Refine
Has Fulltext
- no (18) (remove)
Year of publication
Document Type
- Article (16)
- Doctoral Thesis (1)
- Review (1)
Language
- English (18)
Is part of the Bibliography
- yes (18)
Keywords
- phytoplankton (18) (remove)
The Fram Strait is an area with a relatively low and irregular distribution of diatom microfossils in surface sediments, and thus microfossil records are scarce, rarely exceed the Holocene, and contain sparse information about past richness and taxonomic composition. These attributes make the Fram Strait an ideal study site to test the utility of sedimentary ancient DNA (sedaDNA) metabarcoding. Amplifying a short, partial rbcL marker from samples of sediment core MSM05/5-712-2 resulted in 95.7 % of our sequences being assigned to diatoms across 18 different families, with 38.6 % of them being resolved to species and 25.8 % to genus level. Independent replicates show a high similarity of PCR products, especially in the oldest samples. Diatom sedaDNA richness is highest in the Late Weichselian and lowest in Mid- and Late Holocene samples. Taxonomic composition is dominated by cold-water and sea-ice-associated diatoms and suggests several reorganisations – after the Last Glacial Maximum, after the Younger Dryas, and after the Early and after the Mid-Holocene. Different sequences assigned to, amongst others, Chaetoceros socialis indicate the detectability of intra-specific diversity using sedaDNA. We detect no clear pattern between our diatom sedaDNA record and the previously published IP25 record of this core, although proportions of pennate diatoms increase with higher IP25 concentrations and proportions of Nitzschia cf. frigida exceeding 2 % of the assemblage point towards past sea-ice presence.
Understanding the key factors influencing the water quality of large river systems forms an important basis for the assessment and protection of cross-regional ecosystems and the implementation of adapted water management concepts. However, identifying these factors requires in-depth comprehension of the unique environmental systems, which can only be achieved by detailed water quality monitoring.
Within the scope of the joint science and sports event "Elbschwimmstaffel" (swimming relay on the river Elbe) in June/July 2017 organized by the German Ministry of Education and Research, water quality data were acquired along a 550 km long stretch of the Elbe River in Germany. During the survey, eight physiochemical water quality parameters were recorded in high spatial and temporal resolution with the BIOFISH multisensor system. Multivariate statistical methods were applied to identify and delineate processes influencing the water quality.
The BIOFISH dataset revealed that phytoplankton activity has a major impact on the water quality of the Elbe River in the summer months. The results suggest that phytoplankton biomass constitutes a substantial proportion of the suspended particles and that photosynthetic activity of phytoplankton is closely related to significant temporal changes in pH and oxygen saturation.
An evaluation of the BIOFISH data based on the combination of statistical analysis with weather and discharge data shows that the hydrological and meteorological history of the sampled water body was the main driver of phytoplankton dynamics. This study demonstrates the capacity of longitudinal river surveys with the BIOFISH or similar systems for water quality assessment, the identification of pollution sources and their utilization for online in situ monitoring of rivers.
Trait-based approaches have become increasingly successful in community ecology. They assume that the distribution of functional traits within communities responds in a predictable way to alterations in environmental forcing and that strong forcing may accelerate such trait changes. We used high frequency measurements of phytoplankton to test these assumptions. We analyzed the seasonal and long-term dynamics of the community trait mean within a multi-dimensional trait space under alternating multifactorial environmental conditions. The community trait mean exhibited a distinct recurrent annual pattern that reflected minor changes in climate, herbivory and nutrients. Independent of early spring conditions, the community trait mean was repeatedly driven into a narrow confined area in the trait space under pronounced herbivory during the clear water phase. The speed of movement was highest at the onset and the relaxation of such strong unidirectional forcing. Thus, our data support the conceptual framework of trait-based ecology that alterations in environmental conditions are systematically tracked by adjustments in the dominant functional trait values and that the speed of trait changes depends on the kind and intensity of the selection pressure. Our approach provides a sensitive tool to detect small functional differences in the community related to subtle differences in forcing.
Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P-max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes Scenedesmus quadricauda, Chlamydomonas globosa, cryptophyte Cryptomonas ovata and ochrophyte Cyclotella meneghiniana. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in S. quadricauda and Cry. ovata. Cry. ovata can be characterized as a low light-acclimated species, whereas S. quadricauda and Cyc. meneghiniana can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P-max with PUFAs and light. In S. quadricauda and Cyc. meneghiniana, PUFAs negatively affected the relationship between P-max and light. In Chl. globosa, lower light coincided with higher PUFAs and lower P-max, but PCA also indicated that PUFAs had no direct influence on P-max. PUFAs and P-max were unaffected by light in Cry. ovata. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation.
It has been proposed that growth and reproduction of animals is frequently limited by multiple nutrients simultaneously. To improve our understanding of the consequences of multiple nutrient limitations (i.e. co-limitation) for the performance of animals, we conducted standardized population growth experiments using an important aquatic consumer, the rotifer Brachionus calyciflorus. We compared nutrient profiles (sterols, fatty acids and amino acids) of rotifers and their diets to reveal consumerdiet imbalances and thus potentially limiting nutrients. In concomitant growth experiments, we directly supplemented potentially limiting substances (sterols, fatty acids, amino acids) to a nutrient-deficient diet, the cyanobacterium Synechococcus elongatus, and recorded population growth rates. The results from the supplementation experiments corroborated the nutrient limitations predicted by assessing consumerdiet imbalances, but provided more detailed information on co-limiting nutrients. While the fatty acid deficiency of the cyanobacterium appeared to be of minor importance, the addition of both cholesterol and certain amino acids (leucine and isoleucine) improved population growth rates of rotifers, indicating a simultaneous limitation by sterols and amino acids. Our results add to growing evidence that consumers frequently face multiple nutrient limitations and suggest that the concept of co-limitation has to be considered in studies assessing nutrient-limited growth responses of consumers.
Chytrids are a diverse group of ubiquitous true zoosporic fungi. The recent molecular discovery of a large diversity of undescribed chytrids has raised awareness on their important, but so far understudied ecological role in aquatic ecosystems. In the pelagic zone, of both freshwater and marine ecosystems, many chytrid species have been morphologically described as parasites on almost all major groups of phytoplankton. However, the majority of these parasitic chytrids has rarely been isolated and lack DNA sequence data, resulting in a large proportion of "dark taxa" in databases. Here, we report on the isolation and in-depth morphological, molecular and host range characterization of a chytrid infecting the common freshwater desmid Staurastrum sp. We provide first insights on the metabolic activity of the different chytrid development stages by using the vital dye FUN (R)-1 (2-chloro-4-[2,3-dihydro-3-methyl-[benzo-1,3-thiazol-2-yl]-methylidene]-1-phenylquinolinium iodide). Cross infection experiments suggest that this chytrid is an obligate parasite and specific for the genus Staurastrum sp. Phylogenetic analysis, based on ITS1-5.8S-ITS2 and 28S rDNA sequences, placed it in the order Rhizophydiales. Based on the unique zoospore ultrastructure, combined with thallus morphology, and molecular phylogenetic placement, we describe this parasitic chytrid as a new genus and species Staurastromyces oculus, within a new family Staurastromycetaceae. (C) 2017 Elsevier GmbH. All rights reserved.
Chytrids are zoosporic fungi that play an important, but yet understudied, ecological role in aquatic ecosystems. Many chytrid species have been morphologically described as parasites on phytoplankton. However, the majority of them have rarely been isolated and lack DNA sequence data. In this study we isolated and cultivated three parasitic chytrids, infecting a common volvocacean host species, Yamagishiella unicocca. To identify the chytrids, we characterized morphology and life cycle, and analyzed phylogenetic relationships based on 18S and 28S rDNA genes. Host range and specificity of the chytrids was determined by cross-infection assays with host strains, characterized by rbcL and ITS markers. We were able to confirm the identity of two chytrid strains as Endocoenobium eudorinae Ingold and Dangeardia mamillata Schroder and described the third chytrid strain as Algomyces stechlinensis gen. et sp. nov. The three chytrids were assigned to novel and phylogenetically distant clades within the phylum Chytridiomycota, each exhibiting different host specificities. By integrating morphological and molecular data of both the parasitic chytrids and their respective host species, we unveiled cryptic host-parasite associations. This study highlights that a high prevalence of (pseudo)cryptic diversity requires molecular characterization of both phytoplankton host and parasitic chytrid to accurately identify and compare host range and specificity, and to study phytoplankton-chytrid interactions in general.
