Search results for "Earth"
showing 10 items of 12204 documents
The use of spectral fluorescence methods to detect changes in the phytoplankton community
1998
In vivo fluorescence methods are efficient tools for studying the seasonal and spatial dynamics of phytoplankton. Traditionally the measurements are made using single excitation-emission wavelength combination. During a cruise in the Gulf of Riga (Baltic Sea) we supplemented this technique by measuring the spectral fluorescence signal (SFS) and fixed wavelength fluorescence intensities at the excitation maxima of main accessory pigments. These methods allowed the rapid collection of quantitative fluorescence data and chemotaxonomic diagnostics of the phytoplankton community. The chlorophyll a-specific fluorescence intensities (R) and the spectral fluorescence fingerprints were analysed toge…
Phytoplankton in Lake Tanganyika — vertical and horizontal distribution of in vivo fluorescence
1999
Determinations of chlorophyll a and in vivo fluorescence of photosynthetic pigments were used to study vertical and horizontal distribution of phytoplankton in Lake Tanganyika (East Africa). Blue excited fluorescence (IVFb) was an approximate predictor of chlorophyll a at different depths and locations. Green excited fluorescence (IVFg), which reflects phycoerythrin in cyanobacteria, explained chlorophyll a variation equally well, and in combination with IVFb the degree of explanation was improved to 87% (n = 90). Particularly during the shallow stratification in March–May, the maxima of chlorophyll a, IVFb and IVFg were located within the thermocline. Such distribution may have resulted fr…
Iron operates as an important factor promoting year-round diazotrophic cyanobacteria blooms in eutrophic reservoirs in the tropics
2021
Abstract We hypothesize that iron availability plays an important role in driving phytoplankton structure and dynamics in tropical reservoir. This role has often been neglected in routine monitoring of water quality since the main focus has been addressed on macronutrients such phosphorus and nitrogen. To elucidate the potential regulation exerted by iron availability on phytoplankton, a limnological investigation was carried out in two neighboring eutrophic reservoirs in tropical China. Traditional physical and chemical variables were measured along with total and dissolved iron concentrations to explore how they could influence phytoplankton structure. Statistical analyses showed that dis…
Role of potentially toxic cyanobacteria in crustacean zooplankton diet in a eutrophic lake
2019
The coexistence of potentially toxic bloom-forming cyanobacteria (CY) and generally smaller-sized grazer communities has raised the question of zooplankton (ZP) ability to control harmful cyanobacterial blooms and highlighted the need for species-specific research on ZP-CY trophic interactions in naturally occurring communities. A combination of HPLC, molecular and stable isotope analyses was used to assess in situ the importance of CY as a food source for dominant crustacean ZP species and to quantify the grazing on potentially toxic strains of Microcystis during bloom formation in large eutrophic Lake Peipsi (Estonia). Aphanizomenon, Dolichospermum, Gloeotrichia and Microcystis dominated …
Ocean Acidification and the Loss of Phenolic Substances in Marine Plants
2012
Rising atmospheric CO(2) often triggers the production of plant phenolics, including many that serve as herbivore deterrents, digestion reducers, antimicrobials, or ultraviolet sunscreens. Such responses are predicted by popular models of plant defense, especially resource availability models which link carbon availability to phenolic biosynthesis. CO(2) availability is also increasing in the oceans, where anthropogenic emissions cause ocean acidification, decreasing seawater pH and shifting the carbonate system towards further CO(2) enrichment. Such conditions tend to increase seagrass productivity but may also increase rates of grazing on these marine plants. Here we show that high CO(2) …
Effects of temperature on total phenolic compounds in Cystoseira amentacea (C. Agardh) Bory (Fucales, Phaeophyceae) from southern Mediterranean Sea
2015
The aim of this study was to test the effects of temperature on phenolic content of the brown seaweed Cystoseira amentacea. Phenolic compounds are secondary metabolites involved in different protection mechanisms as, for example, against grazers, epiphytes and UV radiation. Seasonal variations of phenolic content in C. amentacea were analysed and laboratory experiments, in which C. amentacea was exposed to an increase of temperature (25°C and 30°C), were performed. Total phenolic content (TPC) was determined colorimetrically with the Folin–Ciocalteu reagent. In C. amentacea, a seasonal pattern in TPC was observed, with a maximum value in winter-spring. C. amentacea responded significantly t…
Fine‐grain beta diversity of Palaearctic grassland vegetation
2021
QUESTIONS: Which environmental factors influence fine-grain beta diversity of vegetation and do they vary among taxonomic groups? LOCATION: Palaearctic biogeographic realm. METHODS: We extracted 4,654 nested-plot series with at least four different grain sizes between 0.0001 m² and 1,024 m² from the GrassPlot database, covering a wide range of different grassland and other open habitat types. We derived extensive environmental and structural information for these series. For each series and four taxonomic groups (vascular plants, bryophytes, lichens, all), we calculated the slope parameter (z-value) of the power law species–area relationship (SAR), as a beta diversity measure. We tested whe…
Modeling of Dead Wood Potential Based on Tree Stand Data
2020
Here we present a framework for identifying areas with high dead wood potential (DWP) for conservation planning needs. The amount and quality of dead wood and dying trees are some of the most important factors for biodiversity in forests. As they are easy to recognize on site, it is widely used as a surrogate marker for ecological quality of forests. However, wall-to-wall information on dead wood is rarely available on a large scale as field data collection is expensive and local dead wood conditions change rapidly. Our method is based on the forest growth models in the Motti forest simulator, taking into account 168 combinations of tree species, site types, and vegetation zones as well as …
Quorum Sensing and Density-Dependent Dispersal in an Aquatic Model System
2012
International audience; Many organisms use cues to decide whether to disperse or not, especially those related to the composition of their environment. Dispersal hence sometimes depends on population density, which can be important for the dynamics and evolution of subdivided populations. But very little is known about the factors that organisms use to inform their dispersal decision. We investigated the cues underlying density-dependent dispersal in interconnected microcosms of the freshwater protozoan Paramecium caudatum. In two experiments, we manipulated (i) the number of cells per microcosm and (ii) the origin of their culture medium (supernatant from high-or low-density populations). …
Growth patterns, sexual dimorphism, and maturation modeled in Pachypleurosauria from Middle Triassic of central Europe (Diapsida: Sauropterygia)
2018
Bone tissue, microanatomy, and growth are studied in humeri of the pachypleurosaurs Dactylosaurus from the early Anisian of Poland and of aff. Neusticosaurus pusillus from the Lettenkeuper (early Ladinian) of southern Germany. Histology and modeled growth curves are compared to already published data of other pachypleurosaurs. Therefore, we herein established growth curves for Anarosaurus from the middle Anisian of Winterswijk (the Netherlands) and for pachypleurosaurs from the Anisian/Ladinian of the Alpine Triassic (i.e., Neusticosaurus spp. and Serpianosaurus). Humeri of Dactylosaurus, Anarosaurus, and aff. N. pusillus, all from the Germanic Basin, usually display an inner ring of (pre-)…