Export production of coccolithophores in an upwelling region: Results from San Pedro Basin, Southern California Borderlands

A seven month-long time series sediment trap project was carried out in San Pedro Basin (Southern California Borderlands) in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes. This region is periodically influenced by upwelling, particularly during the spring and early summer. The highest fluxes of both whole coccospheres and individual coccoliths occurred during winter (January-February), a period when the fluxes of diatoms and planktic foraminifera were low. The highest coccolithophore fluxes were recorded in the mid-February with 860 × 10⁶ coccoliths m⁻² day⁻¹, 8 × 10⁶ whole coccospheres m⁻² day⁻¹, and 80 mg of coccolith carbonate m⁻² day⁻¹. Coccolith carbonate fluxes in January and February account for most of the total carbonate fluxes measured during this period. The season of maximum coccolithophore production in this region (winter) is correlated with weak stratification of the upper water column, low total primary production, low nutrient contents, and low temperatures.Emiliania huxleyi and Florisphaera profunda are the two most abundant species in this region. While E. huxleyi displays no distinct seasonal changes in flux, F. profunda shows a clear preference for cold, low nutrient water conditions and low light levels. Helicosphaera spp. flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity.     

A paradox of warming in a deep peri-Alpine lake (Lake Lugano,Switzerland and Italy)

Coccolithophore were collected and analyzed at 10 stations during summer 2010, from coastal and offshore areas off the eastern Libyan coast (southern Mediterranean Sea). The results were compared with oceanographic data. Total coccosphere concentrations, associated with nutrient-depleted stratified waters, show good correlation with the summer data from the central and eastern Mediterranean sites. K-strategist taxa dominate the surface/intermediate water, while Florisphaera profunda is more abundant in the deep photic zone. The canonical correlation analysis reveals that the distribution of coccolithophore taxa is influenced by environmental parameters: K-strategist taxa are related to nutrient-depleted surface/intermediate waters, whereas lower photic zone taxa are influenced by the development of a deep chlorophyll maximum and high salinity values, well below the thermocline. Finally, the occurrence of three clusters above 50 m, between 50 and 100 m, and below 100 m depth can be detected. These results confirm that a vertical species zonation, as a typical feature of low-middle latitude, characterizes the eastern Libyan coast, where the holococcolithophores represent one of the most important features of coccolithophore production during summer. The distribution of F. profunda matches the depth of the DCM layer, once again confirming its use as a proxy of DCM development and paleoproductivity estimates.     

Vertical and lateral variations in coccolithophore community structure across the subtropical frontal zone in the South Atlantic Ocean

In this study the coccolithophore compositions of 11 plankton depth stations along a N–S transect from the South Atlantic Subtropical Gyre to the Subantarctic Zone were examined qualitatively and quantitatively. The lateral and vertical distribution patterns of not only the most abundant taxa but also of the morphotypes of distinct species complexes, such as Calcidiscus leptoporus, Emiliania huxleyi, and Umbellosphaera tenuis were the focus. Geographic variation among morphotypes mirrors different ecological affinities of the members of a species complex. Multivariate statistics were used to infer the relationship between a set of known environmental data and species concentrations. The results of the detrended Canonical Correspondence Analysis (CCA) revealed the presence of distinct species assemblages. The Subtropical Gyre assemblage within the upper 50 m of the photic zone is mainly composed of Umbellosphaera irregularis, U. tenuis types III and IV, Discosphaera tubifera, Rhabdosphaera clavigera, S. pulchra and E. huxleyi var. corona, adapted to warm and oligotrophic conditions. In the deeper photic zone abundant Florisphaera profunda, Gephyrocapsa ericsonii and Oolithotus spp. are encountered, benefiting from higher nutrient concentrations in the vicinity of the nutricline. A well-defined Subtropical Frontal Zone (STFZ) association is clearly dominated by E. huxleyi types A and C throughout the upper 100 m of the water column. Secondary contributors in the upper photic zone are Syracosphaera spp. (mainly S. histrica, S. molischii), Michaelsarsia elegans, Ophiaster spp. and U. tenuis type II. This assemblage is associated with cooler, nutrient-rich waters. E. huxleyi type B is found deeper in the water column. Here it is accompanied by Algirosphaera robusta, G. muellerae, and S. anthos indicating a tolerance of lower light availability in environments with elevated productivity. C. leptoporus spp. leptoporus shows relatively high cell numbers in all sampled water levels throughout the STFZ. Interestingly, its coccoliths are often smaller 5 μm in lith diameter. The mean coccolithophore assemblages of a station were compared to the underlying surface sediment assemblages. For the most part, the distribution of the morphotypes is reflected in the sedimentary archive, thus proving their potential as paleoecological proxies.     

