Corals of Thermally Distinct Reef Pools in American Samoa

Reef-building corals host assemblages of symbiotic algae (Symbiodinium spp.) whose diversity and abundance may fluctuate under different conditions, potentially facilitating acclimatization to environmental change. The composition of free-living Symbiodinium in reef waters and sediments may also be environmentally labile and may influence symbiotic assemblages by mediating supply and dispersal. The magnitude and spatial scales of environmental influence over Symbiodinium composition in different reef habitat compartments are, however, not well understood. We used pyrosequencing to compare Symbiodinium in sediments, water, and ten coral species between two backreef pools in American Samoa with contrasting thermal environments. We found distinct compartmental assemblages of clades A, C, D, F, and/or G Symbiodinium types, with strong differences between pools in water, sediments, and two coral species. In the pool with higher and more variable temperatures, abundance of various clade A and C types differed compared to the other pool, while abundance of D types was lower in sediments but higher in water and in Pavona venosa, revealing an altered habitat distribution and potential linkages among compartments. The lack of between-pool effects in other coral species was due to either low overall variability (in the case of Porites) or high within-pool variability. Symbiodinium communities in water and sediment also showed within-pool structure, indicating that environmental influences may operate over multiple, small spatial scales. This work suggests that Symbiodinium composition is highly labile in reef waters, sediments, and some corals, but the underlying drivers and functional consequences of this plasticity require further testing with high spatial resolution biological and environmental sampling.     

Long-chain alkenes and alkenones in the marine coccolithophorid Emiliania huxleyi

Very long-chain n-alkenes and n-alkenones have been identified in the ubiquitous marine alga Emiliania huxleyi. The alkenes range from C₃₁ to C₃₈ and are almost exclusively odd-chain. Dienes, trienes and tetraenes were identified but no monoenes were found. The ketones ranged from C₃₇ to C₃₉ and consisted of both alken-2-ones and alken-3-ones, with trienes more abundant than dienes. Examination of three different forms of the alga, i.e. motile, sessile and coccolith, indicated that these ketones are formed throughout the growth cycle with only minor variations in the relative proportions of the individual compounds. Although these novel compounds have not been reported previously in organisms, they are widespread in marine sediments and may be useful biological markers for E. huxleyi input to sediments.     

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.     

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.     

Coccolithogenesis In Scyphosphaera apsteinii (Prymnesiophyceae)

Coccolithophores are the most significant producers of marine biogenic calcite, although the intracellular calcification process is poorly understood. In the case of Scyphosphaera apsteinii Lohmann 1902, flat ovoid muroliths and bulky, vase‐shaped lopadoliths with a range of intermediate morphologies may be produced by a single cell. This polymorphic species is within the Zygodiscales, a group that remains understudied with respect to ultrastructure and coccolith ontogeny. We therefore undertook an analysis of cell ultrastructure, morphology, and coccolithogenesis. The cell ultrastructure showed many typical haptophyte features, with calcification following a similar pattern to that described for other heterococcolith bearing species including Emiliania huxleyi. Of particular significance was the reticular body role in governing fine‐scale morphology, specifically the central pore formation of the coccolith. Our observations also highlighted the essential role of the inter‐ and intracrystalline organic matrix in growth and arrangement of the coccolith calcite. S. apsteinii secreted mature coccoliths that attached to the plasma membrane via fibrillar material. Time‐lapse light microscopy demonstrated secretion of lopadoliths occurred base first before being actively repositioned at the cell surface. Significantly, growth irradiance influenced the coccosphere composition with fewer lopadoliths being formed relative to muroliths at higher light intensities. Overall, our observations support dynamic metabolic (i.e., in response to growth irradiance), sensory and cytoskeletal control over the morphology and secretion of polymorphic heterococcoliths. With a basic understanding of calcification established, S. apsteinii could be a valuable model to further study coccolithophore calcification and cell physiological responses to ocean acidification.     

Fossil bivalves in marine sediments of Vestfold Hills in Eastern Antarctica

Bivalves collected in Vestfold Hills during the 55th Russian Antarctic Expedition (RAE, 2009?2010) are represented by five species. Four of them (Laternula elliptica, Thracia meridionalis, Adamussium colbecki, and Philobrya sublaevis) were collected in the sediments that filled the coastal lake terraces during the Holocene; these species are still abundant on the Antarctic shelf at present. Bivalves were found in eight samples, with L. elliptica shells and fragments thereof found in seven of those samples. The sample collected near Deep Lake had the most diverse species composition, as it contained all four species named above. Shells of named species widely occurring in present-day Antarctica were found high above sea level in the marine sediments of the oasis. This indicate to the similarity of the oasis habitats in the past and the recent marine conditions. Fragments of shells of the fifth (now extinct) species Ruthipecten tuftsensis were found in glacial–marine sediments of the Marine Plain dating back to the late Pleistocene. The present study of fossil bivalves from the late Cenozoic marine sediments in Vestfold Hills is the first of its kind in Russia.     

