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Redfield revisited: variability of C[ratio ]N[ratio ]P in marine microalgae and its biochemical basis
- RICHARD J. GEIDER, JULIE LA ROCHE
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- 09 April 2002, pp. 1-17
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A compilation of data on the elemental composition of marine phytoplankton from published studies was used to determine the range of C[ratio ]N[ratio ]P. The N[ratio ]P ratio of algae and cyanobacteria is very plastic in nutrient-limited cells, ranging from <5 mol N[ratio ]mol P when phosphate is available greatly in excess of nitrate or ammonium to >100 mol N[ratio ]mol P when inorganic N is present greatly in excess of P. Under optimal nutrient-replete growth conditions, the cellular N[ratio ]P ratio is somewhat more constrained, ranging from 5 to 19 mol N[ratio ]mol P, with most observations below the Redfield ratio of 16. Limited data indicate that the critical N[ratio ]P that marks the transition between N- and P-limitation of phytoplankton growth lies in the range 20–50 mol N[ratio ]mol P, considerably in excess of the Redfield ratio. Biochemical composition can be used to constrain the critical N[ratio ]P. Although the biochemical data do not preclude the critical N[ratio ]P from being as high as 50, the typical biochemical composition of nutrient-replete algae and cyanobacteria suggests that the critical N[ratio ]P is more likely to lie in the range between 15 and 30. Despite the observation that the overall average N[ratio ]P composition of marine particulate matter closely approximates the Redfield ratio of 16, there are significant local variations with a range from 5 to 34. Consistent with the culture studies, lowest values of N[ratio ]P are associated with nitrate- and phosphate-replete conditions. The highest values of N[ratio ]P are observed in oligotrophic waters and are within the range of critical N[ratio ]P observed in cultures, but are not so high as to necessarily invoke P-limitation. The C[ratio ]N ratio is also plastic. The average C[ratio ]N ratios of nutrient-replete phytoplankton cultures, oceanic particulate matter and inorganic N and C draw-down are slightly greater than the Redfield ratio of 6·6. Neither the analysis of laboratory C[ratio ]N[ratio ]P data nor a more theoretical approach based on the relative abundance of the major biochemical molecules in the phytoplankton can support the contention that the Redfield N[ratio ]P reflects a physiological or biochemical constraint on the elemental composition of primary production.
A new combination coccosphere of the heterococcolith species Coronosphaera mediterranea and the holococcolith species Calyptrolithophora hasleana
- MARA Y. CORTÉS, JÖRG BOLLMANN
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- 09 April 2002, pp. 145-146
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This is the first description of a combination coccosphere of the heterococcolithophore species Coronosphaera mediterranea (Lohmann 1902) Gaarder in Gaarder & Heimdal (1977) and the holococcolithophore species Calyptrolithophora hasleana (Gaarder 1962) Heimdal in Heimdal & Gaarder (1980) (Figs 1, 2). A single specimen of this new combination coccosphere was found within 53000 analysed cells in one of 189 samples collected at the JGOFS time series station ALOHA, Hawaii, during 1993 to 1996. The specimen was in a sample collected during autumn 1996 at a water depth of 5 m at a temperature of 26·1 °C, salinity of 35·0 psu, phosphate of 0·002 μmol/kg and in nitrate-depleted water (for details see Cortés, 1998; Cortés et al., 2001).
Diatom aggregation in the sea: mechanisms and ecological implications
- DANIEL C. O. THORNTON
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- 16 December 2002, pp. 149-161
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Marine snow is a ubiquitous feature of the ocean and an important agent in the transport of energy and nutrients through marine ecosystems. Diatom aggregates, which form during blooms and, to a lesser extent, by the resuspension of benthic biofilms, are a primary source of marine snow. Genera commonly found in diatom aggregates are: Nitzschia, Chaetoceros, Rhizosolenia, Leptocylindricus, Skeletonema and Thalassionema. Most fieldwork has been restricted to a limited number of locations in the Northern Hemisphere. To quantify the global impact of diatom aggregation there is a need to conduct fieldwork in a wider range of areas, particularly in the Southern Hemisphere. Aggregates form when particles collide and stick together. Collisions in the water column are affected by turbulence, differential settlement and animal feeding, whereas diatom stickiness is affected by extracellular polymeric substances (EPS). Laboratory experiments have demonstrated that diatoms produce more EPS under nutrient limitation, although little is known about how limitation by different nutrients affects the quantity and composition of EPS and subsequent stickiness. EPS form three pools in the environment: cell coatings, soluble EPS and transparent exopolymeric particles (TEP). There is a need to investigate the dynamics of conversion between the pools of EPS by both abiotic and biological processes and how these conversions affect aggregate concentration and structure. Processes governing disaggregation have been largely overlooked, although they are as important as aggregation in determining the dynamics of aggregate concentrations in the water column. The biogeochemical significance of diatom aggregates as a means of transporting carbon and other nutrients from the euphotic zone to the seabed is well established. However, the internal biogeochemistry of aggregates is not well understood. Aggregates contain anaerobic microsites and further work is required to establish whether aggregates are significant sinks for nitrogen in the water column through anaerobic denitrification. Several hypotheses have been proposed to explain diatom aggregation in the field, but many of these are flawed because the mechanisms and adaptive explanations proposed require natural selection to operate at the level of populations rather than genes or individuals.
