Space use and feeding patterns of an offshore fish assemblage in a shallow mesotrophic lake

Synopsis Diel and spring/summer space-use and feeding patterns were investigated in an assemblage dominated by five fish species occupying the offshore waters of Lake Opinicon, a shallow mesotrophic lake in southeastern Ontario. We assessed fish distribution and diel movement in May and July through the use of gill nets set at various depths in 1.5–7.0 m depth contour zones, supplemented by observations of fish reaction to the nets. Golden shiners and alewives occupied the upper part of the water column, with the former concentrated at the littoral zone-open water interface, and the latter in the open water. Yellow perch occupied the lower part of the water column in all depth contours. Bluegills were abundant in the upper to midwater depths in all contour zones; black crappies were concentrated in the 2.5–3.5 m zones. All of these species showed either a diel or a spring-summer change in distribution pattern. Bluegills were more abundant in offshore locations in July, whereas golden shiners and yellow perch were more abundant onshore in May. Alewives and black crappies showed distinct diel movements in July, as they were largely absent from the study area during the day, but returned at night to feed. In general, there was more spatial separation among the five species in July than in May.Patterns of spatial distribution among the species generally corresponded with the type and variety of prey consumed, and with diel movement of prey in the case of water column feeders. Other factors that apparently affected spatial distribution and seasonal shifts in this assemblage were risk of predation (golden shiner), spawning activity (alewife), and a decline in prey abundance from spring to summer (bluegill and yellow perch).     

Small-scale vertical distribution of phytoplankton, nutrients and sulphide below the oxycline of a mesotrophic lake

A characteristic vertical sequence of phytoplankton populationswas observed below the metalimnetic oxycline of a stratified,mesotrophic lake. Ceratium spp., Closterium acutum and Aphanizomenonflos- aquae were present in the epilimnion but had distinctpopulation maxima in the microaerobic chemocline. Below thesepopulations, Cryptomonas phaseolus, Planktothrix clathrata,Pseudanabaena catenata and Limnothrix sp. followed each otherin the transition zone between the chemocline and the sulphide-containinghypolimnion. The dominating populations of P. clathrata andP. catenata caused a deep chlorophyll maximum. Phytoplanktonstructure was determined by the vertical gradients of sulphideand light. Compared with the epilimnion, nutrient availabilitywas not fundamentally better below the oxycline but the algaemight have benefited from reduced grazing pressure in theirhabitat.     

Fungal infections of the phytoplankton: seasonality, minimal host density, and specificity in a mesotrophic lake

Phytoplankton infections by fungal parasites in the upper, mixed layer of a mesotrophic northern temperate lake were analysed according to the following parameters: host and parasite species, host population density and prevalence of infection, resting spore formation by the parasite, and the lowest host density at which parasites appeared. The phytoplankton taxa recorded included the Cyanobacteria, Dinomastigota, Chrysophyceae, Bacillariophyceae, Chlorophyceae, Cryptophyceae and Haptophyceae, but infection was never found in the last two classes. The parasites belonged almost exclusively to the monocentric Chytridiomycetes. Fungal epidemics occurred at all times of the year. Parasites appeared at population densities as low as about 1 cell ml⁻¹ in some host species, with infection prevalence sometimes exceeding 80%. The proportion of the total phytoplankton biovolume infected by fungi was usually much <1%, but occasionally reached 10%. Parasitism proved to be highly species-specific, with one parasite species usually infecting only one host species. In the case of Zygorhizidium planktonicum , which infected both Asterionella formosa and Synedra acus , there is evidence that two species-specific formae speciales , each infecting only one of these two host species, are present in the lake.     

Community structure of planktonic rotifers in a mesotrophic lake

Seasonal changes of species diversity (H_r) and average spatial overlap (ō_jk) of planktonic rotifers in a mesotrophic lake were examined with respect to their dependence on habitat diversity (H_h) and on a predator (Asplanchna herricki). H_r was positively correlated with the density of A. herricki and with H_h. In the absence of A. herricki there was no correlation between H_r and H_h. ō_jk was negatively correlated with the density of A. herricki and with H_h; the correlation between ō_jk and H_h was independent of the presence of the predator.     

