Sulphur stable isotopes can distinguish trophic dependence on sediments and plankton in boreal lakes

1. Stable isotopes of carbon are useful for differentiating between freshwater food chains based on planktonic algae or benthic algae, but are reported to be of limited use for identifying food chains based on sedimentary detritus. Because data from marine systems suggest that stable isotopes of sulphur (δ³⁴S values) have potential in this regard, we tested their utility in freshwater lakes.
2. We found that sulphate in the water column of four boreal lakes was enriched in ³⁴S compared to the sulphur in bulk sediments from these lakes. Furthermore, within a given lake, insects known to feed on sediment (directly or via predation) had δ³⁴S values similar to those of sediment, whereas planktonic and benthic invertebrates known to feed on suspended particles had δ³⁴S values similar to those of sulphate in the water column.
3. Using the stable S isotope values of invertebrates that obtain their S from either the sediment or the water column as end members in a two-source mixing model, we show that two fish species obtain their food from both planktonic and sedimentary sources. Furthermore, model results suggest that, as expected, the more benthic-feeding fish species obtains more of its S from the sediment compartment than does the species that feeds in the water-column.
4. Our results suggest that measurements of stable sulphur isotopes provide a means of distinguishing between members of food chains that are based in the water column from those based on sedimentary detritus. As such, they would be a useful complement to stable C isotopes that are used to distinguish between food chains based on planktonic or benthic algae.     

An assessment of the influence of recruitment from the sediment on the development of planktonic populations of cyanobacteria in a temperate mesotrophic lake

1. A number of planktonic cyanobacteria species form resting stages that survive in the sediments of lakes. The significance of this life history strategy to the ecology of new planktonic populations was investigated in Esthwaite Water, a mesotrophic lake in the English Lake District.
2. A simple trapping technique was used to quantify vertical movements of five species of buoyant gas-vacuolate cyanobacteria from close to the sediments, along a depth transect.
3. 'Recruitment' from the sediments was found to be widespread amongst the cyanobacteria species associated with the summer phytoplankton community.
4. Estimates of the vertical upward fluxes of cyanobacteria based upon trap catches could not account for observed increases in the planktonic populations suggesting that 'recruitment' was not a significant source of biomass.
5. Vertical upward movements of Anabaena solitaria were recorded prior to this species becoming established in the plankton suggesting that benthic populations might be a source of cells for initial pelagic growth of populations of this species.
6. Low numbers of vegetative filaments of Anabaena flos-aquae , Aphanizomenon flos-aquae and Oscillatoria agardhii were observed in the plankton through the winter. These small overwintering populations appeared to be the primary source of inocula for the large summer populations of these species.     

Spatial variations in the water quality of Lough Erne, Northern Ireland, on the basis of surface sediment diatom analysis

SUMMARY. 1. Constrained cluster analysis of thirty-five surface sediment diatom assemblages shows that Lough Erne, a complex multi-basin lake in Northern Ireland, can be sub-divided into four main zones.
2. All areas of the lake system have planktonic diatoms typical of eutrophic lakes but the lack of small Stephanodiscus species in zone 4 suggests that this area of the system is least productive.
3. Surface sediment diatom assemblages can be used to assess spatial variations in complex lake systems and can thereby be used as a guide to the choice of sites for water quality monitoring and sediment coring.     

Decapod Larvae: Dispersal, Mortality, and Ecology. A Working Hypothesis

TWO topics on decapod larval biology are discussed: retentionand recruitment of decapod larvae to the parental populationand the ecological role of decapod larvae in the water column. Most decapods have retained a planktonic larval phase whichis generally interpreted as a mechanism for increased dispersal.Evidence of restricted gene flow and biological/physical interactionresearch have suggested that larvae can be retained and recruitedto the parental population via mesoscale processes. To fullyunderstand recruitment processes improved estimates of mortalityrates for planktonic larval stages will be required. Recentevidence suggests that mortality rates are not constant overthe complete larval developmental period but decrease with time. During some seasons meroplankton including decapod l arvae canconstitute more than 50% of the plankton biomass. The quantityof energy transferred into the water column can be significant.Their role in planktonic ecology may be significant and additionalresearch is required.     

Interstitial Ciliates: Benthic Microaerophiles or Planktonic Anaerobes?

