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Gastineau R.,University of Maine, France | Davidovich N.,Ukrainian Academy of Sciences | Hansen G.,Copenhagen University | Rines J.,University of Rhode Island | And 16 more authors.
Advances in Botanical Research | Year: 2014

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. © 2014 Elsevier Ltd.


Muller M.N.,Institute for Marine and Antarctic Studies IMAS | Muller M.N.,Leibniz Institute of Marine Science | Lebrato M.,Leibniz Institute of Marine Science | Lebrato M.,University of California at San Diego | And 9 more authors.
Biogeosciences | Year: 2014

Marine calcareous sediments provide a fundamental basis for palaeoceanographic studies aiming to reconstruct past oceanic conditions and understand key biogeochemical element cycles. Calcifying unicellular phytoplankton (coccolithophores) are a major contributor to both carbon and calcium cycling by photosynthesis and the production of calcite (coccoliths) in the euphotic zone, and the subsequent long-term deposition and burial into marine sediments. Here we present data from controlled laboratory experiments on four coccolithophore species and elucidate the relation between the divalent cation (Sr, Mg and Ca) partitioning in coccoliths and cellular physiology (growth, calcification and photosynthesis). Coccolithophores were cultured under different seawater temperature and carbonate chemistry conditions. The partition coefficient of strontium (DSr) was positively correlated with both carbon dioxide (pCO2) and temperature but displayed no coherent relation to particulate organic and inorganic carbon production rates. Furthermore, DSr correlated positively with cellular growth rates when driven by temperature but no correlation was present when changes in growth rates were pCO2-induced. Our results demonstrate the complex interaction between environmental forcing and physiological control on the strontium partitioning in coccolithophore calcite and challenge interpretations of the coccolith Sr / Ca ratio from high-pCO2 environments (e.g. Palaeocene-Eocene thermal maximum). The partition coefficient of magnesium (DMg) displayed speciesspecific differences and elevated values under nutrient limitation. No conclusive correlation between coccolith DMg and temperature was observed but pCO2 induced a rising trend in coccolith DMg. Interestingly, the best correlation was found between coccolith DMg and chlorophyll a production, suggesting that chlorophyll a and calcite associated Mg originate from the same intracellular pool. These and previous findings indicate that Mg is transported into the cell and to the site of calcification via different pathways than Ca and Sr. Consequently, the coccolith Mg/ Ca ratio should be decoupled from the seawater Mg/ Ca ratio. This study gives an extended insight into the driving factors influencing the coccolith Mg/ Ca ratio and should be considered for future palaeoproxy calibrations. © Author(s) 2014.


Cubillos J.C.,Institute for Marine and Antarctic Studies IMAS | Henderiks J.,Uppsala University | Henderiks J.,University of Oslo | Beaufort L.,French National Center for Scientific Research | And 2 more authors.
Marine Micropaleontology | Year: 2012

We have adapted an existing method to estimate coccolith calcite weight using birefringence (Beaufort, 2005) to suit the large coccoliths of Coccolithus pelagicus, which are only partially birefringent under cross-polarised light microscopy. Fossil and sediment trap material from the South Tasman Rise region of the Southern Ocean was used for calibration and validation. Our approach was tested with only the coccolith central area (CA) considered for measurement, to avoid relying on the less robust proximal shields. Thus our results are relative and intend to quantify intra-specific variations in volumetric calcite weight, expressed as a Weight Index (WI). Our results were overall consistent with mass estimation based on distal shield lengths. However, the WI approach clearly has the advantage in exploring allometric scaling between coccolith size and weight, as well as in measuring the degree of calcification in similarly sized morphotypes. Combining WI and morphometry data (distal shield length, DSL), we demonstrate subtle, but statistically significant changes in shape and thus calcification degree both within and between the tested Coccolithus populations. Most strikingly, it appears that modern Coccolithus populations in the Southern Ocean are, on average, more heavily calcified than their fossil counterparts. © 2012 Elsevier B.V.


