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[en] Camorim is a small, eutrophic reservoir in Rio de Janeiro, Brazil, with a phytoplankton community dominated most of the year by the filamentous diatom Aulacoseira spp. and the toxic cyanobacterium Cylindrospermopsis raciborskii. As filamentous species can be a poor food for grazers, we hypothesize that phytoplankton from this reservoir would constrain cladoceran fitness due to nutritional limitation and/or toxicity when animals fed mixtures of cultured green algae and natural seston. Clones of different cladoceran species were exposed either to seston from Camorim reservoir sampled in different seasons or to a C. raciborskii strain (CYLCAM-2) isolated from the reservoir. In short-term assays, cladocerans were exposed to either 100% seston or mixtures of 50% seston added to green algae (200 μg C L−1), and their survivorship and somatic growth were measured for 4 days. In life table assays, neonates were exposed to the same seston treatments over 14 days and age at first reproduction, survivorship, fecundity, total offspring, and the intrinsic rate of natural increase (r) were assessed. In general, seston negatively affected cladoceran survivorship and fitness (r), but this response was seasonally and species specific. Stronger effects of CYLCAM-2 than those caused by seston on survivorship, somatic growth, and r were found for all cladoceran species, especially when the proportion of CYLCAM-2 was higher than 50% in relation to green algae in a fixed total food concentration. Our results suggest that both nutritional (C/P and morphology) and toxicity factors can act to impair cladoceran fitness and help explain the absence of cladocerans in Camorim reservoir.
[en] The phytoplankton of Himreen reservoir was studied during Feb. 1996 to Jan 1997. A total of 98 algal species were identified, dominated by diatoms (69 apices), followed by greens (15 species), blue green algae (10 species). Diatoms was the dominants species in cell number: Navicula cryptocephala, Nitzschia palee, Cymbella affinis, and Fragillaria ulna. The number of species were difference and showed irregular seasonal variations in the studied stations.(Author)
[en] Phytoplankton are key components of ecosystems. Their growth is deeply influenced by temperature. In a context of global change, it is important to precisely estimate the impact of temperature on these organisms at different spatial and temporal scales. Here, we review the existing deterministic models used to represent the effect of temperature on microbial growth that can be applied to phytoplankton. We first describe and provide a brief mathematical analysis of the models used in constant conditions to reproduce the thermal growth curve. We present the mechanistic assumptions concerning the effect of temperature on the cell growth and mortality, and discuss their limits. The coupling effect of temperature and other environmental factors such as light are then shown. Finally, we introduce the models taking into account the acclimation needed to thrive with temperature variations. The need for new thermal models, coupled with experimental validation, is argued.
[en] We examined the effects of ultraviolet radiation (UVR) on net phosphorus (P) flux into phytoplankton communities in two boreal lakes at the Experimental Lakes Area (ELA), Canada. We manipulated P available to and irradiance received by phytoplankton during four different three-day incubations of dilution bioassays. Net P flux was estimated by measuring the accumulation of particulate P (that retained on glass fiber filters) over the incubation period. No effects of UVR on net P flux were found at ambient P levels in any of the experiments. At the highest levels of P addition, less particulate phosphorus (PP) accumulated in both the minus-UVB (∼15-40%; photosynthetically active radiation (PAR) + UVA) and full-sunlight (∼25-45%; PAR + UVA + UVB) exposed phytoplankton compared with those that received PAR only. Neither chlorophyll- nor carbon-specific net P flux was affected by UVR exposure at ambient P levels. However, at the highest levels of P enrichment, chlorophyll-specific net P flux increased in response to UVR in both lakes, whereas carbon-specific net P flux declined in one of the lakes and was unaffected by UV exposure in the second lake. Our results indicate that UVR can affect total PP accumulation in enriched systems, but not at ambient P levels, and that UVR has a weak and variable effect on biomass-specific P uptake in phytoplankton under enriched conditions. (author)
