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At least 271 records · Page 15Linked to original sources
PubMed1975

The ecological significance of sinking to planktonic bacteria.

Morphological and density measurements were made on planktonic bacteria from a subalpine lake. The observations were then used to predict in situ sinking rates from certain theoretical considerations. The predicted rates agreed well with observed sinking rates (on the order of 1 mm day-1). A simple analysis showed that sinking terms can be neglected in explaining distributions of unattached bacteria, except perhaps in relation to the presence of "bacterial plates."

Bacteria↗
PubMed1979

Uptake of [14C]methylammonium by plankton communities: a comparative assay for ammonium transport systems in natural waters.

A diverse range of freshwater plankton communities were tested for their ability to take up [14C]methylammonium. Uptake occurred at low substrate levels by high-affinity, energy-requiring, transport systems which were competitively inhibited by ammonium but not by L-amino acids or nicotinamide. A simple competitive inhibition model was used to examine the effects of increasing ammonium levels on uptake in a eutrophic lake. Apparent K1 values for the labelled substrate markedly increased with increasing ammonium. The transport systems had an approximately five-fold greater affinity for ammonium than for methylammonium. The Vmax for methylammonium uptake was relatively insensitive to large changes in ambient ammonium levels. This kinetic parameter may be a useful comparative measure of ammonium transport capacity in natural waters, particularly where low ambient ammonium concentrations preclude the use of 15N.

Amino Acids↗
PubMedDate not supplied

Vertical mixing and ecological effects of ultraviolet radiation in planktonic communities.

We present a mathematical model for a phytoplankton-zooplankton system, based on a predator-prey scheme. The model considers the effects of sinking in the phytoplankton, vertical mixing and attenuation of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) in the water column. In a first approach, the model was studied under conditions of average PAR irradiance and shows fluctuations and stable equilibrium points. Secondly, we introduced the effects of photoperiod and photoinhibition by UVR and vertical mixing. Under these conditions, the phytoplankton biomass oscillates depending on the combined effects of UVR and mixing. Higher inhibition by UVR and longer mixing periods can induce strong fluctuations in the system but can also produce higher plankton peaks.

Animals↗
PubMed2001

The history of eutrophication in the sea area of Helsinki in the 20th century. Long-term analysis of plankton assemblages.

The aim of this study is to present a historical continuum of nearly 100 years of environmental investigations and changes in trophic levels in the sea area of Helsinki. The survey is based on a re-examination of original planktological and meteorological data; the principle being that eutrophication can be detected in plankton assemblages despite changes in methodology. The bays around Helsinki were found to be moderately eutrophic to hypereutrophic at the beginning of the 20th century. There were considerable differences in the development of the bays both in terms of degradation and recovery. The efficiency of wastewater treatment and especially the introduction of sea outfall have played an important role in decreasing eutrophication in the bay area of Helsinki.

Animals↗
PubMed2005

Effects of fomesafen, alone and in combination with an adjuvant, on plankton communities in freshwater outdoor pond mesocosms.

Ecotoxicological effects of the diphenyl ether herbicide fomesafen, applied alone or in combination with the adjuvant Agral 90 (mixture of polyethoxylated derivatives of nonylphenol), were assessed on planktonic communities in 18-m3 outdoor mesocosms during a nine-month study. Four mesocosms were treated with fomesafen only (nominal concentration: 40 microg/L), four were treated with the mixture fomesafen-Agral 90 (nominal concentration: 40 microg/L and 90 microg/L, respectively), and four were kept as the controls. Five treatments were performed every three weeks from April 18, 2000. Mean (+/- standard error [SE]) values of fomesafen concentration in water of 62.5 (+/-5.3) and 19.4 (+/-7.6) microg/L were measured at the end of the treatment period in fomesafen- and mixture-treated mesocosms, respectively. Fomesafen, either alone or in mixture with Agral 90, had a significant positive effect on the abundance and biovolume of Cyanobacteria, Cryptophyceae, Dinophyceae, and Bacillariophyceae. Chlorophyceae were inhibited by the herbicide and laboratory toxicity tests confirmed that green algae were more sensitive toward fomesafen than other algal classes. A positive effect of treatments on phytoplankton taxonomic diversity also was observed, indicating that, like natural disturbances of intermediate strength, xenobiotics sometimes may enhance the diversity of algal communities. Fomesafen alone did not have any clear effect on zooplankton. Abundance of calanoid copepods was reduced significantly in the mixture-treated ponds, suggesting either a direct effect of the adjuvant and/or an enhancement of herbicide toxicity by Agral 90. The abundance of other zooplanktonic herbivorous groups increased due to a reduced competition for food for herbivorous species and a higher availability of preys for predators. No algal bloom was observed in the treated ponds, presumably because of grazing pressure and the low availability of nutrients.