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.     

Long-term upwelling evolution in tropical and equatorial Pacific during the last 800 kyr as revealed by coccolithophore assemblages

The coccolithophore assemblages in two ODP Sites (1237 and 1238) are studied in order to reconstruct the paleoenvironmental conditions in the tropical and equatorial Pacific during the last 800 kyr. Both ODP Sites are located in the two most significant upwelling zones of the tropical and equatorial Pacific: Peru and Equatorial upwelling, respectively. The two sites are considered to have had similar evolutions. The coccolith relative abundance, the nannofossil accumulation rate (NAR) and the N ratio (namely, the proportion of < 3 μm placoliths in relation to Florisphaera profunda) allow us to identify three different intervals. Interval I (0.86-0.45 Ma) and interval III (0.22-0 Ma) are related to weak upwelling and weak Trade Winds, as suggested by coccolithophore assemblages with low N ratios. Interval II (0.45-0.22 Ma), characterized by dominant Gephyrocapsa caribbeanica and very abundant “small” Gephyrocapsa and Gephyrocapsa oceanica, is conversely related to intense upwelling and enhanced Trade Winds.     

Integrative Approach Helps Clarify Confusing Taxonomy of the Pseudopediastrum boryanum Species Complex (Chlorophyceae), Including Recognition of five Distinct Species

Sixteen monoclonal strains classified into six morphotypes typical of, or close to, intraspecific taxa of Pseudopediastum boryanum, including P. alternans (ALT), P. boryanum var. boryanum (BOR), P. boryanum var. cornutum (COR), P. boryanum var. forcipatum (FOR), P. boryanum var. longicorne (LON), and P. boryanum var. perforatum (PER), were simultaneously subjected to phylogenetic (26S rDNA and rbcL cpDNA) and morphometric analyses. Marginal cell shape, coenobium and cell size, and granule density on the cell surface were analyzed statistically. The shapes of some morphotypes (BOR, COR, FOR, and PER) were also compared to the shapes of corresponding type illustrations. Pseudopediastrum boryanum var. boryanum, without any reliable morphological and phylogenetic data, appeared to be a questionable taxon that needs a neotype. The variety longicorne proved to be a complex taxon that should be split after morphometric data of more strains and of the corresponding lectotype are included in the statistical analysis. A new species, Pseudopediastrum oblongum, was described, and four varieties were elevated to the species level, which resulted in establishing new combinations, P. cornutum, P. forcipatum, P. perforatum, and P. subgranulatum. Reference sequences for the new species and combinations were obtained. The paleoecological value of P. boryanum sensu lato appeared to be limited by the relatively low percentage of marginal cells typical of particular varieties and a high risk of their misidentification in the light microscope. The shape of marginal cells seemed to be the best diagnostic feature. Granule density could be helpful to discriminate between certain taxa.     

Size analyses of the coccolith species Biscutum constans and Watznaueria barnesiae from the Late Albian “Niveau Breistroffer” (SE France): taxonomic and palaeoecological implications

The size variability of the coccolith species Biscutum constans and Watznaueria barnesiae has been studied in 50 samples of the Late Albian “Niveau Breistroffer” black shales (Col de Palluel section, SE France). For each species, length and width of the total coccolith and the central unit have been measured in 60 specimens per sample. In addition, ellipticity and central unit length/total coccolith length ratio have been calculated. This study aims to improve our understanding of the taxonomic concepts of B. constans and W. barnesiae, and to test whether the size changes correspond to palaeoceanographic changes interpreted from other proxies. Two morphotypes (varieties) were differentiated for each of the two taxa studied. B. constans includes morphotypes with a narrow (B. constans var. constans) and a wide central unit (B. constans var. ellipticum). Between these two morphotypes no significant size differentiation has been observed. They seem to represent end members of a size continuum, relating to both the total coccolith- and central unit size distribution. The two morphotypes of W. barnesiae differ only in the absence (W. barnesiae var. barnesiae) and the presence of a narrow central opening (W. barnesiae var. fossacincta). No significant size differences have been observed between these two morphotypes, and both show similar distributions of the measured characteristics. We recommend that the studied morphotypes of both B. constans and W. barnesiae should not be assigned to different morphospecies. Throughout the studied black shale succession the measured parameters show mostly statistically insignificant, short-term fluctuations, but significant long-term trends have been observed for B. constans. These show a trend to smaller forms with a narrower central unit in the upper part of the succession. This change coincides with a cooling trend, as indicated by a nannofossil based temperature index. Therefore the two morphotypes of B. constans are interpreted to represent ecophenotypic varieties rather than two different morphospecies. No clear relationship has been recognized between the size of W. barnesiae and the palaeoenvironmental conditions.     