[en] In this study, we quantified the accumulation and toxicity of cadmium and copper in a freshwater green alga, Chlamydomonas reinhardtii, under different phosphate conditions. The accumulated Cd and Cu concentrations increased significantly with increasing ambient P concentrations and free metal ion concentrations. The metal:P ratio remained independent of the ambient P concentration. For the three pulse-amplitude-modulated parameters, the median inhibition concentrations were 1.5-1.6x and 2.0x higher, but the medium inhibition cellular quota was 2.2x and 1.2x lower for cells maintained at 0.1 μM P than for cells maintained at 10 μM P for Cd and Cu, respectively. Furthermore, the difference in metal toxicity decreased (for Cd) or disappeared (for Cu) when the toxicity was expressed by the metal:P ratio in the cells, indicating that the stoichiometry of metals and P can be better used to predict the toxicity of metals. It is necessary to consider the stoichiometry of metals in predicting metal toxicity in phytoplankton. - The stoichiometry of metals and P can be used to predict metal toxicity to freshwater phytoplankton under different P conditions
[en] Complete text of publication follows. Study of ocean dynamics is one of important aspects in physical and bio-geochemical oceanography because it helps to understand the mechanisms of large scale changes in ocean circulation. This research based on using of quasistationary areas (QSA) is directed on detection of global ocean currents and other dynamic processes using multi satellite data as images of Earth's electromagnetic field radiation. Method of QSA is based on the statistical treatment of seasonal composites of sea surface temperature and phytoplankton pigments concentration satellite imagery. Correlation analysis of such characteristics, sea surface temperature on the one hand and phytoplankton pigments on the other allows to reveal fundamental processes of ocean hydrology and detect global ocean currents. QSA allows to detect the location of currents and estimate changes of it boundary during time period. Using different parameters of algorithm we can reveal dynamic processes with different time and spatial scale. Another part of the research is to check a hypothesis of global thermohaline circulation. Analysis of absolute gradients of weekly sea surface temperature data allows to detect a global path of heat-and-mass transfer in the ocean. Comparison of biological and physical components of the global ocean is capable to reveal anomalous events, which are impossible to see with standard oceanological methods. Nine years of SeaWiFS satellite data from 1997-2005 were used to produce seasonal means and standard deviation estimates of chlorophyll-a concentrations for the global ocean. Seven years of MODIS imagery for 2002-2008 and twenty one years of AVHRR imagery for 1981-2001 were used to produce seasonal means and standard deviations of sea surface temperature for the global ocean. Digital map of ocean currents and oceanic frontal features was generated using QSA method. Correlation of sea surface temperature and chlorophyll concentration was estimated. Special software using IDL language for statistical treatment was developed.
[en] At present, there are few studies on the quantitative analysis of connectivity from the perspective of biocenology. This study aimed to develop a new quantitative assessment method for river connectivity based on the analysis of the effect of river connectivity on the phytoplankton community in the Shaying River, which has multiple gates. The results showed that from the view of the phytoplankton density and biomass, cryptophytes were the dominant phytoplankton group, but the cyanobacteria density was highest in the summer. In the top 10 of degrees of dominance, there were 4 species of cyanobacteria, 3 species of cryptophytes, 2 species of diatoms, and 1 species of chlorophytes. Based on the seasonal compositions and variations of the phytoplankton community, the river barriers had a great effect on the community. The community composition of the Shaying River has been transformed from a river-type community dominated by diatoms to a lake-type community dominated by cyanophytes. PCA (principal component analysis) indicated that there were obvious differences in the community structure among the sections partitioned by various river gates. According to the relative positions of the entire phytoplankton community and the relative sequence of the river gates, a potential gradient representing the river connectivity can be found; thus, the river connectivity can be quantitatively described from the perspective of the phytoplankton community, and hereby, the corresponding quantitative methods can be established. Characterizing the connectivity of rivers based on biota will facilitate assessing the effects of multiple barriers and understanding river connectivity, and provide the support for the effective management of rivers.