Chalot-Prat F.,University of Lorraine | Falloon T.J.,Institute for Marine and Antarctic Studies IMAS | Green D.H.,University of Tasmania | Hibberson W.O.,Australian National University
Lithos | Year: 2013

The presence of plagioclase+spinel lherzolites among ocean floor samples and in some ophiolite complexes invites speculation on their origin and relationships to processes of magmatism and lithosphere refertilisation beneath mid-ocean ridges. In an experimental approach to their petrogenesis, we have determined the compositions of liquids and co-existing minerals in the six phase assemblage [liquid+olivine+orthopyroxene+clinopyroxene+plagioclase+spinel] at 0.5GPa and 1100°C to 1200°C. In our experimental approach we maintained the olivine Mg# [Mg/(Mg+Fe)] close to 90 (i.e., 88.8-95.5) but varied plagioclase from anorthite to albite. The major variations in liquid compositions are related to plagioclase composition. Liquids have much lower MgO and FeO and higher SiO2 and Al2O3 than liquids in the 6-phase plagioclase+spinel lherzolite at 0.75GPa and 1GPa. Liquids are quartz-normative (silica-oversaturated) for plagioclase that are more calcic than An40 but nepheline-normative (critically silica-undersaturated) for plagioclase that are more sodic than An25. Liquid compositions are quite unlike natural MORB glasses with similar Mg# (i.e., compatible with parental magmas from lherzolitic mantle with Mg#≈90). Our study provides no support for models of MORB petrogenesis which suggest extraction of near-solidus melts from plagioclase lherzolite at low pressure. Similarly, referring to numerical models of melting volumes beneath mid-ocean ridges (Langmuir et al., 1992; McKenzie and Bickle, 1988) in which melt increments are calculated for different sites and these increments pooled to form MORB, our data argue that melts equilibrated with plagioclase±spinel lherzolite at <1GPa cannot be significant components of such 'pooled melt' focussed from within the melting volume. The compositions of minerals from plagioclase±spinel lherzolite at Lanzo (northern Italy; Piccardo et al., 2007) are compared with our experimental assemblages at 0.5, 0.75 and 1GPa, leading to the conclusion that the Lanzo plagioclase±spinel lherzolites equilibrated at pressures between 0.75 and 1GPa, at temperatures ~100-200°C below the solidus. Field, petrological and geochemical studies argue that the Lanzo plagioclase±spinel lherzolites are 'refertilised' by the reaction of residual harzburgite or lherzolite with percolating intergranular basaltic magma (Piccardo et al., 2007). The experimental study suggests that the process of refertilisation took place at depths of 25-30km. Our experimental data also define the co-variance of Na2O in coexisting plagioclase (An25 to An94) and clinopyroxene at 0.5 and 0.75GPa. From these data, the Na2O content of clinopyroxene can be used as a predictor for the co-existing plagioclase composition in the very common occurrences of partially serpentinised peridotite in which plagioclase is completely saussuritised. © 2013 Elsevier B.V..


Schweikert K.,University of Otago | Hurd C.L.,Institute for Marine and Antarctic Studies IMAS | Sutherland J.E.,University of Auckland | Burritt D.J.,University of Otago
Journal of Phycology | Year: 2014

It is generally accepted that ultraviolet (UV) radiation can have adverse affects on phototrophic organisms, independent of ozone depletion. The red intertidal seaweed Pyropia cinnamomea W.A. Nelson (previously Porphyra cinnamomea Sutherland et al. 2011), similar to many other intertidal macrophytes, is exposed to high levels of UV radiation on a daily basis due to emersion in the upper littoral zone. It has been shown that seaweeds, like higher plants, respond to an increased activity of antioxidative enzymes when exposed to stress. However, earlier investigations have shown that P. cinnamomea also compensates for stress due to UV radiation by increasing polyamine (PA) levels, especially bound-soluble and bound-insoluble PAs. The PA precursor putrescine (PUT) can be synthesized via two enzymatic pathways: arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). Both of these enzymes showed increased activity in P. cinnamomea under UV stress. In higher plants, ADC is the enzyme responsible for increased PA levels during stress exposure, while ODC is correlated with cell division and reproduction. However, there are contrary findings in the literature. Using two irreversible inhibitors, we identified the enzyme most likely responsible for increased PUT synthesis and therefore increased stress tolerance in P. cinnamomea. Our results show that changes in the PA synthesis pathway in P. cinnamomea under UV stress are based on an increased activity of ADC. When either inhibitor was added, lipid hydroperoxide levels increased even under photosynthetically active radiation, suggesting that PAs are involved in protection mechanisms under normal light conditions as well. We also show that under optimum or low-stress conditions, ODC activity is correlated with PUT synthesis. © 2014 Phycological Society of America.