Nutrient Induced Fluorescence Transients (NIFTs) have been shown to be a possible way of testing for the limiting nutrient in algal populations. In this study we tested the hypothesis that NIFTs can be used to detect a (co-)limitation for inorganic phosphorus (Pi) and CO2 in the green alga Chlamydomonas acidophila and that the magnitude of the NIFTs can be related to cellular P:C ratios. We show a co-limitation response for Pi and CO2 via traditional nutrient enrichment experiments in natural phytoplankton populations dominated by C. acidophila. We measured NIFT responses after a Pi- or a CO2-spike in C. acidophila batch cultures at various stages of Pi and inorganic C limitation. Significant NIFTs were observed in response to spikes in both nutrients. The NIFT response to a Pi-spike showed a strong negative correlation with cellular P:C ratio that was pronounced below 3 mmol P: mol C (equivalent to 0.2 pg P cell(-1)). Both cellular P and C content influenced the extent of the Pi-NIFT response. The NIFT response to a CO2-spike correlated to low CO2 culturing conditions and also had a negative correlation with cellular P content. A secondary response within the Pi-NIFT response was related to the CO2 concentration and potentially reflected co-limitation. In conclusion, NIFTs provided a quick and reliable method to detect the growth-limiting nutrient in an extremophile green alga, under Pi-, CO2- and Pi/CO2 (co-)limited growth conditions.
1. Improving the mechanistic basis of biodiversity-ecosystem function relationships requires a better understanding of how functional traits drive the dynamics of populations. For example, environmental disturbances or grazing may increase synchronization of functionally similar species, whereas functionally different species may show independent dynamics, because of different responses to the environment. Competition for resources, on the other hand, may yield a wide range of dynamic patterns among competitors and lead functionally similar and different species to display synchronized to compensatory dynamics. The mixed effect of these forces will influence the temporal fluctuations of populations and, thus, the variability of aggregate community properties.
2. To search for a relationship between functional and dynamics similarity, we studied the relationship between functional trait similarity and temporal dynamics similarity for 36 morphotypes of phytoplankton using long-term high-frequency measurements.
3. Our results show that functionally similar morphotypes exhibit dynamics that are more synchronized than those of functionally dissimilar ones. Functionally dissimilar morphotypes predominantly display independent temporal dynamics. This pattern is especially strong when short time-scales are considered.
4. Negative correlations are present among both functionally similar and dissimilar phytoplankton morphotypes, but are rarer and weaker than positive ones over all temporal scales.
5. Synthesis. We demonstrate that diversity in functional traits decreases community variability and ecosystem-level properties by decoupling the dynamics of individual morphotypes.
The importance of ciliates as herbivores and in biogeochemical cycles is increasingly recognized. An opportunity to observe the potential consequences of zooplankton dominated by ciliates arose when winter fish kills resulted in strong suppression of crustaceans by young planktivorous fish in two shallow lakes. On an annual average, ciliates made up 38-76% of the total zooplankton biomass in both lakes during two subsequent years. Consequently, ciliate biomass and their estimated grazing potential were extremely high compared with other lakes of various trophic states and depths. Grazing estimates based on abundance and size suggest that ciliates should have cleared the water column of small (<5 mu m) and intermediate (5-50 mu m) sized phytoplankton more than once a day. Especially, small feeders within the ciliates were important, likely exerting a strong top-down control on small phytoplankton. Particle-attached bacteria were presumably strongly suppressed by intermediate-sized ciliate feeders. In contrast to other lakes, large phytoplankton was proportionately very abundant. The phytoplankton community had a high evenness, which may be attributed to the feeding by numerous fast growing and selective ciliate species. Our study highlights ciliates as an important trophic link and adds to the growing awareness of the role of winter processes for plankton dynamics.