Adjuvants, Immunologic↗
PubMed2000

The chemical defense ecology of marine unicellular plankton: constraints, mechanisms, and impacts.

The activities of unicellular microbes dominate the ecology of the marine environment, but the chemical signals that determine behavioral interactions are poorly known. In particular, chemical signals between microbial predators and prey contribute to food selection or avoidance and to defense, factors that probably affect trophic structure and such large-scale features as algal blooms. Using defense as an example, I consider physical constraints on the transmission of chemical information, and strategies and mechanisms that microbes might use to send chemical signals. Chemical signals in a low Re, viscosity-dominated physical environment are transferred by molecular diffusion and laminar advection, and may be perceived at nanomolar levels or lower. Events that occur on small temporal and physical scales in the "near-field" of prey are likely to play a role in cell-cell interactions. On the basis of cost-benefit optimization and the need for rapid activation, I suggest that microbial defense system strategies might be highly dynamic. These strategies include compartmented and activated reactions, utilizing both pulsed release of dissolved signals and contact-activated signals at the cell surface. Bioluminescence and extrusome discharge are two visible manifestations of rapidly activated microbial defenses that may serve as models for other chemical reactions as yet undetected due to the technical problems of measuring transient chemical gradients around single cells. As an example, I detail an algal dimethylsulfoniopropionate (DMSP) cleavage reaction that appears to deter protozoan feeding and explore it as a possible model for a rapidly activated, short-range chemical defense system. Although the exploration of chemical interactions among planktonic microbes is in its infancy, ecological models from macroorganisms provide useful hints of the complexity likely to be found.

Animals↗
PubMedDate not supplied

[Predators, resources, and trophic chains in the regulation of plankton population and biomass in oligothrophic lakes].

The relative strength of "top-down" versus "bottom-up" control of plankton community structure and biomass in two small oligotrophic lakes (with and without fish), located near the Polar circle (Russia), has been investigated for two years, 1996 and 1997. The comparative analyses of zooplankton biomass and species abundance showed strong negative effect of fish, stickeback (Pungitius pungitius L.), on the zooplankton community species, size structure and biomass of particular prey species but no effect on the biomass of the whole trophic level. An intensive predation in Verkhneye lake has lead to: 1) sixfold decline in biomass of large cladoceran Holopedium gibberum comparing to the lake lacking predator, 2) shift in the size mode in zooplankton community and the replacement of the typical large grazers by small species--Bosmina longirostris and rotifers. Their abundance and biomass even increased, demonstrating the stimulating effect of fish on the "inefficient" and unprofitable prey organisms. The analysis of contributions of different factors into the cladoceran's birth rate changes was applied to demonstrate the relative impact of predators and resources on zooplankton abundance. An occasional introduction of the stickleback to Vodoprovodnoye lake (the reference lake in 1996) in summer 1997 lead to drastic canges in this ecosystem: devastating decrease of zooplankton biomass and complete elimination of five previously dominant grazer species. The abundance of edible phytoplankton was slightly higher in the lake with fish in 1996 and considerably higher in the lake where fish has appeared in 1997 showing the prevailing "top-down" control of phytoplankton in oligotrophic ecosystem. The reasons of trophic cascade appearance in oligotrophic lakes are also discussed.

