The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Ulrich Sommer - One of the best experts on this subject based on the ideXlab platform.
-
Temperature and the size of freshwater Phytoplankton
Hydrobiologia, 2020Co-Authors: Tamar Zohary, Giovanna Flaim, Ulrich SommerAbstract:We review the literature on the relationship between water temperature and size of freshwater Phytoplankton, to examine the hypothesis that freshwater Phytoplankton, like marine Phytoplankton and many other groups of organisms, conform to Bergmann’s Rule and become smaller with warming. We provide both experimental and field evidence in support of the above hypothesis, much of this evidence was hidden in studies focused on other issues, but presenting temperature and Phytoplankton size data. Freshwater Phytoplankton size shrinks with increasing temperature at both the species level (by cells or colonies becoming smaller) and at the community level (shift to smaller species). Exceptions to the Rule do occur but in most cases those exceptions can be explained by indirect effects of temperature on Phytoplankton size, via processes such as grazing or nutrient availability. With global warming, freshwater Phytoplankton are likely to be of smaller size. This article is dedicated to Colin S. Reynolds, who has had a leading role in our personal education and understanding of Phytoplankton ecology.
-
Phytoplankton response to a changing climate
Hydrobiologia, 2012Co-Authors: Monika Winder, Ulrich SommerAbstract:Phytoplankton are at the base of aquatic food webs and of global importance for ecosystem functioning and services. The dynamics of these photosynthetic cells are linked to annual fluctuations of temperature, water column mixing, resource availability, and consumption. Climate can modify these environmental factors and alter Phytoplankton structure, seasonal dynamics, and taxonomic composition. Here, we review mechanistic links between climate alterations and factors limiting primary production, and highlight studies where climate change has had a clear impact on Phytoplankton processes. Climate affects Phytoplankton both directly through physiology and indirectly by changing water column stratification and resource availability, mainly nutrients and light, or intensified grazing by heterotrophs. These modifications affect various Phytoplankton processes, and a widespread advance in Phytoplankton spring bloom timing and changing bloom magnitudes have both been observed. Climate warming also affects Phytoplankton species composition and size structure, and favors species traits best adapted to changing conditions associated with climate change. Shifts in Phytoplankton can have far-reaching consequences for ecosystem structure and functioning. An improved understanding of the mechanistic links between climate and Phytoplankton dynamics is important for predicting climate change impacts on aquatic ecosystems.
-
Cladocerans versus copepods: the cause of contrasting top–down controls on freshwater and marine Phytoplankton
Oecologia, 2006Co-Authors: Ulrich Sommer, Frank SommerAbstract:Top–down control of Phytoplankton by crustacean mesozooplankton is a cornerstone of freshwater ecology. Apparently, trophic cascades are more frequently reported from freshwater than from marine plankton. We argue that this difference is real and mainly caused by biological differences at the zooplankton–Phytoplankton link: cladocerans (particularly Daphnia ) in the lakes and copepods in the sea. We derive these conclusions from recent literature and a number of own, similarly designed mesocosm experiments conducted in a lake, a brackish water and a marine site. In all experiments, Phytoplankton were exposed to gradients of experimentally manipulated densities of zooplankton, including freshwater copepods and cladocerans, and marine copepods and appendicularians. The suggested reasons for the difference between lake and marine trophic cascades are: (1) Both copepods and cladocerans suppress only part of the Phytoplankton size spectrum: cladocerans the small and copepods the large Phytoplankton. (2) If not controlled by grazing, small Phytoplankton may increase their biomass faster than large Phytoplankton. (3) Copepods additionally release small Phytoplankton from grazing pressure by intermediate consumers (protozoa) and competitors (predation on appendicularian eggs), while cladocerans do not release large Phytoplankton from grazing pressure by any functional group. (4) Cladocerans sequester more of the limiting nutrient than copepods, leaving fewer nutrients available for compensatory growth of ungrazed Phytoplankton.