Characterization of phytoplankton extracellular products (PDOC) and their subsequent uptake by heterotrophic organisms in a mesotrophic forest lake

The magnitude of phytoplankton release of photosyntheticallyproduced dissolved organic carbon (PDOC), the size distributionand chemical nature of the released substances, and the quantityand composition of PDOC that were immediately assimilated byheterotrophic bacteria were investigated in a meso- to oligotrophic,mesohumic forest lake by means of the ¹⁴CO₂ technique. The percentageextracellular release (PER) was comparatively high (up to {smalltilde}40%). The bulk of the released substances was of highmol. wt (>5000 dalton), with a minor contribution from lowmol. wt (<1000 dalton) compounds. Heterotrophic bacteriapreferentially assimilated the high molecular weight componentsof PDOC, and a polysaccharide of {small tilde}6000 dalton witha very short turnover time was a key substance in the carbonflow from autotrophic phytoplankton to heterotrophic bacteria.The shortcomings of the ¹⁴CO₂ method to assess phytoplanktonrelease of PDOC is critically evaluated and discussed.     

Correlation between algal species diversity index and phytoplankton community biomass in a mesotrophic lake (West Siberia, Russia)

The study deals with phytoplankton biodiversity in mesotrophic Sartlan Lake, a large natural saline water body in the south of West Siberia. Two different approaches are used: floristic and ecological cenotic. The former is good for determining and analyzing the phytoplankton species composition. The latter gives a quantitative estimation of the phytoplankton biodiversity from the equation of information theory: $ H_b = - \sum\limits_{i = 1}^n {\frac{{B_i }} {B}\log _2 \frac{{B_i }} {B}} The study deals with phytoplankton biodiversity in mesotrophic Sartlan Lake, a large natural saline water body in the south of West Siberia. Two different approaches are used: floristic and ecological cenotic. The former is good for determining and analyzing the phytoplankton species composition. The latter gives a quantitative estimation of the phytoplankton biodiversity from the equation of information theory: , where H _b is the biodiversity (bits); B _i is the population biomass of the species i; B is the entire phytoplankton community biomass (mg/l). A reliable stable negative correlation exists between the phytoplankton biomass and species diversity. Analytical equations and a diagram are given to illustrate the correlation between these values. Original Russian Text ? V.I. Ermolaev, 2009, published in Sibirskii Ekologicheskii Zhurnal, 2009, Vol. 16, No. 4, pp. 623–628.     

Growth limitation of planktonic bacteria in a large mesotrophic lake

We studied nutrient-limitation of bacterioplankton growth in Lake Constance, a mesotrophic lake, between February and August in 1992. We amended 1-m filtrates with a single nutrient or nutrient combinations at 5 or 10 m final concentration, and the limiting nutrient or nutrient combination was inferred from the assay in which bacterial growth was most stimulated. The following nutrients were added individually or in combination: glucose, amino acids, peptone, and ammonium as C and N sources, and inorganic phosphate. From January until the beginning of the phytoplankton spring bloom in mid-April, C alone was growth-limiting. During the spring bloom a complex growth-limitation pattern occurred; first P was limiting, then for only 1 week C + N together, and thereafter P + C. During the clear-water phase with very low chlorophyll concentrations, P + C together limited bacterial growth again, interrupted by a period when C + N + P shortage caused a triple limitation. Later in the season, P + C were growth-limiting again. The growth efficiency (bacterial biomass produced/substrates used) on the basis of amino acid and carbohydrate used varied between 17 and 35%. The addition of various C and N sources indicated that the growth efficiency strongly depended on the quality of the substrates and the adaptation of the bacterial assemblages, for example, whether C and N originated from amino acids or glucose and ammonium.     