Animals↗
PubMedDate not supplied

[Biodiversity in plankton, benthos, and fish communities, and ecosystems of fresh water bodies with various productivity].

The species diversity of phyto- and zooplankton, benthic animals, and ichthyofauna was studied in continental water bodies that differ in type, geographic location, size, and productivity. The results showed that the number of species in the communities of aquatic organisms and in ecosystems depends on the area and volume of the water body and the level of plankton primary production. Corresponding relationships can be approximated by the equations of exponential and polymodal functions. The species number and biomass per unit area or volume proved to decrease the area or volume of the water body increased. The greatest number of heterotrophic species was observed in water bodies whose primary production approached 1400 kcal/m2 per year. It is proposed that the number of aquatic species in a body of water depends on the total area of the latter and the area of individual territories occupied by the representatives of certain species.

Algorithms↗
PubMed1975

Studies on metabolic activity of planktonic bacteria isolated from three lakes.

Studies were carried out on metabolic activity of 480 bacterial isolates on 9 substrates. All bacterial isolates studied except one utilized the casamino acids. Also with casamino acids the highest oxygen uptake values were obtained. Among the carbohydrates, glucose was most frequently utilized by the planktonic bacteria. Bacteria isolated from water of the various lakes differed in their metabolic activity as well as in the capability of utilizing the individual substrates. The capability of attacking by the bacteria the substrates applied depended largely upon the time of their isolation.

Amino Acids↗
PubMedDate not supplied

[Relationship between photosynthetic activity and assimilation of organic matter in marine plankton mixotrophic algae--the possibility of different metabolic strategies].

The relationship between photosynthetic and heterotrophic activities of plankton mixotrophic algae is characterized by the type of metabolic strategy. Algae with a primary photoautotrophic strategy grow at the expense of photosynthesis without uptake of organic substrates when inorganic and organic nutrients are available. They assimilate only organic substrates when inorganic nutrients are in shortage, while heterotrophic activity supports photosynthesis under conditions of inorganic nutrients deficiency. Algae with a primary heterotrophic strategy grow heterotrophicaly under repletion of inorganic and organic nutrients. Photosynthesis occurs only when organic substrates are depleted. The most mixotrophic algae combine the features of a primary photoautotrophic and a primary heterotrophic strategies. The varieties of metabolic types of mixotrophic algae form a continuum with a primary photoautotrophic strategy on the one end and a primary heterotrophic strategy on the other. The natural conditions allowing mixotrophic algae to use one or other metabolic strategy are determined by the dynamic of inorganic and organic nutrients.

Animals↗
PubMedDate not supplied

Ecology of planktonic heterotrophic flagellates. A review.

In aquatic environments heterotrophic flagellates are an important component within the microbial loop and the food web, owing to their involvement in the energy transfer and flux and as an intermediate link between bacteria and primary producers, and greater organisms, such as other protists and metazoan consumers. In the microbial loop heterotrophic flagellates highly contribute to fast biomass and nutrient recycling and to the production in aquatic environments. In fact, these protists consume efficiently viruses, bacteria, cyanobacteria and picophytoplankton, and are grazed mainly by other protists, rotifers and small crustaceans. In this paper the knowledge about these unicellular organisms is reviewed, taking into particular account their ecological relationships and trophic role within the plankton community of marine and freshwater environments.

Animals↗
PubMed2005

Population structure at two geographic scales in the burrowing crustacean Callichirus islagrande (Decapoda, Thalassinidea): historical and contemporary barriers to planktonic dispersal.