-
Complementary impact of copepods and cladocerans on Phytoplankton
Ecology Letters, 2001Co-Authors: Ulrich Sommer, Frank Sommer, Barbara Santer, Colleen Jamieson, Maarten Boersma, Claes Becker, Thomas F. HansenAbstract:The differences in the impact of two major groups of herbivorous zooplankton (Cladocera and Copepoda) on summer Phytoplankton in a mesotrophic lake were studied. Field experiments were performed in which Phytoplankton were exposed to different densities of two major types of herbivorous zooplankton, cladocerans and copepods. Contrary to expectation, neither of the two zooplankton groups significantly reduced Phytoplankton biomass. However, there were strong and contrasting impacts on Phytoplankton size structure and on individual taxa. Cladocerans suppressed small Phytoplankton, while copepods suppressed large Phytoplankton. The unaffected size classes compensated for the loss of those affected by enhanced growth. After contamination of the copepod mesocosms with the cladoceran Daphnia, the combined impact of both zooplankton groups caused a decline in total Phytoplankton biomass.
-
intermediate disturbance hypothesis in Phytoplankton ecology proceedings of the 8th workshop of the international association of Phytoplankton taxonomy and ecology held in baja hungary 5 15 july 1991
Padisak J. Reynolds C. S. and Sommer Ulrich eds. (1993) Intermediate disturbance hypothesis in phytoplankton ecology : proceedings of the 8th workshop, 1993Co-Authors: J Padisak, C S Reynolds, Ulrich SommerAbstract:Foreword. Hutchinson's heritage: the diversity-disturbance relationship in Phytoplankton U. Sommer, J. Padisak, C.S. Reynolds, P. Juhasz-Nagy. Disturbance events affecting Phytoplankton biomass, composition and species diversity in a shallow, eutrophic, temperate lake B.A. Jacobsen, P. Simonsen. Stress and disturbance in the Phytoplankton community of a shallow hypertrophic lake K. Olrik, A. Nauwerck. Diversity and succession of the Phytoplankton in a small lake over a two-year period P. Eloranta. Phytoplankton succession and diversity in a warm monomictic, relatively shallow lake: Lake Volvi, Macedonia, Greece M. Moustaka-Gouni. Hypertrophic Phytoplankton and the Intermediate Disturbance Hypothesis C. Rojo, M. Alvarez-Cobelas. Disturbance-diversity relationships in two lakes of similar nutrient chemistry but contrasting disturbance regimes U. Sommer. Importance of intermediate disturbances for species composition and diversity of Phytoplankton in two very different Berlin lakes I. Chorus, G. Schlag. Seasonal succession of Phytoplankton and its diversity in two highly eutrophic lakes with different conditions of stratification I. Trifonova. Seasonal fluctuations in the diversity and compositional stability of Phytoplankton communities in small lakes in upper Bavaria R. Holzmann. Ecology of the Phytoplankton of the River Moselle: effects of disturbances on community structure and diversity J.-P. Descy. Some notes about the Intermediate Disturbance Hypothesis and its effects on the Phytoplankton of the middle Orinoco river H.I. Carvayal-Chitty. Effects of the water discharge on periphyton abundance and diversity in a large river (River Danube, Hungary) E. Acs, K.T. Kiss. The influence of different disturbance frequencies on the species richness, diversityand equitability of Phytoplankton in shallow lakes J. Padisak. Scales of disturbance and their role in plankton ecology C.S. Reynolds. Notes on compositional diversity P. Juhasz-Nagy. Intermediate disturbance in the ecology of Phytoplankton and the maintenance of species diversity: a synthesis C.S. Reynolds, U. Sommer, J. Padisak. General index.
Jed A Fuhrman - One of the best experts on this subject based on the ideXlab platform.