Seasonal changes of C:P ratios of seston, bacteria, phytoplankton and zooplankton in a deep, mesotrophic lake

• 1 The C:P ratios of seston, bacteria, phytoplankton and zooplankton were measured twice a week in situ in mesotrophic, large and deep Lake Constance from April to December 1995. Except for zooplankton, a strong seasonality was exhibited with low C:P ratios during P‐enriched early spring conditions and high values during P‐depleted summer conditions.
• 2 Molar C:P ratios of seston varied between 180:1 and 460:1 demonstrating moderate phosphorus limitation in spring and during the clear‐water phase, and strong limitation for the rest of the season. The sestonic C:P ratio increased significantly during two decades of re‐oligotrophication of Lake Constance, reflecting an enhanced phosphorus limitation of the plankton community in summer. Molar C:P ratios of bacteria and phytoplankton varied seasonally between 50:1 and 130:1 and 180:1 and 500:1, respectively, and indicate carbon or light limitation in winter and phosphorus limitation in summer. Zooplankton had a molar C:P ratio of about 124:115 which was nearly constant throughout the seasons.
• 3 These differences in the C:P ratios of planktonic organisms have direct implications for phosphorus recycling within the food web as C:P ratios of excreta should be highly variable.

     

Intra-annual variation of phytoplankton community responses to factorial N,P, and CO2 enrichment in a temperate mesotrophic lake

1. Across primary producer communities in different lakes, nitrogen (N) and phosphorus (P) can exhibit many different patterns of limitation. Here, we look at the intra-annual variability of these patterns in a single lake. Furthermore, we investigate whether a third resource, carbon dioxide (CO₂) can have significant effects on phytoplankton biomass and community composition.
2. We performed five in situ lacustrine mesocosm experiments at different times of the year. In each experiment, we had a factorial design with two levels of N, P and CO₂ enrichment (no enrichment or double lake concentrations for N and P and atmospheric (400 ppm) and c. 1,000 ppm for CO₂) resulting in a total of eight treatments. Mesocosms of c. 1,600 L were suspended in a temperate, mesotrophic lake (Lac Hertel, Canada). Each experiment lasted 2 weeks and chlorophyll a biomass, coarse chemotaxonomic community composition (measured using fluorometry), and several environmental variables were recorded at a minimum of four time points.
3. We found that the limiting, synergistic, and community composition effects of N and P varied between experiments. TN:TP ratios explained, in part, some of this variability, along with insolation and water temperature.
4. Despite relatively high levels of CO₂ in the control mesocosms, we found a constant synergistic effect of CO₂ with N. In combination with the synergistic effect of P with N found in some experiments, this provides support for CO₂ as one of the multiple limiting resources in nutrient-enriched systems. This finding could have implications for eutrophic lakes exposed to increasing concentrations of CO₂.
5. We also found that the effects of CO₂ on community composition varied intra-annually. Thus, we conclude that generalised predictions about the effect of CO₂ on community composition at a coarse chemotaxonomic scale are unlikely to hold, but predictions specific to season and system are likely to be reliable.

     

Use of dissolved carbohydrates by planktonic bacteria in a mesotrophic lake

Dissolved carbohydrates comprise one of the largest pools of labile organic matter readily available for bacterial use in pelagic ecosystems. Despite this fact, very little is known about use of dissolved carbohydrates by planktonic bacteria. We studied use of total dissolved carbohydrates (TDCHO) by planktonic bacteria in mesotrophic Lake Constance, Germany, from April until August 1992. We examined the decrease of TDCHO over time together with the increase of bacterial numbers in 1-m filtered lake water incubated at in situ temperature in the dark. TDCHO analyses were done after hydrolysis by sulfuric acid as free monosaccharides and oxidation by periodate to formaldehyde with 3-methyl-2-benzothiazolinone-hydrazon-hypochloride (MBTH). Preliminary tests showed that hydrolysis by sulfuric acid gave higher yields than hydrolysis by HCl. Our results show that TDCHO are readily used by bacteria and compose substantial fractions of the C requirements for their growth. Concentrations of TDCHO varied between 1.7 and 5.5 m (glucose equivalents), and use rates varied between 0.47 and 3.43 g C liter^–1 h^–1. Highest rates of TDCHO use occurred during the phytoplankton spring bloom, during the clear-water phase in June, and during a phytoplankton bloom in August. Ratios of use of TDCHO/bacterial biomass production varied between 0.17 and 3.05. During the spring bloom, TDCHO and total dissolved amino acids (TDAA) were used in equal amounts. During the clear-water phase at chlorophyll a concentrations <3 g liter^–1, however, bacteria only consumed TDCHO and excreted amino acids. The growth efficiency based on the consumption of TDCHO and TDAA varied between 16 and 21% during the phytoplankton spring bloom and was 35% during the clear-water phase. Correspondence to: M. Simon     

Bacterial growth and losses due to bacterivory in a mesotrophic lake

Bacterial secondary production and rates of bacterivory weredetermined from samples collected from mesotrophic Lake Arlington.Bacterial production and losses were determined by comparingthe growth of natural bacterial assemblages in the presenceof predators (unfiltered samples) to growth in the absence ofpredators (water filtered through 1.0 (im porosity filters).Growth rates of heterotrophic nanoflagellates (HNF) were estimatedfrom growth in the absence of predators (water filtered through5.0 µm porojity filters). Bacterial growth rates rangedbetween 0.002 and 0.069 h^–1 and averaged 0.026 h^–1.HNF grew at rates ranging between 0.003 and 0.107 h^–1and averaged 0.028 h^– Grazing rates ranged between 0.002and 0.043 h^–1, and averaged 0.018 h. The annual averagerate of bacterial biomass synthesis was 3.2 –g Cl^–h^–1 and {small tilde}69% of this production was grazed.Temporal changes in growth and grazing rates suggest a tightlycoupled predator-prey linkage in this lake. ¹Present address: Hydrobiological Institute, Czech Academy ofSciences, Na sddkach 7, 370 05 teski Budjovice, Czech Republic     

Analysis of the shape of P vs I curves of a natural phytoplankton assemblage during the year in the mesotrophic Lake Maarsseveen (I), The Netherlands

Production versus light response curves were made of natural phytoplankton assemblages during the year in an incubator at 8 different light intensities ranging from 60 to 1500 Einstein.m^–2.sec^–1. The shape of these curves is analyzed in relation to the sensitivity for photo-inhibition. At the end of the month of April, there is a sudden shift in this sensitivity at higher light intensities. The algal assemblage becomes less sensitive for photo-inhibition. The influence of light-adaptation, temperature, nutrient limitation and species composition is discussed.     

Top-down effects of crustacean zooplankton on pelagic microorganisms in a mesotrophic lake

A series of single-factor in situ experiments was conductedin a mesotrophic lake in Brandenburg, North Germany, to studythe predatory impact of Eudiaptomus graciloides (adults, copepodites,nauplii), cyclopoid copepods (adult Diacyclops bicuspidatus,Thermocyclops oithonoides) and daphnids (adult Daphnia hyalina,Daphnia cucullata) on the microbial community (bacteria, autotrophicpicoplankton, flagellates, ciliates). All zooplankton speciestested reduced the ciliate community significantly and ingestionrates were always higher for ciliates in the 20–55 µmsize category as compared to smaller ciliates (10–20 µm).Adult E.graciloides, which exhibited the highest predatory impacton ciliates, differed from cyclopoids and daphnids by theirability to decimate ciliates to very low abundances. Ingestionrates of ciliates by the crustacean zooplankton followed thesequence E.graciloides > daphnids = cyclopoids = copepodites.While top-down control was evident for ciliates, top-down effectsdown to the autotrophic picoplankton and flagellates were mostlyrestricted to Daphnia-dominated treatments. Top-down effectswere never strong enough to produce negative bacterial growthrates. For all zooplankton tested, clearance rates for ciliatesexceeded those for phytoplankton. Besides the potential of thecrustacean zooplankton to influence the structure of ciliatecommunities, ciliates may contribute to the energy demands ofcopepods and daphnids, especially when phytoplankton resourcesare limited.     

Dimethylsulfoniopropionate turnover is linked to the composition and dynamics of the bacterioplankton assemblage during a microcosm phytoplankton bloom

Processing of the phytoplankton-derived organic sulfur compound dimethylsulfoniopropionate (DMSP) by bacteria was studied in seawater microcosms in the coastal Gulf of Mexico (Alabama). Modest phytoplankton blooms (peak chlorophyll a [Chl a] concentrations of approximately 2.5 microg liter(-1)) were induced in nutrient-enriched microcosms, while phytoplankton biomass remained low in unamended controls (Chl a concentrations of approximately 0.34 microg liter(-1)). Particulate DMSP concentrations reached 96 nM in the enriched microcosms but remained approximately 14 nM in the controls. Bacterial biomass production increased in parallel with the increase in particulate DMSP, and nutrient limitation bioassays in the initial water showed that enrichment with DMSP or glucose caused a similar stimulation of bacterial growth. Concomitantly, increased bacterial consumption rate constants of dissolved DMSP (up to 20 day(-1)) and dimethylsulfide (DMS) (up to 6.5 day(-1)) were observed. Nevertheless, higher DMSP S assimilation efficiencies and higher contribution of DMSP to bacterial S demand were found in the controls compared to the enriched microcosms. This indicated that marine bacterioplankton may rely more on DMSP as a source of S under oligotrophic conditions than under the senescence phase of phytoplankton blooms. Phylogenetic analysis of the bacterial assemblages in all microcosms showed that the DMSP-rich algal bloom favored the occurrence of various Roseobacter members, flavobacteria (Bacteroidetes phylum), and oligotrophic marine Gammaproteobacteria. Our observations suggest that the composition of the bacterial assemblage and the relative contribution of DMSP to the overall dissolved organic sulfur/organic matter pool control how efficiently bacteria assimilate DMSP S and thereby potentially divert it from DMS production.     

Nitrogen and phosphorus recycling in Lake Sammamish,a temperate mesotrophic lake

This paper presents nitrogen and phosphorus budgets for spring and summer for the trophogenic (0–9 m) and tropholytic (9–27 m) zones of Lake Sammamish. The objective of constructing the budgets is to evaluate the efficiency of nutrient recycling and increase knowledge of the overall nutrient dynamics.The budgets reveal that uptake and solubilization are the dominant fluxes and that nutrient recycling is generally efficient, with the possible exception of early spring during the diatom bloom. This leads to greater reductions in the dissolved N and P pools in spring than summer. Sedimentation is greater in spring because of a pulse immediately following the diatom bloom.Solubilization of particulates is much less in the tropholytic zone than the trophogenic zone. This is due to slower decomposition rates there and to the efficiency of solubilization in the overlying trophogenic zone which results in a relatively small particulate influx. Turnover times for the N and P pools are therefore much faster in the trophogenic zone than in the tropholytic zone. In the trophogenic zone, however, the dissolved N pool turns over much more slowly than the dissolved P pool because of its larger size relative to algal growth requirements.Overall there is a net loss of N and P from the water column in spring primarily due to sedimentation and denitrification whilst in summer there is a small net gain because of sediment release and a slight excess of inflow over outflow.The work was supported by National Science Foundation grants DEB 74-20744, BMS 74-20744 and GB 36810F to the International Biological Program, Western Coniferous Biome (US/IBP) and grant R 008512 from the US Environmental Protection Agency. Contribution no. 373 by the Western Coniferous Biome.The work was supported by National Science Foundation grants DEB 74-20744, BMS 74-20744 and GB 36810F to the International Biological Program, Western Coniferous Biome (US/IBP) and grant R 008512 from the US Environmental Protection Agency. Contribution no. 373 by the Western Coniferous Biome.     

Water level as the mediator between climate change and phytoplankton composition in a large shallow temperate lake

Hydrobiologia - We studied the effect of water level changes in Lake Võrtsjärv (270 km2, mean depth 2.8 m) on the abundance and composition of phytoplankton based on a 35-year database....     

Modelling the effects of changing retention time on abundance and composition of phytoplankton species in a small lake

1. The phytoplankton community model, PROTECH, was used to model the algal response to changing annual mean retention time in a small lake. 2. Simulations of short retention time with a fixed nutrient load resulted in a reduced chlorophyll concentration. A similar relationship was observed when the simulations were repeated but with inflowing nutrients increased in proportion to river discharge. 3. Longer retention time caused the spring bloom to start earlier and the autumn bloom to persist longer. 4. Changes in discharge of the inflowing river also caused a change in the thermal structure of the lake. This change in thermal structure, in turn, influenced the magnitude and composition of the phytoplankton population, particularly those in the CS‐functional group, such as Aphanizomenon.     

Environmental variability drives phytoplankton assemblage persistence in a subtropical reservoir

Temporal changes of assemblages may result from environmental variability and reflect seasonal dynamics of their ecosystem. In the subtropics, the hydrological regime is usually characterized by well‐defined wet and dry seasons, regulating discharge and influencing a series of environmental variables that affect phytoplankton persistence. Therefore, we may expect that dry seasons are environmentally more stable than wet seasons. We analysed interannual phytoplankton assemblage variability (or, inversely, persistence) in a subtropical reservoir sampled every austral summer and winter during 5 years. We tested (i) if phytoplankton assemblage structure differed between the dry (summer) and wet (winter) seasons; (ii) if assemblage persistence differed between the seasons; (iii) if assemblage persistence was related to environmental stability; and (iv) if assemblage dissimilarity increased over time. Phytoplankton assemblages differed between the summer and winter seasons. Winter indicator species were mostly Bacillariophyceae or Cryptophyceae, whereas Cyanophyceae and Chlorophyceae taxa were more frequent and abundant in summer. Assemblages in the dry season were more persistent among years than those occurring during rainy periods. Similarly, environmental variability tended to be lower among dry than among rainy seasons. The relation between the phytoplankton temporal cycle and the temporal patterns of environmental variability supports our prediction that high environmental stability results in more persistent assemblages. Assemblage dissimilarity increased as sampling years were farther apart, for both seasons. Additionally, assemblages in the rainy periods showed a more pronounced increase in dissimilarity, as their changes among years were less predictable. We found a clear temporal pattern and an increased dissimilarity over time in the phytoplankton assemblage structure. Unravelling these temporal patterns may improve our understanding of phytoplankton temporal dynamics, and may have implications for management and monitoring programs. High dissimilarity of assemblages among years, particularly among rainy periods, can obscure human impacts, and monitoring programs should take this into account.     

Yeast diversity in a mesotrophic lake on the karstic plateau of Lagoa Santa,MG-Brazil

The yeast diversity in a paleo-karstic lake of the Lagoa Santa plateau was studied during March 1986–March 1987. Water samples were collected monthly at five stations and the yeasts were isolated at 25 °C on Sabourad dextrose agar supplemented with 0.5% of yeast extract and 10 mg% of chloramphenicol. August and February showed the highest numbers of isolates, coinciding, respectively with the beginning and the ending of stratification. Of 56 isolated species, Aureobasidium pullulans, Candida famata, Cryptococcus albidus, Cryptococcus laurentii, Rhodotorula glutinis, Rhodotorula rubra and Trichosporon cutaneum occurred at the highest frequencies. A. pullulans showed greatest prevalence during the dry period (winter), whereas C. famata, Cr. albidus, Cr. laurentii and Rh. rubra were prevalent during the rainy season (summer). Tr. cutaneum was distributed between July and November. Most isolates yeasts are associated with plants and soils, and are important in decomposition of aquatic macrophytes. Furthermore, a possible role of these species as indicators of pollution is discussed.