Muller M.N.,Institute for Marine and Antarctic Studies IMAS | Muller M.N.,CNRS Oceanography Laboratory of Villefranche | Beaufort L.,Aix - Marseille University | Bernard O.,French Institute for Research in Computer Science and Automation | And 3 more authors.
Biogeosciences | Year: 2012

Coccolithophores, a key phytoplankton group, are one of the most studied organisms regarding their physiological response to ocean acidification/ carbonation. The biogenic production of calcareous coccoliths has made coccolithophores a promising group for paleoceanographic research aiming to reconstruct past environmental conditions. Recently, geochemical and morphological analyses of fossil coccoliths have gained increased interest in regard to changes in seawater carbonate chemistry. The cosmopolitan coccolithophore Emiliania huxleyi (Lohm.) Hay and Mohler was cultured over a range of ICO2 levels in controlled laboratory experiments under nutrient replete and nitrogen limited conditions. Measurements of photosynthesis and calcification revealed, as previously published, an increase in particulate organic carbon production and a moderate decrease in calcification from ambient to elevated pCO2. The enhancement in particulate organic carbon production was accompanied by an increase in cell diameter. Changes in coccolith volume were best correlated with the coccosphere/cell diameter and no significant correlation was found between the coccolith volume and the particulate inorganic carbon production. The conducted experiments revealed that the coccolith volume of E. huxleyi/I is variable with aquatic CO2 concentration but its sensitivity is rather small in comparison with its sensitivity to nitrogen limitation. Comparing coccolith morphological and geometrical parameters like volume, mass and size to physiological parameters under controlled laboratory conditions is an important step to understand variations in fossil coccolith geometry. © 2012 Author(s).


Kaiser S.,University of Hamburg | Kaiser S.,German Center for Marine Biodiversity Research | Kaiser S.,NIWA - National Institute of Water and Atmospheric Research | Kaiser S.,University of Southampton | And 41 more authors.
Marine Biology | Year: 2013

In the Southern Ocean, that is areas south of the Polar Front, long-term oceanographic cooling, geographic separation, development of isolating current and wind systems, tectonic drift and fluctuation of ice sheets amongst others have resulted in a highly endemic benthic fauna, which is generally adapted to the long-lasting, relatively stable environmental conditions. The Southern Ocean benthic ecosystem has been subject to minimal direct anthropogenic impact (compared to elsewhere) and thus presents unique opportunities to study biodiversity and its responses to environmental change. Since the beginning of the century, research under the Census of Marine Life and International Polar Year initiatives, as well as Scientific Committee of Antarctic Research biology programmes, have considerably advanced our understanding of the Southern Ocean benthos. In this paper, we evaluate recent progress in Southern Ocean benthic research and identify priorities for future research. Intense efforts to sample and describe the benthic fauna, coupled with coordination of information in global databases, have greatly enhanced understanding of the biodiversity and biogeography of the region. Some habitats, such as chemosynthetic systems, have been sampled for the first time, while application of new technologies and methods are yielding new insights into ecosystem structure and function. These advances have also highlighted important research gaps, notably the likely consequences of climate change. In a time of potentially pivotal environmental change, one of the greatest challenges is to balance conservation with increasing demands on the Southern Ocean's natural resources and services. In this context, the characterization of Southern Ocean biodiversity is an urgent priority requiring timely and accurate species identifications, application of standardized sampling and reporting procedures, as well as cooperation between disciplines and nations. © 2013 Springer-Verlag Berlin Heidelberg.


Muller M.N.,Institute for Marine and Antarctic Studies IMAS | Muller M.N.,University of Sao Paulo | Trull T.W.,University of Tasmania | Hallegraeff G.M.,Institute for Marine and Antarctic Studies IMAS
Marine Ecology Progress Series | Year: 2015