Geographical and seasonal differences in morphology and dynamics of the coccolithophore Calcidiscus leptoporus

Calcidiscus leptoporus is a cosmopolitan coccolithophore species, composed of three morphotypes characterised by differences in morphology and size. The seasonal dynamics of this species have been studied in four sediment trap and plankton time series covering different biogeographic settings. Investigated parameters were: variations in absolute and relative abundances of the three morphotypes, average size variations of the C. leptoporus assemblages, and intra-morphotype size variations. For each time series, and for the complete data set, the relationship between C. leptoporus dynamics and some environmental parameters was investigated. Seasonal variations can be recognised in the four time series, but the biogeographic pattern governing this seasonality is complex. The two best documented morphotypes show comparable seasonal fluctuations in absolute abundances, mainly co-varying with temperature and related factors such as water mixing. However, their relative abundances change with varying nutrient contents in the surface water masses, suggesting slight differences in their respective ecological preferences. Average size of the C. leptoporus assemblage provides information about the morphotype composition and allows a comparison of the seasonal variations observed in the present study and Holocene geographic patterns reported in the literature. Additionally, intra-morphotype size variations might be related to environmental changes.     

Coccolith evidence for Quaternary nutricline variations in the southern South China Sea

Nutricline variations during the last 1560 ka in the southern South China Sea are reconstructed using the relative abundance of the coccolithophore Florisphaera profunda in ODP Site 1143. Nutricline depth shows both long-term large magnitude variation and high frequency glacial–interglacial variation. On the long-term scale, the nutricline experienced four significant changes, which occurred at 900, 480, 250, and 50 ka respectively. According to these changes, five stages could be recognized during the last 1560 ka. From 1560 to 900 ka, the nutricline depth increased gradually. Around 900 ka, the nutricline abruptly shallowed and then remained stable until 480 ka. The nutricline was shallow during the time interval between 480 and 250 ka. At 250 ka, it deepened again and increased gradually until 50 ka. After 50 ka, the nutricline depth decreased gradually to modern values. On the glacial–interglacial scale, the variations in nutricline depth show different patterns before and after 900 ka. Before 900 ka, the nutricline was deep during glacial periods and shallow during interglacials. However, after 900 ka, the nutricline was deep during interglacials and shallow during glacials. Spectral analysis of the relative abundance of F. profunda shows a similar trend. In addition to the eccentricity (113, 76 ka), obliquity (55, 39 ka), and precession (24, 19 ka), we also find a 431 ka cycle. The former three periods reflect glacial–interglacial variations in nutricline, and the period of 431 ka reflects long-term variations in nutricline. We suggested that the variations in nutricline in the southern South China Sea were caused by global and regional climate changes. Glacial–interglacial variations in nutricline are mainly controlled by the East Asian monsoon, and the long-term variations might be related to the global climatic events, such as the mid-Pleistocene Revolution and the mid-Brunhes event.     

Intra- and infra-specific morphological variation in selected coccolithophore species in the equatorial and subequatorial Pacific Ocean

The ecological preferences of morphological groups within major coccolithophore taxa were studied in surface water samples from the equatorial and subequatorial Pacific Ocean. Emiliania huxleyi was subdivided into three morphological groups: Type A, Type C, and variety corona. The most probable factors limiting the occurrence of E. huxleyi Types A and C were high temperatures and low nutrient concentrations, respectively. E. huxleyi var. corona had an affinity for oligotrophic conditions. Calcidiscus leptoporus ssp. small was adapted to fertile waters. Umbilicosphaera foliosa and Umbilicosphaera sibogae preferred mesotrophic upwelling waters and stratified marginal waters surrounding the upwelling front, respectively. Among the three Umbellosphaera tenuis morphotypes observed in this study (Types I, III, and IV), only Type I was found in very warm tropical surface. Both Types III and IV were found in subtropical waters, and Type III differed from Type IV in that its distribution was constrained to hemi-pelagic waters. Habitat segregation among the morphotypes of major taxa indicates that the observed global distributions of these major taxa are, in fact, combinations of discrete morphological groups.     