-
pronounced daily succession of Phytoplankton archaea and bacteria following a spring bloom
Nature microbiology, 2016Co-Authors: David M Needham, Jed A FuhrmanAbstract:Marine Phytoplankton perform approximately half of global carbon fixation, with their blooms contributing disproportionately to carbon sequestration1, and most Phytoplankton production is ultimately consumed by heterotrophic prokaryotes2. Therefore, Phytoplankton and heterotrophic community dynamics are important in modelling carbon cycling and the impacts of global change3. In a typical bloom, diatoms dominate initially, transitioning over several weeks to smaller and motile Phytoplankton4. Here, we show unexpected, rapid community variation from daily rRNA analysis of Phytoplankton and prokaryotic community members following a bloom off southern California. Analysis of Phytoplankton chloroplast 16S rRNA demonstrated ten different dominant Phytoplankton over 18 days alone, including four taxa with animal toxin-producing strains. The dominant diatoms, flagellates and picoPhytoplankton varied dramatically in carbon export potential. Dominant prokaryotes also varied rapidly. Euryarchaea briefly became the most abundant organism, peaking over a few days to account for about 40% of prokaryotes. Phytoplankton and prokaryotic communities correlated better with each other than with environmental parameters. Extending beyond the traditional view of blooms being controlled primarily by physics and inorganic nutrients, these dynamics imply highly heterogeneous, continually changing conditions over time and/or space and suggest that interactions among microorganisms are critical in controlling plankton diversity, dynamics and fates. Rapid variation in the Phytoplankton and bacterioplankton communities of a spring bloom provides new insights into the biological and physical parameters affecting plankton succession.
-
Pronounced daily succession of Phytoplankton, archaea and bacteria following a spring bloom
Nature Microbiology, 2016Co-Authors: David M Needham, Jed A FuhrmanAbstract:Marine Phytoplankton perform approximately half of global carbon fixation, with their blooms contributing disproportionately to carbon sequestration^ 1 , and most Phytoplankton production is ultimately consumed by heterotrophic prokaryotes^ 2 . Therefore, Phytoplankton and heterotrophic community dynamics are important in modelling carbon cycling and the impacts of global change^ 3 . In a typical bloom, diatoms dominate initially, transitioning over several weeks to smaller and motile Phytoplankton^ 4 . Here, we show unexpected, rapid community variation from daily rRNA analysis of Phytoplankton and prokaryotic community members following a bloom off southern California. Analysis of Phytoplankton chloroplast 16S rRNA demonstrated ten different dominant Phytoplankton over 18 days alone, including four taxa with animal toxin-producing strains. The dominant diatoms, flagellates and picoPhytoplankton varied dramatically in carbon export potential. Dominant prokaryotes also varied rapidly. Euryarchaea briefly became the most abundant organism, peaking over a few days to account for about 40% of prokaryotes. Phytoplankton and prokaryotic communities correlated better with each other than with environmental parameters. Extending beyond the traditional view of blooms being controlled primarily by physics and inorganic nutrients, these dynamics imply highly heterogeneous, continually changing conditions over time and/or space and suggest that interactions among microorganisms are critical in controlling plankton diversity, dynamics and fates. Rapid variation in the Phytoplankton and bacterioplankton communities of a spring bloom provides new insights into the biological and physical parameters affecting plankton succession.
Trevor Platt - One of the best experts on this subject based on the ideXlab platform.
-
a three component classification of Phytoplankton absorption spectra application to ocean color data
Remote Sensing of Environment, 2011Co-Authors: Emmanuel Devred, Shubha Sathyendranath, Venetia Stuart, Trevor PlattAbstract:A method is presented to identify absorption characteristics of three optically-distinct Phytoplankton classes from a suite of measurements of total Phytoplankton absorption coefficient and chlorophyll-a concentration by successive application of the two-population absorption model of Sathyendranath et al. (2001) and Devred et al. (2006a). The total Phytoplankton absorption coefficient at multiple wavelengths is expressed as the weighted sum of the absorption coefficients of each class at those wavelengths. The resultant system of equations is solved under some constraints to derive the fraction of each class present in any given sample of seawater, given the spectrum of total Phytoplankton absorption coefficient. When applied to a large database, the results compare well with Phytoplankton size-classes derived from pigment composition, so that we can assume that the three Phytoplankton classes derived from absorption coefficients are representative of the pico-, nano- and microPhytoplankton size classes. A modification is proposed to the pigment-based Phytoplankton size classification of Uitz et al. (2006) to account for the effect of fucoxanthin associated with nanoPhytoplankton. Comparison between satellite and in situ data demonstrates the potential of satellite ocean-color data to yield the distribution of Phytoplankton size classes from space. The algorithm is applied to Phytoplankton absorption coefficients derived from remotely-sensed reflectance values collected by SeaWiFS over the Northwest Atlantic in 2007. Monthly composites for April, August and November, representative of Spring, Summer and Fall, give synoptic views of the Phytoplankton community structure: a Spring bloom dominated by microPhytoplankton is followed by a second, less intense, bloom in the Fall dominated by nanoPhytoplankton. PicoPhytoplankton are dominant in the study area in Summer.