British Phycological Society Presidential Address 1999. From algal culture to ecosystem; from information to culture
- BRIAN MOSS
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- 01 August 1999, pp. 193-203
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Presidential addresses pose problems. Should one review some area or report a new piece of research; or should one be less predictable? I have chosen the latter, inspired by a BBC radio talk given by Sir Peter Medawar (1964). The talk, ‘Is the scientific paper a fraud?’, introduced a series about how scientific work is really done. Medawar, a biologist and Nobel Laureate, concluded that the scientific paper is a fraud because it misleads the reader, indeed generally lies about the making of scientific discoveries, which are usually presented as well-planned, objective, logical and dispassionate. Scientists, he wrote ‘should not be ashamed to admit, as many of them apparently are ashamed to admit, that hypotheses appear in their minds along uncharted byways of thought; that they are imaginative and inspirational in character; that they are indeed adventures of the mind.’
There followed a series of talks by the likes of Otto Frisch, Edward Bullard, Tom Cottrell and R. V. Jones which amply demonstrated Medawar's conclusions. Finally there was a summary by a historian and philosopher, J. W. N. Watkins (1964), which commented on the conventional style (‘didactic dead-pan’) of scientific papers: ‘if natural scientists … took to writing in a candid, uncensored, autobiographical way, setting out their ideas in their natural order, didactic dead-pan would gradually fall into discredit outside science too. A gratuitous barrier to mutual comprehensibility would have faded away.’ We should heed these words at a time when science has never been so successful in developing understanding of natural phenomena; but a time also when it has abysmally failed to retain public confidence, partly through alienation with its jargon, partly through the arrogance of some of its practitioners, and partly through the suspicion which harnessing of science for exploitative interests naturally brings.
I have a story to tell about how ideas have developed in understanding the role of algae in shallow freshwater ecosystems and I shall tell it in a way that Medawar and Watkins would have approved of. Recently I received a questionnaire asking me which of several things determined what research I do. It had much of the standard terminology of bureaucrat-driven management: Foresight exercise; Competitiveness; Research assessment exercise; Patents; Grant income. It was redolent with the terminology of money, power and influence, none of which have much relevance to the research I do or why I do it. I think that for me, at least, doing research is one way of understanding myself, and my needs, and therefore, possibly, the needs of others. What I do, how I do it, and how I interpret the data are functions of my past experience and of lucky opportunities that have arisen. They have little to do with forward planning and I do not believe that I am unusual in any of this.
Mechanisms of desiccation tolerance in cyanobacteria
- MALCOLM POTTS
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- 01 October 1999, pp. 319-328
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Drying of cells leads to damage resulting from crowding of cytoplasmic components, condensation of the nucleoid, increases in the Tm of membrane phase transitions, and imposition of stress upon cell walls. Prolonged desiccation leads to oxidation of proteins, DNA and membrane components through metal-dependent Fenton reactions, while Maillard reactions generate cross-linked products between the carbonyl groups of reducing sugars and the primary amines of nucleic acids and proteins. Although such damage restricts many organisms to aqueous environments, some, including many cyanobacteria, can tolerate the air-dried state for prolonged periods. Cyanobacteria in the Tintenstrich communities of exposed rock faces, Microcoleus and Lyngbya spp. in intertidal mats, chasmoendolithic Chroococcidiopsis spp. in the rocks of hot and cold deserts, and terrestrial epilithic crusts of Tolypothrix and Nostoc are examples that show a marked capacity to withstand the removal of their cellular water. For Nostoc commune, the mechanisms of desiccation tolerance reflect both simple and complex interactions at the structural, physiological and molecular levels.