There has been much recent interest in the extent to which marine planktonic larvae connect local populations demographically and genetically. Uncertainties about the true extent of larval dispersal have impeded our understanding of the ecology and evolution of marine species as well as our attempts to effectively manage marine populations. Because direct measurements of larval movements are difficult, genetic markers have often been used for indirect measurements of gene flow among marine populations. Here we examine data from allozymes, mitochondrial DNA sequences, and microsatellite length polymorphisms to assess the extent of gene flow among populations of the burrowing crustacean Callichirus islagrande. All three types of markers revealed a genetic break between populations separated by the Louisiana Chenier Plain. The extent of mitochondrial sequence divergence across this break indicates that the nominal species, C. islagrande, consists of at least two lineages that have been reproductively isolated for about a million years. Within the eastern lineage microsatellite allele frequencies were significantly heterogeneous among populations as little as 10 km apart. Maximum likelihood estimates of gene flow and effective population size based on a coalescent model for the microsatellite data indicated that local populations are nearly closed. A model-based clustering method identified four or five groups from the microsatellite data, although individuals sampled from each location generally consisted of mixtures of these groups. This suggests a mechanism that would lead to genetic differentiation of open populations: gene flow from different source populations that are themselves genetically distinct.

Animals↗
PubMed1980

[Planktonic and bacterial population dynamics during experimental production of natural marine phytoplankton. II. Structure and physiology of populations and their interactions].

During the spring, an experiment was conducted on the production of natural phytoplankton in a continuous flow layout of large capacity, and an analysis was made of the simultaneous evolution of microplanktonic populations (taxonomic composition, diversity, class ranges, and energetic charge) and of bacterial populations (structure, diversity, dominances, and cetabolic potentialities). Oligotrophic initial conditions were charcterized by a poor (0.22 umg of chlorphyll a/L) and diversified (pigment diversity = 4.5) phytoplankton with nanoplanktonic dominance associated with several benthic type diatoms. Bacterial flora, in which pseudomonads were dominant (54.5%), were also diversified (Shannon index H = 3.57). Metabolic potentialities of these bacterial communities were several. Enrichment of the milieu caused the selection and development of a small number of algal species dominated by the diatoms skeletonema costatum (64 x 106/L) and Chaetoceros (3.2 x 106/L) leading to a paucispecific population with a large biomass, a pigment diversity of 1.97, and a chlorophyll a concentration of 25.08 mu/L. The bacterial community then because diversified (H = 4.12) and, although pseudomonads remained dominant (62%), a larger use of organic micromolecules was noted. The establishment of this phytoplanktonic community was followed by a zooplanktonic development in which larger species succeeded smaller ones (ciliates, tintinnides, rotifers, and copepods) corresponding to the global increase of the phytobiomass. Although this system appeared to be in a phase of relative stability, a decease in the energetic charge showed a disturbance in the physiological state of the planktonic populations. These phenomena led to the vanishing of the diatom's dominance (Chaetoceros, and then S. costatum) and its replacement by nanoplankton (123 x 106 cells/L) and dinoflagellates (300000 cells/L). A modification in the organic wealth of the milieu with the addition of particular complex material that was not or little degraded caused deep disturbances in the bacterial populations. Their diversity reached a very low level (H = 1.56 to 2.25) with a proliferation of vibrions (up to 74%) well equipped with exoenzymes, but more restricted in their nutritional versatility (marked preference for organic macromolecules). During the final phase of experimentation, despite a change in qualitative composition and a more important biomass, microplanktonic and bacterial populations returned to a diversified state nearing that of the initial conditions (pigment diversity = 3.2; H = 3.37).

Adenosine Triphosphate↗
PubMedDate not supplied

[Cestode larvae among the planktonic invertebrates of the Atlantic Ocean near the shores of Northwest Africa].

Larval cestodes were described from chaetognaths and some other planktonic animals of the north-west African coastal waters. They are species of the Trypanorhynchidea (Eutetrarhynchus sp.) and of the Tetraphyllidea (Scolex pleuronectis O. F. Müller of uni and trilocular type). Tetraphyllidea are represented also by blastocysts of the family Phyllobothriidae. Life cycles were discussed and specimens of the last group were compared to those of Rio de Janeiro.

Africa, Northern↗
PubMed1999

Carbon stable isotopes reveal complex trophic interactions in lake plankton.