The invasion of anthropogenic carbon dioxide into the surface ocean is altering seawater carbonate speciation, a process commonly called ocean acidification. The high latitude waters of the Southern Ocean are one of the primary and most severely affected regions. Coccolithophores are an important phytoplankton group, responsible for the majority of pelagic calcium carbonate production in the world's oceans, with a distribution that ranges from tropical to polar waters. Emiliania huxleyi is numerically the most abundant coccolithophore species and appears in several different ecotypes. We tested the effects of ocean acidification on 3 carefully selected E. huxleyi ecotypes isolated from the Southern Ocean. Their responses were measured in terms of growth, photosynthesis, calcification, cellular geometry, and stoichiometry. The 3 ecotypes exhibited differing sensitivities in regards to seawater carbonate chemistry when cultured at the same temperature (14°C) and continuous light (110 μmol photons m-2 s-1). Under future ocean acidification scenarios, particulate inorganic to organic carbon ratios (PIC:POC) decreased by 38-44, 47-51 and 71-98% in morphotype A 'over-calcified' (A o/c), A and B/C, respectively. All ecotypes reduced their rate of calcification, but the cold-water adapted ecotype (morphotype B/C) was by far the most sensitive, and almost ceased calcification at partial pressure of carbon dioxide (pCO2) levels above 1000 μ atm. We recommend that future surveys for E. huxleyi cells in the Southern Ocean should include the capability of recognising 'naked cells' by molecular and microscopic tools. The distinct differences in the physiological responses of these 3 dominant Southern Ocean coccolithophore ecotypes are likely to have consequences for future coccolithophore community structures and thereby the Southern Ocean carbon cycle. © 2015 Inter-Research.


Falloon T.J.,Institute for Marine and Antarctic Studies IMAS | Falloon T.J.,University of Tasmania | Meffre S.,University of Tasmania | Crawford A.J.,University of Tasmania | And 4 more authors.
Tectonophysics | Year: 2014

The Tonga fore-arc preserves a complex history of subduction initiation, back-arc basin formation and arc volcanism which has extended from the Cretaceous to the present. In this paper, we discuss the geochemistry of a Cretaceous basalt/dolerite/gabbro suite recovered in two dredges from the Tonga fore-arc at ~ 19°S. The geochemistry of the Tonga fore-arc suite is unlike that of the uniformly depleted MORB basalts of the subducting Pacific Plate and therefore is unlikely to be accreted from Pacific Cretaceous crust. The ~ 102. Ma age obtained for one Tongan fore-arc dolerite is contemporaneous with a major phase of Cretaceous subduction-related volcanism, recorded both in detrital zircon age populations and associated volcanics from New Caledonia and New Zealand. We believe that the Tonga fore-arc basalts are a remnant of a hypothesized, once extensive Cretaceous back-arc basin, called the East New Caledonia Basin, which we propose to have existed from ~ 102 to 50. Ma. The allochthonous Poya Terrane of New Caledonia is geochemically very similar to the Tonga fore-arc basalts and represents a younger (~ 84-55. Ma) remnant of the same basin. Subduction-related Cretaceous volcanics from the SW Pacific, representing both arc and back-arc settings, all appear to have similar Zr/Nb values, suggesting a common mantle component in their petrogenesis. The Tonga fore-arc basalts are also similar to fore-arc basalts recovered from the Izu-Bonin-Mariana fore-arc, but unlike these basalts they are not associated with subduction initiation. © 2014 Elsevier B.V.


PubMed | University of Otago, University of Auckland and Institute for Marine and Antarctic Studies IMAS
Type: Journal Article | Journal: Journal of phycology | Year: 2016

It is generally accepted that ultraviolet (UV) radiation can have adverse affects on phototrophic organisms, independent of ozone depletion. The red intertidal seaweed Pyropia cinnamomea W.A. Nelson (previously Porphyra cinnamomea Sutherland etal. 2011), similar to many other intertidal macrophytes, is exposed to high levels of UV radiation on a daily basis due to emersion in the upper littoral zone. It has been shown that seaweeds, like higher plants, respond to an increased activity of antioxidative enzymes when exposed to stress. However, earlier investigations have shown that P.cinnamomea also compensates for stress due to UV radiation by increasing polyamine (PA) levels, especially bound-soluble and bound-insoluble PAs. The PA precursor putrescine (PUT) can be synthesized via two enzymatic pathways: arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). Both of these enzymes showed increased activity in P.cinnamomea under UV stress. In higher plants, ADC is the enzyme responsible for increased PA levels during stress exposure, while ODC is correlated with cell division and reproduction. However, there are contrary findings in the literature. Using two irreversible inhibitors, we identified the enzyme most likely responsible for increased PUT synthesis and therefore increased stress tolerance in P.cinnamomea. Our results show that changes in the PA synthesis pathway in P.cinnamomea under UV stress are based on an increased activity of ADC. When either inhibitor was added, lipid hydroperoxide levels increased even under photosynthetically active radiation, suggesting that PAs are involved in protection mechanisms under normal light conditions as well. We also show that under optimum or low-stress conditions, ODC activity is correlated with PUT synthesis.

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