We observed marine benthic interstitial ciliates Geleia sp. and Tracheloraphis sp. inhabiting the water column of a chemically stratified salt pond. This habitat is uncharacteristic for interstitial ciliates, yet they displayed active and abundant planktonic populations (up to 800 and 250 cells/liter, respectively) and a well-defined pattern of vertical distribution. Completely absent from the oxygenated epilimnion, they first appeared at the oxic/anoxic interface and were present throughout the anoxic hypolimnion. The data could not be explained by a passive removal (e.g. by currents) of these ciliates from their conventional habitat (soft sediments) to water column. The results suggest that 1) these ciliates favored an anoxic environment, and 2) they switched to a planktonic lifestyle as appropriate conditions (seasonal anoxia) developed in the water column. This sharply contrasts the classic view of these ciliates as specifically benthic and aerobic (albeit microaerophilic) organisms. We hypothesize that Geleia sp. and Tracheloraphis sp. can readily grow in either water column or benthos, but are typically found in sediments simply because they contain their preferred (anoxic) niche.     

The efficacy of biocides and other chemical additives in cooling water systems in the control of amoebae

Aims:  In vitro experiments were undertaken to evaluate biocide formulations commonly used in cooling water systems against protozoa previously isolated from cooling towers. The investigations evaluated the efficacy of these formulations against amoebic cysts and trophozoites.
Methods and Results:  Laboratory challenges against protozoa isolated from cooling towers using chlorine, bromine and isothiazolinone biocides showed that all were effective after 4 h. The presence of molybdate and organic phosphates resulted in longer kill times for bromine and isothiazolinones. All treatments resulted in no detectable viable protozoa after 4 h of exposure.
Conclusions:  The chemical disinfection of planktonic protozoa in cooling water systems is strongly influenced by the residence time of the formulation and less so by its active constituent. Bromine and isothiazolinone formulations may require higher dosage of concentrations than currently practiced if used in conjunction with molybdate- and phosphate-based scale/corrosion inhibitors.
Significance and Impact of the Study:  Cooling water systems are complex microbial ecosystems in which predator–prey relationships play a key role in the dissemination of Legionella . This study demonstrated that at recommended dosing concentrations, biocides had species-specific effects on environmental isolates of amoebae that may act as reservoirs for Legionella multiplication in cooling water systems.     

Microbial inactivation using plasma-activated water obtained by gliding electric discharges

Aim:  To evaluate the microbial disinfection efficacy of a plasmachemical solution obtained by the activation of water with gliding electric discharges.
Methods and Results:  Distilled water was activated for 5 min by a nonthermal quenched plasma of the glidarc type operating in humid air and at atmospheric pressure. The plasma-activated water (PAW) was then used to treat planktonic and adherent cells of Staphylococcus epidermidis , Leuconostoc mesenteroides (as models of Gram-positive bacteria), Hafnia alvei (a Gram-negative bacteria) and Saccharomyces cerevisiae (as a yeast model). The treatments were less efficient on adherent cells than on planktonic cells in the case of bacteria, but not of S. cerevisiae . Inactivation was more effective for bacteria than for the yeast.
Conclusions:  Significant reductions in microbial populations were achieved in all cases, demonstrating the effectiveness of this new approach to treat contaminated media.
Significance and Impact of the Study:  PAW is a promising solution with potential application to the decontamination of equipment and surfaces.     

The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summer

SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000.
2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell⁻¹ day⁻¹ in Lake Fryxell and 0.36–11.76 bacteria cell⁻¹ day⁻¹ in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell⁻¹ h⁻¹ in Lake Fryxell and 0.074 to 1.08 pg C cell⁻¹ h⁻¹ in Lake Hoare.
3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12–21% of the community carbon budget in November and 1–28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration.
4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth.     

