James M. Ehrman

Eucampia Index as an indicator of the Late Pleistocene oscillations of the winter sea-ice extent at the ODP Leg 119 Site 745B at the Kerguelen Plateau

A new paleoenvironmental proxy, Eucampia Index, was used to trace the Late Pleistocene oscillations of winter ice extent at ODP Leg 119, Site 745B (59° 35.71′ S and 85° 51.60′ E) on the Kerguelen Plateau. The index is calculated as the ratio of winter terminal to intercalary valves of the diatom Eucampia antarctica sensu lato. During the early Brunhes the winter sea-ice edge was positioned south from Site 745. It started expanding northward, closer to the site location soon after 0.4 Ma and progressed in a manner of a several wide oscillations. For approximately the last 0.1 Ma the winter sea-ice edge oscillated less and retained similar range of oscillations. The ice edge oscillated in periods which correspond closely to that of Milankovitch oscillations of Earth obliquity, although the significance of individual periods appears to vary in time.

Cryptic diversity in a cosmopolitan diatom known as Asterionellopsis glacialis (Fragilariaceae): Implications for ecology, biogeography, and taxonomy

PREMISE OF THE STUDY Diatoms have long been known as the most species-rich of algal groups, with a wide range of estimates for species number (20-200 k) due to differing species concepts. The fine valve structure in Asterionellopsis glacialis, a diatom believed cosmopolitan and eurytopic, has never been systematically examined using modern microscopy and is an excellent candidate to genetically test morphology-based conspecificity among its geographically distant culture isolates. METHODS Isolates from the Atlantic and Pacific Oceans that were morphologically delineated as A. glacialis were genetically characterized using three nuclear DNA regions (two 18S rDNA fragments and ITS region) and one plastidal (rbcL) and one mitochondrial gene (cox1) and related to SEM-based morphometrics. KEY RESULTS Five genetically distinct groupings were found, four of which are new to science. ITS2 RNA transcript secondary structure was species specific as were plastidal and mitochondrial genes, while the 18S gene fragments did not diverge sufficiently to segregate new species efficiently. We genetically circumscribed the A. glacialis epitype. CONCLUSIONS The morphological diversification of the species examined in this study lags behind their genetic divergence. The currently accepted 2% cutoff level of operational taxonomic unit (OTU) clustering in 18S rDNA environmental sequencing is too high to recognize genetic diversity in Asterionellopsis and very likely in many other species. Our results support the notion that a considerable number of species and diversity remain to be discovered among diatoms and that species number may be more in line with higher estimates. Molecular signatures of the species discovered here will aid in their globally consistent identification and ultimate understanding of their ecology.

Diatoms from two macro-tidal mudflats in Chignecto Bay, Upper Bay of Fundy, New Brunswick, Canada

Mudflat research is dispersed among several fields (ecology, sedimentology), each with its own focus and methodology. Consequently, although the volume of mudflat literature is considerable, our understanding of mudflat ecology remains fragmented. For example, little is known about the structure of microbial communities outside Western Europe. Here we present the first North American specific composition and densities of live mudflat diatoms and relate them to properties of their environment on two closely located flats. The two flats (Daniel’s and Buck’s) were similar until the mid–1980s. After this time the biological and sedimentary environment on Buck’s Flats began to change and resulted in a precipitous decline of the keystone invertebrate Corophium volutator (Pallas). The specific diatom composition on each of the two flats examined was still very similar. Tychoplanktonic diatoms were numerically dominant on both flats. The flats differed significantly in the relative contribution of epipelic diatoms, which were about an order of magnitude greater on Buck’s Flats. CCA analysis suggests that very few of these species exist within their optimal habitat. Some of the differences appeared small, but were statistically and biologically significant. Daniel’s Flats sediments had a 30% larger mean grain size, less water and organic carbon compared to Buck’s Flats sediments. Buck’s Flats had more variable depths of the oxygenated layer, often with anoxic inclusions throughout. Daniel’s Flats supported more C. volutator, while Buck’s Flats contained greater densities of diatoms. The importance of preserving environmental conditions (sedimentary and biotic) prevailing on flats such as Danielȁ9s Flat in order to foster populations of Corophium at a level necessary to support foraging migratory shorebirds is also discussed.