Using absorbance and fluorescence spectra to discriminate microalgae
- DAVID F. MILLIE, OSCAR M. E. SCHOFIELD, GARY J. KIRKPATRICK, GEIR JOHNSEN, TERENCE J. EVENS
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- 08 October 2002, pp. 313-322
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The utility of absorbance and fluorescence-emission spectra for discriminating among microalgal phylogenetic groups, selected species, and phycobilin- and non-phycobilin-containing algae was examined using laboratory cultures. A similarity index algorithm, in conjunction with fourth-derivative transformation of absorbance spectra, provided discrimination among the chlorophyll [Chl] a/phycobilin (cyanobacteria), Chl a/Chl c/phycobilin (cryptophytes), Chl a/Chl b (chlorophytes, euglenophytes, prasinophytes), Chl a/Chl c/fucoxanthin (diatoms, chrysophytes, raphidophytes) and Chl a/Chl c/peridinin (dinoflagellates) spectral classes, and often between/among closely related phylogenetic groups within a class. Spectra for phylogenetic groups within the Chl a/Chl c/fucoxanthin, Chl a/Chl c/peridinin, Chl a/phycobilins and Chl a/Chl c/phycobilin classes were most distinguishable from spectra for groups within the Chl a/Chl b spectral class. Chrysophytes/diatoms/raphidophytes and dinoflagellates (groups within the comparable spectral classes, Chl a/Chl c/fucoxanthin and Chl a/Chl c/peridinin, respectively) displayed the greatest similarity between/among groups. Spectra for phylogenetic groups within the Chl a/Chl c classes displayed limited similarity with spectra for groups within the Chl/phycobilin classes. Among the cyanobacteria and chlorophytes surveyed, absorbance spectra of species possessing dissimilar cell morphologies were discriminated, with the greatest range of differentiation occurring among cyanobacteria. Among the cyanobacteria, spectra for selected problematic species were easily discriminated from spectra from each other and from other cyanobacteria. Fluorescence-emission spectra were distinct among spectral classes and the similarity comparisons involving fourth-derivative transformation of spectra discriminated the increasing contribution of distinct cyanobacterial species and between phycobilin- and non-phycobilin-containing species within a hypothetical mixed assemblage. These results were used to elucidate the application for in situ moored instrumentation incorporating such approaches in water quality monitoring programmes, particularly those targeting problematic cyanobacterial blooms.
Determination of microphytobenthic biomass using pulse-amplitude modulated minimum fluorescence
- CLAIRE HONEYWILL, DAVID M. PATERSON, SCOT E. HAGERTHEY
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- 18 December 2002, pp. 485-492
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Microphytobenthos are the major intertidal primary producers in many estuarine systems and assessment of their biomass is essential in ecological studies. Algal biomass can be assessed by the use of proxy measurements, e.g. chlorophyll a (Chl a), using a lengthy and destructive extraction procedure. Fluorescence is a non-destructive and in situ alternative, recently applied to microphytobenthos, using the minimum fluorescence signal (Fo) as a measurement of Chl a. In this study, Fo after 15 min of dark adaptation (Fo15) showed a significant positive correlation with Chl a (r = 0.84, p<0.001, n = 24). The relationship between Fo15 and Chl a extracted from sediment samples of increasing sample depth (0.2–2 mm) became less significant as sediment depth increased. The strongest relationship between Fo15 and Chl a, expressed as concentration (mg m−2) and content (mg kg−1), was found when all data were combined, but nearly comparable levels of association were found for in situ measurements using sediment cores up to 2.0 mm deep. Results suggested that full dark adaptation was not always achieved because a significant negative correlation was observed between Fv/Fm and ambient irradiance for seasonal data. In addition, Fo15 showed a more significant correlation with Chl a than with Fm15, suggesting some residual level of non-photochemical quenching after 15 min in the dark. Despite the incomplete dark adaptation, the highly significant relationships between Fo15 and both Chl a concentration and content suggest that the use of Fo15 is a suitable in situ proxy method of estimating algal biomass.