NEW EVIDENCE FOR MORPHOLOGICAL AND GENETIC VARIATION IN THE COSMOPOLITAN COCCOLITHOPHORE EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) FROM THE COX1b‐ATP4 GENES1

Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler is a cosmopolitan coccolithophore occurring from tropical to subpolar waters and exhibiting variations in morphology of coccoliths possibly related to environmental conditions. We examined morphological characters of coccoliths and partial mitochondrial sequences of the cytochrome oxidase 1b (cox1b) through adenosine triphosphate synthase 4 (atp4) genes of 39 clonal E. huxleyi strains from the Atlantic and Pacific Oceans, Mediterranean Sea, and their adjacent seas. Based on the morphological study of culture strains by SEM, Type O, a new morphotype characterized by coccoliths with an open central area, was separated from existing morphotypes A, B, B/C, C, R, and var. corona, characterized by coccoliths with central area elements. Molecular phylogenetic studies revealed that E. huxleyi consists of at least two mitochondrial sequence groups with different temperature preferences/tolerances: a cool‐water group occurring in subarctic North Atlantic and Pacific and a warm‐water group occurring in the subtropical Atlantic and Pacific and in the Mediterranean Sea.     

MORPHOLOGICAL VARIABILITY OF EUNOTIA PECTINALIS (BACILLARIOPHYCEAE) IN A SOFTWATER RHODE ISLAND STREAM AND IN CULTURE1

The diatom Eunotia pectinalis (O. F. Müll.?) Rabh. exhibited considerable morphological variability in samples collected over a 13-month period from a softwater Rhode Island stream. All observed morphotypes were classified into three main complexes based upon their valve configuration. These groupings were confirmed by discriminant analysis using quantitative valve characteristics and were named in accordance with their associated varieties: minor (Kütz.) Rabh., pectinalis and ventricosa Grun. Clonal cultures were subjected to a defined series of temperatures, agitation rates and light intensities in order to assess inherent morphological variability. Similar trends were evident for all complexes. Over time, valve length decreased, valve breadth enlarged, and striae number per 10 μm at valve center and apex increased. Morphological plasticity was evident in culture and appeared to be more a function of the clone genotype than the environmental conditions to which it was subjected. One clone originally identified as E. pectinalis var. minor assumed certain morphological features of E. vanheurckii Patr. after four months in culture.     

Coccolith distribution patterns in surface sediments of Equatorial and Southeastern Pacific Ocean

This study aims to contribute to a more detailed knowledge of the biogeography of coccolithophores in the Equatorial and Southeastern Pacific Ocean. Census data of fossil coccoliths are presented in a suite of core-top sediment samples from 15°N to 50.6°S and from 71°W to 93°W. Following standard preparation of smear slides, a total of 19 taxa are recognized in light microscopy and their relative abundances are determined for 134 surface sediment samples. Considering the multivariate character of oceanic conditions and their effects on phytoplankton, a Factor Analysis was performed and three factors were retained. Factor 1, dominated by Florisphaera profunda and Gephyrocapsa oceanica, includes samples located under warm water masses and indicates the occurrence of calcite dissolution in the water column in the area offshore Chile. Factor 2 is related to cold, low-salinity surface-water masses from the Chilean upwelling, and is dominated by Emiliania huxleyi, Gephyrocapsa sp. < 3 μm, Coccolithus pelagicus and Gephyrocapsa muellerae. Factor 3 is linked to more saline, coastal upwelling areas where Calcidiscus leptoporus and Helicosphaera carteri are the dominant species.     

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.     

Morphological Phylogenetic Analysis of Seven Varieties of Ficus deltoidea Jack from the Malay Peninsula of Malaysia

This study is the first report to suggest a morphological phylogenetic framework for the seven varieties of Ficus deltoidea Jack (Ficus: Moraceae) from the Malay Peninsula of Malaysia. Several molecular-based classifications on the genus Ficus had been proposed, but neither had discussed the relationship between seven varieties of F. deltoidea to its allies nor within the varieties. The relationship between seven varieties of F. deltoidea is still debated due to the extreme morphological variabilities and ambiguous boundaries between taxa. Thus, the correct identification of these varieties is important as several morphological characters are variety-specific. To test the monophyly and further resolved the relationship in F. deltoidea, a morphological phylogenetic analysis was conducted based on herbarium specimens representing the seven varieties of F. deltoidea that were collected from the Malay Peninsula of Malaysia, by using related species of the genus Ficus; F. grossularioides, F. ischnopoda and F. oleifolia as the outgroups. Parsimony and neighbour-joining analyses indicated that F. deltoidea is monophyletic, in that the seven varieties of F. deltoidea nested into two clades; clade subspecies deltoidea (var. deltoidea, var. bilobata, var. angustifolia, var. kunstleri and var. trengganuensis) and clade subspecies motleyana (var. intermedia and var. motleyana).     