Sex cells and reproduction in the diatom Nitzschia longissima (Bacillariophyta): discovery of siliceous scales in gamete cell walls and novel elements of the perizonium

I. Kaczmarskam, N.A. Davidovich and J.M. Ehrman. 2007. Sex cells and reproduction in the diatom Nitzschia longissima (Bacillariophyta): discovery of siliceous scales in gamete cell walls and novel elements of the perizonium. Phycologia 46: 726–737. DOI: 10.2216/07–04.1 We examined the fine structure of gametes and the auxospore wall in the heterothallic pennate raphid diatom Nitzschia longissima (sensu Karsten 1897). The presence of scales in the gamete wall of both sexes is demonstrated for the first time for a pennate diatom species. Silica in scales was documented by energy dispersive x-ray spectroscopy. This finding supports our earlier hypothesis that scales are present in pennate sex cells more often than previously considered and reflect their evolutionary relationship to scale-bearing ancestors. In addition, the auxospore was shown to contain both transverse and longitudinal perizonia as well as longitudinal bands with fimbriate margins. Longitudinal bands are also novel components of a pennate auxospore. All these structures are either difficult to resolve or irresolvable in light microscopy (LM), clearly demonstrating that LM is not sufficient to investigate diatom sex cell structure. The sexual process employed by N. longissima is compared to its congenerics. Unlike other species from this genus, our diatom is morphologically and behaviourally anisogamous. In addition, the copulation of gametangia is not aided by copulation tubes, papillae or copulation jellies. Therefore, sexual reproduction in N. longissima shows little similarity to that of the few other species in the genus Nitzschia thus far examined.

Phenotypic and genetic structure of interbreeding populations of the diatom Tabularia fasciculata (Bacillariophyta)

Kaczmarska I., Ehrman J.M., Moniz M.B.J. and Davidovich N. 2009. Phenotypic and genetic structure of interbreeding populations of the diatom Tabularia fasciculata (Bacillariophyta). Phycologia 48: 391–403. DOI: 10.2216/08-74.1. Diatom alpha-taxonomy heavily relies on the discontinuity in variation of species-specific structures in siliceous components of the cell wall. However, considerable intraspecific variability of valve morphology is to be expected because of the peculiar mode of diatom valve genesis during the tenure of the asexual part of the diatom life cycle. Here we evaluated variation in valve morphology among 66 Canadian and three Ukrainian clones of the diatom Tabularia fasciculata. Valve length, width, number of striae in 10 µm and number of rimoportulae per valve were enumerated for all clones. Forty-five Canadian and three Ukrainian clones were crossed and their sexual identity determined. Nuclear internal transcribed spacer 2 and 5.8S rDNA gene sequences were used to evaluate genetic variability of the clones. Our data show consistent phenotypic (at least two phenodemes ‘n’ and ‘w’) and genetic (two genodemes, ‘A’ and ‘B’) differentiation within one gamodeme (sexually compatible clones) in Canadian populations of T. fasciculata. The distribution of phenogenodemes is not continuous, even or random; a specific morphology strongly correlates a specific genotype, A and B, both members of the same gamodeme, with just a few exceptions. Specifically, width, striae density and rimoportulae number conform well (though not perfectly) to a specific genotype; only four mismatches were found among clones examined. Crimean members of the n phenodeme were morphologically and genetically very similar to those in Canada despite separation by thousands of kilometers. This is the first documented relationship between pheno- and genotype for an araphid species for which morphological, molecular and breeding data are also provided.

Auxosporulation in Paralia guyana MacGillivary (Bacillariophyta) and Possible New Insights into the Habit of the Earliest Diatoms.

Background Diatoms are one of the most ecologically important aquatic micro-eukaryotes. As a group unambiguously recognized as diatoms, they seem to have appeared relatively recently with a limited record of putative remains from oldest sediments. In contrast, molecular clock estimates for the earliest possible emergence of diatoms suggest a considerably older date. Depending on the analysis, Paralia and Leptocylindrus have been recovered within the basal molecular divergences of diatoms. Thus these genera may be in the position to inform on characters that the earliest diatoms possessed. Findings Here we present auxospore development and structure of initial and post-auxospore cells in a representative of the ancient non-polar centric genus Paralia. Their initial frustules showed unusual, but not unprecedented, spore-like morphology. Similarly, initial frustules of Leptocylindrus have been long considered resting spores and a unique peculiarity of this genus. However, even though spore-like in appearance, initial cells of Paralia readily resumed mitotic divisions. In addition, Paralia post-auxospore cells underwent several rounds of mitoses in a multi-step process of building a typical, “perfect” vegetative valve. This degree of heteromorphy immediately post-auxosporulation is thus far unknown among the diatoms. Implications A spore-related origin of diatoms has already been considered, most recently in the form of the “multiplate diploid cyst” hypothesis. Our discovery that the initial cells in some of the most ancient diatom lineages are structurally spore-like is consistent with that hypothesis because the earliest diatoms may be expected to look somewhat similar to their ancestors. We speculate that because the earliest diatoms may have appeared less diatom-like and more spore-like, they could have gone unrecognized as such in the Triassic/Jurassic sediments. If correct, diatoms may indeed be much older than the fossil record indicates, and possibly more in line with some molecular clock predictions.