海洋浮游纤毛虫包囊的研究进展*

作为微型浮游动物的重要组成部分,海洋浮游纤毛虫是连接微食物环和经典食物链的重要中介。有些浮游纤毛虫在生活周期中会形成包囊,条件适宜时包囊会萌发,这对纤毛虫种群动态有重要的意义。目前国际上对于浮游纤毛虫生态学的研究主要集中在其营养期细胞,浮游纤毛虫包囊的研究尚少,中国还没有这方面的研究。本文对浮游纤毛虫包囊研究进展进行概述,包括包囊的形态、沉积物中包囊的丰度、包囊形成的环境因素、包囊萌发过程及环境因素对包囊萌发的影响等方面,希望对国内开展浮游纤毛虫包囊的研究有所裨益。     

The ecology of a subterranean isopod, Caecidotea tridentata

1. The blind isopod Caecidotea tridentata is the dominant invertebrate in a simple community of subterranean organisms inhabiting the local, shallow aquifer under Konza Prairie, Kansas, U.S.A.
2. The ecology of this karst aquifer was explored by sieving water from a spring, collecting water samples for analysis, and manipulating sediments and invertebrates in the laboratory. The size frequency distribution was stable and gravid females were present throughout the year, suggesting continuous reproduction.
3. The number of isopods collected per litre was negatively correlated with discharge and the abundance of bacteria, but positively related to the numbers of an amphipod ( Bactrurus hubrichti ). This may be explained if both the isopods and the amphipods track the saturated zone below the top of the water table; at lower discharge, the top of the water table is closer to the spring outlet. The suspended bacteria wash out in greater numbers with high discharge.
4. When isopods and carbon were added in a pairwise experimental design to sediments collected from the aquifer, the isopods significantly stimulated numbers and activity of planktonic and sedimentary bacteria, while carbon had no effect. This suggests that invertebrates can affect the microbes locally in an aquifer.     

The ecology of a subterranean isopod, Caecidotea tridentata

1. The blind isopod Caecidotea tridentata is the dominant invertebrate in a simple community of subterranean organisms inhabiting the local, shallow aquifer under Konza Prairie, Kansas, U.S.A.
2. The ecology of this karst aquifer was explored by sieving water from a spring, collecting water samples for analysis, and manipulating sediments and invertebrates in the laboratory. The size frequency distribution was stable and gravid females were present throughout the year, suggesting continuous reproduction.
3. The number of isopods collected per litre was negatively correlated with discharge and the abundance of bacteria, but positively related to the numbers of an amphipod ( Bactrurus hubrichti ). This may be explained if both the isopods and the amphipods track the saturated zone below the top of the water table; at lower discharge, the top of the water table is closer to the spring outlet. The suspended bacteria wash out in greater numbers with high discharge.
4. When isopods and carbon were added in a pairwise experimental design to sediments collected from the aquifer, the isopods significantly stimulated numbers and activity of planktonic and sedimentary bacteria, while carbon had no effect. This suggests that invertebrates can affect the microbes locally in an aquifer.     

Probing Diversity in the Plankton: Using Patterns in Tintinnids (Planktonic Marine Ciliates) to Identify Mechanisms

In diversity research, the use of survey data appears to have declined in favour of experimental or modeling approaches because direct relationships are difficult to demonstrate. Here we show that use of field data can yield information concerning the mechanisms governing diversity. First, we establish that tintinnids display a global latitudinal pattern of diversity similar to other pelagic organisms; species numbers appear to peak between 20° and 30° north or south. This common large scale spatial trend has been attributed to the gradient in water column structure across the global ocean. We then examine the generality of a relationship between planktonic diversity and water column structure by considering data from the Mediterranean Sea, in which water column structure changes seasonally. Among populations of foraminifera, tintinnids, and the dinoflagellates of the genus Ceratium, we compare data from trans-Mediterranean sampling conducted at different times and monthly changes in species richness at single sites. We find that water column structure alone appears to be a poor predictor of temporal changes in diversity. Lastly, we present an example of temporal changes in tintinnid diversity based on data from an oceanographic sampling station in the N. W. Mediterranean where resources, as chlorophyll, appear distinctly unrelated to changes in water column structure. We show that short-tem temporal changes in diversity (week to week shifts) can be related to changes in chlorophyll concentration. We conclude that in tintinnids diversity can be directly linked to characteristics of food resources.     