TAXONOMIC REVISION OF THE DINOFLAGELLATE AMPHIDOMA CAUDATA: TRANSFER TO THE GENUS AZADINIUM (DINOPHYCEAE) AND PROPOSAL OF TWO VARIETIES,BASED ON MORPHOLOGICAL AND MOLECULAR PHYLOGENETIC ANALYSES1

The systematic position of Amphidoma caudata Halldal within the genus Amphidoma has remained uncertain as a result of its plate formula and the absence of molecular phylogenetic data. Also, this thecate dinoflagellate taxon has been used to designate two distinct morphotypes. The present study aims to clarify the generic affiliation of Amphidoma caudata and the taxonomic value of two different morphotypes M1 and M2. The new examination of the plate formula using SEM showed that it was the same for both morphotypes and that it corresponded to the tabulation of the recent erected genus Azadinium Elbrächter et Tillmann. Morphometric analysis, using cell size, length of apical projection in conjunction with the cell length, and the ratio of horn and spine showed that M1 and M2 formed two distinct groups. These results were supported by a molecular approach, revealing notable differences in the sequences of LSU rDNA and ITS region between these two morphotypes. Phylogenetic analyses inferred either from LSU and combined SSU, ITS region and COI data positioned M1 and M2 in a sister cluster of Azadinium species while Amphidoma languida Tillmann, Salas et Elbrächter, the only species of Amphidoma for which sequence data were available, was situated in a basal position of the Azadinium clade. Thus, we propose the transfer of Amphidoma caudata to the genus Azadinium and, consequently, the rehabilitation of the original tabulation of the genus Amphidoma Stein. To discriminate the two morphotypes, we propose a rank of variety with the following designations: Azadinium caudatum var. caudatum and Azadinium caudatum var. margalefii.     

Karyomorphological study of the Spiraea japonica complex (Rosaceae)

Reported in this paper is a karyomorphological study on one natural population of each of eight varieties in theSpiraea japonica complex. The interphase and mitotic prophase can be classified into the simple chromocenter type and the proximal type, respectively. The metaphase karyotypes of the eight varieties were formulated as follows:S. japonica var.japonica: 2n=18=14m+2sm+2st;S. japonica var.acuta: 2n=18=11m+4sm+3st;S. japonica var.incisa: 2n=18=12m+4sm+2st;S. japonica var.stellaris: 2n=18=15m+1sm+2st;S. japonica var.acuminata: 2n=18=14m+2sm+2st;S. japonica var.ovalifolia: 2n=18=10m+2sm+2st+4t;S. japonica var.glabra: 2n=18=10m+4sm+4st;S. japonica var.fortunei: 2n=36=17m+16sm+3st. Karyomorphological study reveals that the chromosome numbers within the complex are stable, and that karyomorphological divergence between the varieties lies mainly in chromosome size and organization. Based on the karyomorphological data and geographical distribution of the complex, the differentiation pattern as well as evolutionary mechanism of the complex is evaluated.     

The taxonomy,phytogeography and conservation of the Fissidens flora of Singapore,with one new species,F. pseudoceylonensis

Abstract

The Fissidens flora of Singapore has been investigated and shown to consist of 16 species, including one new species, F. pseudoceylonensis . F. crispulus var. robinsonii is proposed as a new combination and two taxa (F. mittenii var. javensis M.Fleisch. and F. ceylonensis ssp. simplex M.Fleisch.) are reduced to synonyms of F. pellucidus Hornsch. and F. ceylonensis Dozy & Molk. respectively. The biodiversity of Singapore's Fissidens flora is compared with that of Peninsular Malaysia and Pulau Tioman and the ecological and conservation implications are discussed.     

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.     

The influence of genetic background on resistance to the cabbage aphid (Brevicoryne brassicae) in Kale (Brassica oleracea var. acephala)

Resistance to Brevicoryne brassicae has been identified in the progeny of two selected kale (B. oleracea var. acephala) plants, one from the F1 hybrid cultivar ‘Arsis RS’ and one from the landrace ‘Butzo’. These plants were crossed with susceptible B. oleracea morphotypes that have different periods to flowering. The type of susceptible plant line used had an effect on the resistance phenotypc of the progeny. Tested F2 populations derived from these crosses show that resistance is not under simple genetic control. This, in addition to variation in aphid numbers within accessions, suggests that separation of genetic components of control from environmental ‘noise’ for any accession may only be possible by the production of double haploid plant lines.