The lower trophic linkages in lake plankton food webs are generally described as relatively simple, even accounting for the additional complexity of potential 'microbial looping'. Crustacean zooplankton are frequently amalgamated into one trophic functional group as grazers of autotrophic production. The carbon stable isotope ratios for separated zooplankton species, particulate organic matter (POM) and phytoplankton from a number of lakes in Finland and the UK were analysed. These revealed greater complexity in trophic interactions than would otherwise be observed if the zooplankton had been represented by a mixed sample. Grazing zooplankton were usually depleted in (13)C relative to the bulk POM on which they might feed, with (13)C deviating by up to 17 per thousand There were no consistent differences between (13)C values for copepods and cladocerans. Predatory cladocerans were generally enriched by greater than 1 per thousand compared to their putative prey. We suggest that care in separating the zooplankton species for stable isotope analysis may expose otherwise undetected sources of carbon and facilitate unravelling trophic links further up the food web. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2003

Carbon starvation survival of Listeria monocytogenes in planktonic state and in biofilm: a proteomic study.

The proteomes of Listeria monocytogenes expressed in suspension and biofilm state, in the presence and absence of a carbon source, were analysed by two-dimensional electrophoresis with the help of computer software. The up-regulated proteins in each case were identified by peptide sequencing using electrospray ionisation tandem mass spectrometry and a database search against the Listeria genome was performed. Relevant functions could be attributed to a number of the induced proteins which contribute to the understanding of the mechanisms of starvation survival of L. monocytogenes in planktonic state and in biofilm.

Amino Acid Sequence↗
PubMed1996

Effects of lindane on the planktonic community in freshwater microcosms.

Effects of lindane on natural planktonic communities were investigated in aquatic indoor microcosms. Lindane was dosed to eight 300-liter microcosms for 2 weeks, and effects and recovery processes were monitored over 12 weeks. Mean measured water concentrations of lindane during the exposure period were 3, 6, 13, 27, 55, 102, 230, and 455 micrograms/liter. Zooplankton was severely affected by lindane. The most sensitive organisms were nauplii of copepodes which were affected at all treatment levels > or = 6 micrograms/liter during exposure (Days 2-14). Recovery of nauplii abundance was concentration-dependent at concentrations < or = 55 micrograms/liter lindane, whereas at concentrations > or = 102 micrograms/liter recovery was negligible. Cladocera abundance decreased during exposure to > or = 102 micrograms/liter lindane and did not recover to original levels until the end of the study. For phytoplankton, decreased population densities of Chlorophyceae and microalgae ( < 5 microns) were observed at lindane concentrations < or = 55 micrograms/liter, where zooplankton was only temporarily affected. At higher lindane, concentrations ( > or = 102 micrograms/liter) effects on phytoplankton were not clear, as also increases in abundances were observed, probably as a consequence of minimized grazing pressure, due to high zooplankton mortality. Comparison of these results with data obtained in complex outdoor systems demonstrates the practicability and sensitivity of indoor microcosms and emphasizes the importance of long-term testing and assessment of recovery processes for prediction of environmental effects.

Animals↗
PubMed2004

A gas vesiculate planktonic strain of the purple non-sulfur bacterium Rhodoferax antarcticus isolated from Lake Fryxell, Dry Valleys, Antarctica.

A moderately psychrophilic purple non-sulfur bacterium, Rhodoferax antarcticus strain Fryx1, is described. Strain Fryx1 was isolated from the water column under the ice of the permanently frozen Lake Fryxell, Antarctica. Cells of Fryx1 are long thin rods and contain gas vesicles, the first report of such structures in purple non-sulfur bacteria. Gas vesicles are clustered at 2-4 sites per cell. Surprisingly, the 16S rRNA gene sequence of strain Fryx1 is nearly identical to that of Rfx. antarcticus strain AB, a short, vibrio-shaped phototroph isolated from an Antarctic microbial mat. Although showing physiological parallels, strains AB and Fryx1 differ distinctly in their morphology and absorption spectra. DNA-DNA hybridization shows that the genomes of strains AB and Fryx1 are highly related, yet distinct. We conclude that although strains AB and Fryx1 may indeed be the same species, their ecologies are quite different. Unlike strain AB, strain Fryx1 has adapted to a planktonic existence in the nearly freezing water column of Lake Fryxell.

Antarctic Regions↗