Diatoms, temperature and climatic change
- N. JOHN ANDERSON
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- 12 February 2001, pp. 307-314
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The development of weighted averaging models for diatoms and lake-water temperature is reviewed in relation to other factors controlling diatom abundance in lakes. It is argued that diatom–temperature models are weaker than those developed for salinity, pH and phosphorus. Moreover, even where a statistically significant model is developed for water temperature, its application over long time periods requires caution. For example, over long time periods (such as the Holocene), soil and vegetation will have changed considerably, altering lake-catchment hydrochemistry and hence the lake biota. Applications of diatom-temperature models in these instances may result in inferred temperatures that are merely artefacts of changing lake-water chemistry. However, palaeolimnological studies using variance partitioning analysis of diatom profiles in sediment cores and independent climate data show that climate signals are recorded in lake sediments. It is suggested, therefore, that the link between changing climate and diatoms be addressed via an alternative method than that of temperature-inference models. The situation demands a more complete understanding of the interactions between lake hydrodynamics and nutrient inputs from catchments over a variety of timescales.
Isolation and characterization of extracellular polysaccharides from the epipelic diatoms Cylindrotheca closterium and Navicula salinarum
- NATASCHA STAATS, BEN DE WINDER, LUCAS J. STAL, LUUC R. MUR
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- 01 May 1999, pp. 161-169
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The production and composition of extracellular polymeric substances (EPS) in axenic batch cultures of the benthic marine epipelic diatoms Navicula salinarum and Cylindrotheca closterium were investigated. EPS was secreted into the medium and the bulk was loosely associated with the cells. Neither N. salinarum nor C. closterium formed a well-defined polysaccharide capsule. EPS of both N. salinarum and C. closterium consisted predominantly of polysaccharide but small quantities of protein were present as well. EPS also contained uronic acids and SO42− groups. Analysis of monosaccharides using gas chromatography showed that for both species glucose and xylose were the main constituents, but several other monosaccharides were present in smaller quantities. Two fractions of EPS were distinguished: a small amount was secreted into the medium and a second fraction was extracted in water at 30°C. For both species the two fractions differed somewhat in composition, indicating that they represented two different types of EPS. The EPS produced by N. salinarum and by C. closterium differed in their composition. The rate of EPS production in batch culture was highest during the transition from exponential growth to stationary growth. Negatively charged groups such as uronic acids and sulphated sugars determine the adhesion capacity of EPS and probably play an important role in the stabilization of intertidal sediments on which these diatoms grow and produce biofilms.
Deep-layer autotrophic picoplankton maximum in the oligotrophic Lake Stechlin, Germany: origin, activity, development and erosion
- JUDIT PADISÁK, LOTHAR KRIENITZ, RAINER KOSCHEL, JIRÍ NEDOMA
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- 01 November 1997, pp. 403-416
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Autotrophic picoplankton (APP) abundance, primary production and vertical distribution were studied in the oligotrophic Lake Stechlin (northeastern Germany) in 1994 and 1995. Within the euphotic zone APP contributed 34% of phytoplankton biomass and 35% of primary production. Annual average APP cell number was 209×103 cells ml−1, of which 95% were unicellular cyanobacteria, 2% were colonial cyanobacteria and 3% were eukaryotes. Three ecologically and/or morphologically different groups of APP were recognized: (i) unicellular cyanobacteria belonging to the genus Cyanobium, (ii) eukaryotic species growing in early spring under isothermal conditions and (iii) cyanobacteria, partly colonial species, growing in the stratified period in the euphotic zone. Three species of eukaryotic green algae were identified: Choricystis minor, Neocystis diplococca and Pseudodictyosphaerium jurisii, the latter two being colonial. This is the first record of the occurrence of colonial eukaryotes potentially of APP size in fresh waters. In summer picocyanobacteria were highly productive so the low net increase rates indicate that losses must be high. The dominant, Cyanobium population started growing in February with maximum abundance in late April, contributing significantly to the spring peak in phytoplankton biomass. During this growth period, the population was evenly distributed in the 60 m water column. By the time the maximum biomass occurred, inorganic nutrients had decreased below analytically detectable levels. Parallel to the onset of stratification a part of the population was grazed, most probably in the microbial loop and primarily in the upper 10–15 m. The rest of the Cyanobium population accumulated in a narrow layer in the upper hypoliminon. The APP remaining from the spring was persistent for much of the summer in this cold, high-nutrient (especially nitrate)/low-light environment. Short phosphorus-turnover times suggest that APP is probably phosphate-limited. The stability of the thermocline and the pattern of thermocline development in May affected the accumulation of the APP cells in the upper hypolimnion. Thus, this process is sensitive to the physical stability of the water column.