John J Cullen - One of the best experts on this subject based on the ideXlab platform.
-
assessment of the relationships between dominant cell size in natural Phytoplankton communities and the spectral shape of the absorption coefficient
Limnology and Oceanography, 2002Co-Authors: Aurea M Ciotti, Marlon R Lewis, John J CullenAbstract:Size-fractionated chlorophyll concentration and Phytoplankton absorption spectra were compared for a wide variety of natural communities. We found that, in general, when Phytoplankton abundance increases, larger sizeclasses are added incrementally to a background of smaller cells. Natural Phytoplankton communities from surface waters were explicitly characterized according to their dominant cell size and taxonomic group, and the relationships between this classification and the spectral shape of the Phytoplankton absorption coefficient for the whole assemblage was described. By specifying the cell size of the dominant organism (pico-, ultra-, nano-, or microplankton), more than 80% of the variability in spectral shape of the Phytoplankton absorption coefficient from 400 to 700 nm could be explained. This is a result of the strong covariation of the size of dominant organisms and several factors controlling the spectral shape of the Phytoplankton absorption coefficient, such as pigment packaging and concentration of accessory pigments. Consequently, the shapes of Phytoplankton absorption spectra can be reproduced using a spectral mixing model, where two spectra, representing the normalized Phytoplankton absorption coefficients for the smallest and the largest cells found in our data set, are combined additively, using a single parameter to specify the complementary contribution of each. The differences between reproduced and measured spectra contain taxonomic and physiological information. This parameterization provides a simple tool for extracting ecological information from optical measurements. It can also be used in sensitivity analyses to describe the influence of the dominant cell size of Phytoplankton on optical properties of surface waters. Changes in Phytoplankton species composition are a central feature of marine ecosystem dynamics. Description and prediction of these changes are important goals to many fields in oceanography. In recent years, great effort has been made to understand how changes in Phytoplankton species composition can affect optical properties of surface waters (e.g., Morel 1997; Kahru and Mitchell 1998; Stuart et al. 1998; Stramski et al. 2001). A major application of these results is the use of in situ optical instruments or remote sensing to observe variability of Phytoplankton continuously or synoptically. This is a complicated topic because Phytoplankton communities include species differing in size, shape, external and internal structures, and pigment composition. All these characteristics influence their interaction with the light field to some degree, so many factors must be considered to completely describe the optical properties of different communities of Phytoplankton. A central goal is 1
Chih‐hao Hsieh - One of the best experts on this subject based on the ideXlab platform.
-
The paradox of re‐oligotrophication: the role of bottom–up versus top–down controls on the Phytoplankton community
Oikos, 2019Co-Authors: Orlane Anneville, Chun‐wei Chang, Gaël Dur, Sami Souissi, Frédéric Rimet, Chih‐hao HsiehAbstract:Increases in Phytoplankton biomass have been widely observed over the past decades, even in lakes experiencing nutrient reduction. However, the mechanisms giving rise to this trend remain unclear. Here, we unveil the potential mechanisms through quantifying the relative contribution of bottom-up versus top-down control in determining biomasses of Phytoplankton assemblages in Lake Geneva. Specifically, we apply nonlinear time series analysis, convergent cross mapping (CCM), to decipher the degree of bottom-up versus top-down control among Phytoplankton assemblages via quantifying 1) causal links between environmental factors and various Phytoplankton assemblages and 2) the relative importance of bottom-up, top-down, and environmental effects. We show that the recent increase in total Phytoplankton biomass, albeit with phosphorus reduction, was mainly caused by a particular Phytoplankton assemblage which was better adapted to the re-oligotrophicated environment characterized by relatively low phosphorus concentrations and warm water temperature, and poorly controlled by zooplankton grazing. Our findings suggest that zooplankton act as a critical driver of Phytoplankton biomass and strongly impact the dynamics of recovery from eutrophication. Therefore, our Phytoplankton assemblage approach in combination with causal identification of top-down versus bottom-up controls provides insights into the reason why Phytoplankton biomass may increase in lakes undergoing phosphorus reduction.