Lipid and DNA Evidence of Dominance of Planktonic Archaea Preserved in Sediments of the South China Sea: Insight for Application of the TEX86 Proxy in an Unstable Marine Sediment Environment

The marine planktonic archaea are dominated by Thaumarchaeotal Marine Group I, which is characterized by the lipid biomarker thaumarchaeol. The marine benthic archaea are characterized by greater diversity of currently unknown species whose lipid biomarker signatures are uncertain. In this study, a sediment core from the northwestern part of the South China Sea (SCS) (water depth 1474 m) was analyzed using molecular DNA and lipid biomarker approaches. While 16S rRNA gene analysis showed changing archaeal community structures with sediment depth, this change had little impact on the fossil record of archaeal lipids that are characteristic of the planktonic community. As a result, the fossil archaeal lipids recorded paleo sea surface temperature of the SCS since the last glacial maxima by the TEX₈₆ proxy, which agreed generally with the winter temperature recorded by planktonic foraminiferas collected from the same area of the SCS that hosted mass-transported deposits. This suggests that this deep water deposit may have partially preserved paleoclimate record reflecting seasonal temperature variation in a near shore setting, which is in contrast to annual sea surface temperature or sub sea surface temperature variation recorded by TEX₈₆ in the open ocean.     

Population interaction: A synchronizer for the persistent rhythmicity of Chaoborus larvae

Fifty chaoborid larvae (Diptera: Chaoboridae) were maintained singly in 200-ml. experimental chambers with lake water and sediments. The larvae, entrained in a reversed light-dark cycle-L D 12: 12 (21–09), were monitored at two-hour intervals to observe whether or not the larvae were in the planktonic state. Results indicated that under constant conditions individual larvae varied in the time of movement out of the sediments and subsequent time spent in the planktonic state. A significant difference was observed when the individual activity patterns (i.e. the number of times an individual was observed to be planktonic during the 12-hour observations period) were summated and compared with the population data previously published by LaRow (1968). However, when larvae whose individual activity patterns were recorded, were pooled in a single experimental chamber the activity pattern then observed was identical to that previously reported. It was concluded, that the persistent, diurnal rhythm observed in Chaoborus is most likely a population rhythm and the interaction of the individuals within the population aids in the synchronization of the rhythm.The observation of larvae maintained singly in experimental chambers also enabled one to determine the actual percentage of the benthic population that leave the sediments and become planktonic each night. During the summer months at least 82.8 percent of the fourth instar larvae leave the sediments and enter the water column.     

Planktonic bloom-forming Cyanobacteria and the eutrophication of lakes and rivers

SUMMARY. 1. Eutrophication of water bodies involves the enrichment of plant nutrients, often followed by significant shifts in the phytoplankton towards Cyanobacteria. When comparing different aquatic systems, even with similar nutrient contents and in the same climatic region, inverse deductions are not valid; i.e. (a) the presence of Cyanobacteria does not necessarily indicate eutrophic conditions, or (b) eutrophic or even poly-trophic conditions do not necessarily support cyanobacterial development.
2. Above a threshold of 10 μg 1⁻¹ total phosphorus, the development of Cyanobacteria can be described by physical factors, such as water column stability. By characterizing different forms of turbulence, the presence or absence of Cyanobacteria in lakes and rivers can be predicted.
3.When the turbulence of the water column is rather low, as it is in sheltered or meromictic lakes, Cyanobacteria can build up dense populations. In nutrient poor systems, species of Oscillatoria and (seldom) Aphanizomenon are dominating.
4.If the turbulence of the water column is high (mixing depth much greater than euphotic depth) or the mixing pattern is irregular, as in slowly flowing or regulated rivers, Cyanobacteria are outcompeted.
5. In the presence of frequent or permanent turbulence, but with mixing depths lower or not much greater than the euphotic zone (as it is the case in shallow, unstratified lakes, mostly eutrophic or even hypertrophic), Cyanobacteria can outgrow normally dominant r -strategists under conditions of low N:P ratios, high water temperatures, pH >9.0 or low light availabilities.
6. If turbulence is comparatively great (10 to $15 m) and stable for a longer period of time, some cyanobacteria are able to adapt.
7. Our statements are discussed on the basis of physiological characteristics.     