Will reduced summer UV-B levels affect zooplankton populations of temperate humic and clearwater lakes?*

We collected zooplankton samples from 4×4 m enclosures located in two acidified lakes (pH<5) in Nova Scotia from June to August 1996. One lake had mean dissolved organic carbon concentrations greater than 10 mg l−1 (brown water), while the other had values between 2 and 4 mg l−1. In each lake, three enclosures were open to ambient light, while three were covered by Mylar® sheets which removed UVB and UVC wavelengths. Weekly sampling was done at all sites in July and near the end of August. Individuals were identified and the total community weighed. Analysis of results using both t-test and canonical analysis revealed small differences in populations between open and UVB covered clearwater sites in early July, but not later. There was no response of midsummer zooplankton communities in the humic lake which had a 95% extinction depth of 3 cm. In the clearwater lake (95% UVB extinction at 50 cm), the effect of radiation exclusion was relatively weak compared to most other published studies, but nevertheless statistically significant.

Haslea ostrearia-like Diatoms: Biodiversity out of the Blue

Abstract Diatoms are usually referred to as golden-brown microalgae, due to the colour of their plastids and to their pigment composition, mainly carotenoids (fucoxanthin, diadinoxanthin, diatoxanthin), which mask chlorophylls a and c . The species Haslea ostrearia Gaillon/Bory (Simonsen) appears unique because of its extraplastidial bluish colour, a consequence of the presence of a water-soluble blue pigment at cell apices, marennine. When released in seawater, marennine can be fixed on gills of oysters and other bivalves, which turn green. This greening phenomenon is economically exploited in Southwestern France, as it gives an added value to oysters. For decades, this singularity ascribed a worldwide distribution to H. ostrearia , first as Vibrio ostrearius , then Navicula ostrearia , last as H. ostrearia , when the genus Haslea was proposed by R. Simonsen (1974) . Indeed, this ‘birthmark’ (presence of blue apices) made H. ostrearia easily recognisable without further scrutiny and identification of the microalga as well as its presence easily deduced from the greening of bivalves. Consequently, the widely admitted cosmopolitan character of H. ostrearia has only been questioned recently, following the discovery in 2008, of a new species of blue diatom in the Black Sea, Haslea karadagensis . The biodiversity of blue diatoms suddenly increased with the finding of other blue species in the Mediterranean Sea, the Canary Islands, etc., the taxonomic characterization of which is in progress. This review thus focuses on the unsuspected biodiversity of blue diatoms within the genus Haslea . Methods for species determination (morphometrics, chemotaxonomy, genomics), as well as a new species, are presented and discussed.

A readily available SEM substrate for a random orientation of diatom frustules

The surface of a vinyl phonograph record was used for SEM imaging of the valves of the centric diatom Paralia Heiberg. This simple method allowed the imaging of various orientations and views of diatom valves without tilting or rotating the SEM stage. This mounting method proved to be more efficient than using traditional flat substrates such as cover slips or polycarbonate filters. Additionally, playing the phonograph record with mounted diatoms prior to SEM imaging fractured some Paralia valves and allowed the viewing of internal morphology. The use of this SEM substrate would be beneficial for other diatom species where it is difficult to match valve and face view morphology, and for species where producing different orientations of the valve is laborious.

A new blue-pigmented hasleoid diatom, Haslea provincialis, from the Mediterranean Sea

Abstract Haslea provincialis Gastineau, Hansen & Mouget, sp. nov., is a new, morphologically semicryptic blue diatom discovered on the French shores of the Mediterranean Sea. Like H. ostrearia and H. karadagensis, H. provincialis shares the capacity to synthesize a marennine-like blue pigment. Sexual reproduction between clones of H. provincialis has been repeatedly observed and resulted in viable initial cells. There were no sexual interactions with sexually competent clones of H. ostrearia or H. karadagensis, as would be expected for a separate biological species. There are strong similarities between the H. provincialis pigment and the marennine produced by H. ostrearia, evidenced by UV-visible spectrophotometry and Raman spectrometry. However, unlike the marennine from H. ostrearia, no differences were found between the extracellular and the intracellular forms of the pigment in H. provincialis. This indicates that the synthesis pathways and excretion mechanisms among the three ‘blue’ Haslea may be species-specific. Molecular taxonomy and phylogeny (based on rbcL, cox1 and SSU V4 DNA sequences) confirmed the distinct position of this species among the blue Haslea species. Haslea provincialis occurs in environments from which H. ostrearia has already been reported (mostly based on the presence of the blue cell vacuoles). Possible species misidentifications and the impact of the complex geological history of the Mediterranean Sea on blue diatom diversification are also discussed.