The effect of wrack composition and diversity on macrofaunal assemblages in intertidal marine sediments

Wrack (dead, washed-up seaweed and seagrass) buried in soft substrata may increase the organic content and alter the physical structure of sediments. These effects may influence the composition and structure of macrofaunal assemblages in the sediment. Such influences can be expected to vary according to the type and amount of wrack as well as the presence of invasive seaweeds in the wrack. In this study, we deliberately buried different amounts of the invasive species Sargassum muticum in isolation or mixed to the native species Ulva sp. and Fucus vesiculosus, in two intertidal sandflats to test some hypotheses about the response of macrofaunal assemblages. We tested whether (1) diversity of detritus (i.e. different mixtures), and (2) the amount of detritus of S. muticum influenced the composition and the relative abundance of macrofaunal assemblages. We also assessed whether the sediment organic carbon and the biomass of benthic microalgae varied depending on the diversity of detritus and the amount of detritus of S. muticum. Finally, we tested if these effects of wrack were consistent across sites. Results indicated that buried wrack affected the composition and structure of macrofaunal assemblages in short-term (i.e. 4 weeks), but there were no differences depending on detritus diversity or the amount of S. muticum. In addition, sediment organic matter and microalgal biomass were not affected by the addition of wrack. They instead varied greatly among small spatial scales (i.e. plots). Wrack composition or abundance of the invasive species S. muticum played thus a small role in shaping the structure of macrofaunal assemblages or the biomass of benthic microalgae in these intertidal sediments, probably because these sediments are frequently affected by various inputs of organic matter and benthic assemblages are already adapted to organically enriched sediments.     

Sequential Coccolith Morphogenesis in Hymenomonas carterae

SYNOPSIS. A careful re-examination with refined technics of the ultrastructure of the formation of calcified scales (coccoliths) in the marine unicellular alga Hymenomonas carterae has yielded new and more detailed information about the structure and morphogenesis of these unique and complex Golgi-elaborated organelles. The coccolith rim is formed from 2 distinct, alternating, anvil-shaped elements, 13–16 each, fitted together with a “right-handed” asymmetry. The coccolith is assembled in Golgi cisternae from 2 precursors, a single, scale-like base and multiple granular elements called coccolithosomes. The association of scales and coccolithosomes and subsequent development to the mature coccolith occur in a characteristic sequential fashion within what is one of the better examples of a polarized Golgi. Morphogenesis involves a special cisternal membrane association with the base of the coccolith, the contribution of granular material by coccolithosomes to form the outer rim matrix, and the subsequent filling of the area enclosed by the matrix with an electron-dense material, presumably CaCO₃. A “microenvironment” model system for species specific shape-determination of calcified elements is proposed.     

Diversity and composition of bacterial community in the rhizosphere sediments of submerged macrophytes revealed by 454 pyrosequencing

Freshwater lake sediments support a variety of submerged macrophytes that may host groups of bacteria exerting important ecological functions. We collected three kinds of commonly found submerged macrophyte species (Ceratophyllum demersum, Vallisneria spiralis and Elodea nuttallii) to investigate the bacterial community associated with their rhizosphere sediments. High-throughput 454 pyrosequencing and bioinformatics analyses were performed to examine the diversity and composition of the bacterial community. The results obtained indicated that the diversity of the bacterial community associated with the rhizosphere sediments of submerged macrophytes was significantly lower than that of the bulk sediment. Remarkable differences in the bacterial community composition between the rhizosphere and bulk sediments were also observed.     

Seasonal occurrence of coccoliths in sediment traps from West Caroline Basin, equatorial West Pacific Ocean

Coccolith fluxes were investigated by sediment trap studies in the West Caroline Basin, which is located in the equatorial western Pacific. The investigation was conducted from June 1991 to March 1992 at two water depths, 1592 and 3902 m, as part of the Northwest Pacific Carbon Cycle Study (NOPACCS) program. Two seasonal maxima of coccolith fluxes were observed during September–early October and late December–January. The average coccolith and coccosphere fluxes at the depth of the shallow trap were 1800×10⁶ coccoliths m⁻² day⁻¹ and 1.9×10⁶ coccospheres m⁻² day⁻¹, respectively. The flux of coccoliths followed the same trend as the total flux, and was closely correlated with the flux of organic matter flux. Florisphaera profunda, Gladiolithus flabellatus, Gephyrocapsa oceanica, Umbilicosphaera sibogae var. sibogae, Emiliania huxleyi, and Oolithotus fragilis were the most abundant species together comprising more than 85% of the total flora. Observed seasonal changes of the species composition of coccolith flora, as well as analysis of the R-mode cluster, revealed that during the summer, the assemblage was marked by the dominance of G. oceanica and U. sibogae. However, during the winter, the assemblage was dominated by E. huxleyi and O. fragilis. These assemblage changes were influenced by monsoonal events, which were observed off the New Guinea coast. F. profunda dominated the community in the shallow trap throughout most of the year; peak values of this species were recorded during the winter. The coccosphere assemblage was dominated by G. oceanica at both water depths. In the deep trap, the sedimentation pattern was similar to that observed at the shallow depth. Mean coccolith and coccosphere fluxes at the deep trap were 2000×10⁶ coccolith m⁻² day⁻¹ and 0.08×10⁶ coccospheres m⁻² day⁻¹, respectively. The increase in coccolith flux with water depth suggests a lateral influx. The estimated average daily mass of CaCO₃ flux in coccoliths and coccospheres was 16.6 mg m⁻² day⁻¹ at the 1592 m trap and 17.9 mg m⁻² day⁻¹ at the 3902 m trap, respectively. These calculated values contributed only 23.3% to the total CaCO₃ flux at the shallow trap and 27.9% at the deep trap.