Geographical patterns of genetic structure in marine species with contrasting life histories

Aim  Phylogeographical breaks may reflect historical or present-day impediments to gene flow, and the congruence of these breaks across multiple species lends insight into evolutionary history and connectivity among populations. In marine systems, examining the concordance of phylogeographical breaks is challenging due to the varied sampling scales in population genetics studies and the diverse life histories of marine organisms. A quantitative approach that considers the effects of sampling scale and species life history is needed.
Location  The south-east and south-west coasts of the United States.
Methods  We quantitatively analysed previously published datasets of marine fauna to look for concordance among phylogeographical breaks. We used a bootstrap approach to determine the regions where phylogeographical breaks are more common than expected by chance among species with planktonic dispersal as well as those with restricted dispersal.
Results  On the south-west coast, breaks were clustered near Point Conception among planktonic dispersers and near Los Angeles among restricted dispersers. On the south-east coast, breaks were most common near the southern tip of Florida for planktonic dispersers and near Cape Canaveral for restricted dispersers.
Main conclusions  Dispersal ability is an important determinant of phylogeographical patterns in marine species. Breaks among planktonic dispersers on both coasts are congruent with present-day flow-mediated barriers to dispersal, suggesting that phylogeographical structure in species with planktonic larvae may reflect contemporary oceanography, while breaks in restricted dispersers reflect historical processes. These results highlight the importance of explicitly considering sampling scale and life history when evaluating phylogeographical patterns.     

Omnivory does not prevent trophic cascades in pelagic food webs

1. Strong trophic cascades have been well documented in pelagic food webs of temperate lakes. In contrast, the limited available evidence suggests that strong cascades are less typical in tropical lakes.
2. To measure the effects of omnivorous tilapia on planktonic communities and water transparency of a small man-made tropical lake, we performed a 5-week in situ enclosure experiment with five densities of fish randomly allocated to 20 enclosures. Zooplankton and Phytoplankton biomasses as well as water transparency were measured weekly.
3. Results show that omnivorous tilapia significantly decreased the abundance of large Cladocerans, increased the abundance of small algae (greatest axial linear dimension <50  μ m) and decreased water transparency as predicted by trophic cascade theory.
4. Therefore, omnivory was not a sufficient factor to prevent a trophic cascade in this pelagic community, although the cascade effect was weaker than reported from many north temperate, nutrient-rich lakes.     

DNA-based analysis of planktonic methanotrophs in a stratified lake

1. The assemblage of planktonic methanotrophs in a stratified freshwater lake was investigated. Vertical patterns were analysed by denaturing gradient gel electrophoresis, using the primer pair specific for 16S rRNA genes of type I methanotrophs.
2. The resulting banding patterns could be divided into three distinct groups, and sequenced bands were all related to the Methylobacter species. No amplicon was obtained with the primer pair specific for type II methanotrophs.
3. Cloning analysis of the pmoA gene was performed using samples from three water depths (epilimnion, metalimnion and hypolimnion). The compositions of the clone libraries from the three depths were distinct from each other but all three libraries were dominated by clones related to Methylobacter species.     

Cellulose production by planktonic algae in lacustrine environments

Cellulose production by planktonic algae in a eutrophic pond and in an oligotrophic lake was estimated by comparing the amount of cellulose contained in intact algal cells with the amount of cellulose present in the water column. Cellulose contents of laboratory grown algal species representing the dominant cellulose producers were ranged from 2 to 39% of the total dry weight of cell mass, depending upon the species and stage of growth. The relative amounts of cellulose present in the water column ranged from 4 to 50% of the total dry weight of particulate matter.It was estimated that more than 30% of cellulose in the water column was actually contributed by the viable algal cells present during the algal bloom. Despite its algal origin, more cellulose was found in the water column than could be accounted for by the number of algal cells observed. The difference was due to the accumulation of cellulose from previous algal crops. This observation indicated that production of algal cellulose exceeded decomposition and little or no decomposition of cellulosic material took place in the water column.     

Predicting the spatial dominance of phytoplankton in a light limited and incompletely mixed eutrophic water column using the PROTECH model

1. A phytoplankton community model [Phytoplankton RespOnses To Environmental CHange (PROTECH)] was used to examine the effect of a wide range of varied light intensities and mixed depths upon simulated phytoplankton populations. Two different column lengths of the simulated water body were examined (the upper 5 m and the whole 14.5 m water column) for each scenario.
2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast-growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.
3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella , Ceratium or Rhodomonas ), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella . This bloom was missed by the 5-m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.
4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model-based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist.