Natural Plankton Communities Research Articles

Direct measurements of natural planktonic bacterial community viability by flow cytometry

A range of fluorescent viability dyes were used in conjunction with flow cytometry to rapidly enumerate viable bacteria from freshwater environments. Optimal labelling was achieved by using carboxyfluorescein diacetate or chemchrome B with a detergent-mediated permeabilization step. The viable bacterial count under optimal conditions was 7% in oligotrophic lake water and 75% in polluted river water.

Phytoplankton dynamics in the River Meuse as affected by pollution

The temporal and spatial dynamics of phytoplankton in the River Meuse and a number of physical and chemical parameters were analyzed to gain insight into the pollution level in the river affecting the phytoplankton community. During 1993, samples were taken every two months at eight stations along the River Meuse for physical, chemical and biological characterization of the water. In February, water samples were also taken for laboratory incubations of the natural plankton community. The algae showed a rapid successive development with highest densities (up to 77 mg chlorophylla l−1) in the middle reach of the river in spring and summer. During winter algal biomass remained very low. A substantial input of nutrients (nitrogen, phosphorus) was observed in the middle reach of the river. Concurrently, an increase in temperature and a reduction in pH was observed. Furthermore, the toxicity of polar organic compounds in the Microtox test showed a strong increase up to the city of Liege and the Belgian/Dutch border; the water quality improved further downstream. The relatively high toxicity at the location Liege was reflected in relatively low growth rates of phytoplankton in the laboratory experiments using water from these locations.

Ecosystem-Level Effects of Zebra Mussels (Dreissena polymorpha): An Enclosure Experiment in Saginaw Bay, Lake Huron

We examined the short-term effects of zebra mussels (Dreissena polymorpha) on ecosystem processes in late August 1991 in Saginaw Bay, Lake Huron. Four 1,600-L enclosures, made of Fabreen with a diameter of 1 m, a depth of 2 m, and closed at the bottom, were used to enclose natural plankton communities. These communities were dominated by diatoms with some chlorophytes, chrysophytes, and cyanophytes. Phytoplankton growth was limited by P-availability. Two enclosures were held as controls, and zebra mussels encrusting unionid shells were suspended in two of the enclosures: one enclosure (HZ) contained approximately four-fold greater numbers of mussels than the other (LZ). The concentration of suspended particles, chlorophyll, and algal biomass in HZ and LZ declined over a 6-day interval. Diatom numbers declined more than other taxa. Phytoplankton growth rates in HZ and LZ increased to near μmax; there was no apparent change in photosynthetic parameters a or Pmax scaled for chlorophyll. Soluble reactive P (SRP) increased significantly (p < 0.05) in HZ but not LZ. Dissolved organic P (DOP) and ammonium ion were elevated; dissolved organic carbon (DOC) was unchanged in HZ and LZ. The rate of phosphate uptake by bacteria and algae declined to less than 2% of controls; this rate decrease could not be explained simply by grazing losses or isotope dilution. The rate of ammonium regeneration by the plankton and the potential rate of ammonium uptake by the plankton did not differ significantly in HZ or LZfrom the control enclosures. Our findings indicate that the zebra mussel can have significant short-term effects on phytoplankton abundance, water transparency, water chemistry and phosphorus dynamics. We propose a model of zebra mussel effects that suggests high densities of zebra mussels may indirectly alter and control those processes that are rate-limited or concentration-limited by nutrient availability.

Nonequilibrium plankton community structures in an ecohydrodynamic model system

Abstract. Due to the local and global impacts of algae blooms and patchiness on water quality, carbon cycling and climate, models of plankton dynamics are of current interest. In this paper, the temporal and spatial patterns in natural plankton communities are interpreted as transient and stationary nonequilibrium solutions of dynamical nonlinear interaction-diffusion-advection systems. A simple model of phytoplankton-zooplankton dynamics (Scheffer, 1991) is presented in space and time. After summarizing the local properties as multiple stability and oscillations, the emergence of spatial and spatio- temporal patterns is considered, accounting also for diffusion and weak advection. In order to study the emergence and stability of these structures under hydrodynamic forcing, the interaction- diffusion-advection model is coupled to the hydrodynamic equations. It is shown, that the formation of nonequilibrium spatio-temporal density patterns due to the interplay of the deterministic nonlinear biological interactions and physical processes is a rare occurrence in rapidly flowing waters. The two-timing perturbation technique is applied to problems with very rapid single-directed steady flows. A channel under tidal forcing serves as and example for a system with a relatively high detention time of matter. Generally, due to the different time and length scales of planktic interactions, diffusion and transport, initial nonequilibrium plankton patches are simply moved through the system unless the strong hydrodynamic forces do not destroy them before.

Iron and regenerated production: Evidence for biological iron recycling in two marine environments

We investigated biological Fe recycling in plankton communities from two contrasting marine ecosystems, the equatorial Pacific and Monterey Bay, California. Our experiments involved addition of cultured cyanobacteria and diatoms labeled with Fe radiotracer to natural plankton communities. Transfer of label into the natural community was followed by size fractionation and microautoradiography, and intracellular Fe was determined with titanium wash techniques. We documented the transfer of labeled Fe from added cyanobacteria to indigenous large cells in both environments and from large diatoms to indigenous small cells in the equatorial Pacific. Microautoradiography and Ti washing verified that transfer occurred from and into intracellular fractions in Monterey Bay experiments, although substantial amounts of transferred Fe were also found to be surface-adsorbed or associated with detritus. We argue that, as is the case for N, recycling of cellular Fe to support regenerated production could be an important component of marine ecosystem dynamics, especially in areas low in Fe.

Rotifers as predators on small ciliates

Clearance rates of Synchaeta pectinata, Brachionus calyciflorus and Asplanchna girodi on Tetrahymena pyriformis (46 µm in length) at a density of 10 cells ml−1, in the presence of algal food, were 2.5 to 6.1 ml rot.−1 day−1. Clearance rates of these rotifers were, respectively, about 2, 3, and 13 times lower on Strobilidium gyrans (58 µm in length) than on T. pyriformis, indicating that the saltations of S. gyrans are an effective escape response. Clearance rates of S. pectinata were considerably lower on Colpidium striatum (81 µm) than on S. gyrans, suggesting that S. pectinata may not be able to ingest ciliates of this size. S. pectinata had a clearance rate of 19 ml rot.−1 day−1 on S. gyrans at a density of 1.2 cells ml−1, in the absence of edible algal food. Rotifers may prey extensively on ciliates in natural plankton communities, ingesting 25 to 50 individuals in the 45–60 µm size range day−1.

Spatio-temporal pattern formation in nonlinear non-equilibrium plankton dynamics

Because of the local and global impacts of algae blooms and patchiness on water quality, carbon cycling and climate, models of plankton dynamics are of current interest. Here the temporal and spatial patterns in natural plankton communities are interpreted as transient and stationary non-equilibrium solutions of dynamical nonlinear interaction-diffusion-advection systems. The analysis of a simple model of phytoplankton-zooplankton dynamics in space and time is presented. Nutrients and planktivorous fish are not treated separately, but they act as environmental control variables. After summarizing the local properties, the emergence of spatial and spatio-temporal patterns is considered. Conditions for the formation of spatial patterns after the diffusive instability of a uniform species distribution are derived, and numerical results of diffusive as well as shear-diffusive patterning are presented on a two-dimensional spatial cross-section. The variability of phytoplankton growth due to its light sensitivity is considered in a linear approximation. Multiple stability, oscillations, the propagation of planktic fronts as well as stationary and drifting patches are presented.

Susceptibilities of different‐sized ciliates to direct suppression by small and large cladocerans

SUMMARY Laboratory experiments compared the susceptibilities of six ciliates and the rotifer Keratella cochlearis to predation and interference from Daphnia pulex and Bosmina longirostris. Susceptibilities of the ciliates to D. pulex were similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible to B. longirostris as to the much larger D. pulex. The jumping response of the oligotrich Strobilidium gyrans appeared to be an effective defence against B. longirostris. Clearance rates of B. longirostris and D. pulex on different ciliate species at a density of 1,3 ciliates ml−1 ranged from 1–30 to 5–24ml ind.−1 day−1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susceptible species.

Mercury and methylmercury, in individual zooplankton: Implications for bioaccumulation

Using trace-metal-clean sampling and handling techniques along with ultrasensitive analytical procedures, it is possible to measure both total Hg and monomethylmercury (methyl-Hg) in natural planktonic communities with the same level of taxonomic, ontogenic, and trophic resolution that is currently possible in fish communities. In an experimentally manipulated lake, both acidification and trophic position enhanced the bioaccumulation of methyl-Hg in the plankton. A consistant pattern of methyl-Hg enrichment (2−4 ×) in water, bulk phytoplankton, and individual zooplankton was associated with a 1.5 unit pH decrease in Little Rock Lake. Regardless of pH, bioconcentration factors [Bf = log(Cb/Cw), where Cb and Cw are Hg concentrations in biota and water] were substantially higher for methyl-Hg than those for total Hg or nonmethyl-Hg at three pelagic trophic levels (~10−100×). Between each trophic level, the Bf(methyl-Hg) increased by ~0.5 log units, clearly indicating biomagnification. Although somewhat higher in the acidified basin, Bf(methyl-Hg) was more strongly influenced by trophic position than by pH. This suggests that methyl-Hg was bioaccumulated largely in proportion to supply and that acidification may have directly increased supply to the base of the food chain.

Diel changes in dark respiration in a plankton community

The dark respiration of a natural plankton community from an eutrophic lake was studied in a laboratory scale enclosure (LSE), exposed to illumination which simulated natural light conditions in the water column. The dark respiration was measured continuously for 2 hours in samples obtained from the LSE each hour for 26 hours. The relationships between dark respiration rates, carbohydrate concentrations and other parameters were investigated.

Seasonal and daily changes in bacterivory in a coastal plankton community

Fluorescently labeled bacteria (FLB) were used to examine the long-term changes (monthly for 8 mo) and short-term changes (daily for 10 d) of bacterial grazing in a natural plankton community. Two preliminary experiments also were performed to evaluate the effect of sample volume, incubation time, and light regime on the results. Experimental results indicate a 'bottle effect' for the 3 smallest sample volumes employed (100, 200, 500 ml); lower grazing rates were always observed during 24 h incubations than during 48 h incubations. The light regime (continuous darkness, continuous light, 12L:12D) did not affect grazing rates during a 48 h experimental period. Bacterivory in the seasonal study in Vineyard Sound, Massachusetts (USA) was highly responsive to water temperature and was the primary factor determining grazing pressure over the winter-summer period. Samples incubated at 20°C during winter consistently exhibited higher rates of consumption of bacteria than a triplicate set of samples incubated at ambient water temperature or 5°C. Daily fluctuations in the rates of bacterivory during a 10 d period in May were significant, but were ca 1/10 the magnitude of the seasonal fluctuation. Maximal rates of bacterivory removed up to 60 % of the bacterial assemblage daily.

Metal enrichment experiments in the Weddell-Scotia Seas: Effects of iron and manganese on various plankton communities

During the European Polarstern Study (EPOS 1988/1989) in the Weddell and Scotia Seas, five series of metal enrichment experiments were carried out with natural plankton communities under ultraclean conditions. Despite a clear stimulation of growth by the addition of Fe, control bottles (no additions) also showed rapid buildup of Chl a and complete utilization of a major nutrient within 2 weeks, indicating nonlimiting ambient Fe levels. Effects of Mn additions were less pronounced or absent, whereas extra additions of Zn and Cu in one experiment showed little or no effect. The species composition of the plankton community, monitored by HPLC pigment analysis and microscopic observations, changed in favor of diatoms when Fe was added. The addition of Fe also caused an increase in microzooplankton densities and concentrations of pigment breakdown products. However, metal-mediated shifts in the plankton community were minor compared to major changes resulting from incubation. Changes were most pronounced in experiments where microzooplankton was strongly developed, presumably as a result of excluding mesozooplankton from the bottles. Fe had an impact on plankton growth and species composition, but other factors seem to be responsible for keeping phytoplankton productivity far from its potential in these Antarctic waters.

Effect of Anabaena flos‐aquae on the abilities of Daphnia and Keratella to feed and reproduce on unicellular algae

SUMMARY. This study tests the hypothesis that the filamentous cyanobacterium, Anabaena flos‐aquae, inhibits Daphnia's ability to feed and reproduce on unicellular algae more than it does Keratella's. Double‐label radiotracer experiments using whole and sonieally disrupted Anabaena filaments showed that even low concentrations of Anabaena (5 × 103 cells ml−1) inhibited the abilities of Daphnia pulex and D. galeata mendotae to feed on Chlamydomonas and that this inhibition was due to both mechanical interference with feeding and increased food availability. A single‐label radiotracer experiment showed that Anabaena (5 × 103 and 2 × 104 cells ml−l) reduced the abilities of neonate, juvenile, and adult D. pulex to feed on Chlamydomonas but had a much more pronounced effect on adults. Single‐label radiotracer experiments using screened (25 μm mesh) and unscreened suspensions of whole Anabaena filaments showed that only very high concentrations of Anabaena (105 cells ml−1) reduced the ability of Keratella cochlearis to feed on Cryptomonas and that this inhibition probably was due to mechanical interference with feeding, since Keratella ate Anabaena extremely inefficiently ‐ especially when single cells and short filaments were removed by screening. Experiments comparing the survivorship and fecundity of individuals fed Anabaena, Chlamydomonas, or no food showed that the Anabaena was not toxic to either Keratella or D. galeata mendotae, was not utilized by Keratella, and was utilized by Daphnia, although not as well as Chlamydomonas was. Anabaena (5 × 103 or 104 cells ml−1) did not affect, or slightly increased, the population growth rate (rm) of K. cochlearis on Cryptomonas, while it substantially increased that of D. pulex, Duphnia's ability to utilize Anabaena probably more than offset its reduced ability to feed on Cryptomonas. The presence of cyanobacterial filaments in natural plankton communities could adversely affect Daphnia and decrease its ability to competitively suppress Keratella and other rotifers if the filaments were of little nutritional value to the Daphnia, greatly interfered

Rapid ammonium cycling and concentration‐dependent partitioning of ammonium and phosphate: Implications for carbon transfer in planktonic communities

A short‐lived radioactive isotope of nitrogen (13N, half‐life = 10 min) of very high specific activity (&gt;100 mCi µmol−1) was used to study NH4+ uptake at near‐ambient concentrations in natural planktonic communities. The turnover times of the dissolved NH4+ pool in Long Island Sound ranged from tens of hours between April and early June to a fraction of an hour between mid‐June and late July. The NH4+ turnover time was also rapid in a nearby eutrophic lake. Up to 50% of the ambient NH4+ flux into particulate material from Long Island Sound was attributable to organisms passing 1.0‐µm polycarbonate filters. Partitioning of NH4+ uptake among size classes was, however, very concentration‐dependent. A 0.5 µM addition resulted in an increase in NH4+ uptake by the &gt;3‐µm size class of from 33% to &gt;80% of the total. Similar results were obtained for PO43− uptake into particulate matter from the Sargasso Sea. Although &lt;20% of the ambient PO43− uptake was into particles &gt;1 µm, a 100 nM pulse resulted in about 50% of the uptake entering the &gt;1‐µm fraction. Because slight increases in NH4+ and PO43– concentration result in greater uptake by larger organisms with higher C : N and C : P ratios, distributing these nutrients in “patches” of elevated concentration results in more C being transferred to higher level consumers.

The effects of atrazine on microcosms developed from four natural plankton communities

Comparisons were made among Leffler microcosms developed from four different natural communities and exposed to 0, 20, 100, 200, 500, 1,000, and 5,000 micrograms/L atrazine, a commonly used herbicide. Atrazine reduced net primary productivity, pH, and net productivity/respiration ratios in all four microcosm communities. In three of the four communities, the lowest observed (P less than 0.05) effect concentration (LOEL) was 100 micrograms/L. In the fourth community the LOEL was 200 micrograms/L atrazine. The sensitivity and accuracy of bioassays with four different microcosm communities were evaluated by comparing results with values reported for acute and chronic single species bioassays, other types of microcosms, and experimental ponds exposed to similar concentrations of atrazine. The ranges of sensitivity noted in these experiments were less than the range reported for single species bioassays using common test organisms and similar to those reported for other microcosms. The similarity between Leffler microcosm results and the responses reported for the experimental ponds suggests that the Leffler microcosms accurately reflected concentrations causing ecosystem level changes in the experimental ponds.

Effects of fluorene on microcosms developed from four natural communities

AbstractEcosystem‐level responses were examined in microcosms developed from four different natural plankton communities and exposed to nominal concentrations of 0.12, 0.50, 2.0, 5.0 and 10.0 mg/L fluorene, a polynuclear aromatic hydrocarbon. The lowest observed (p &lt; 0.05) effect level (LOEL) for dark respiration (Rni) was 0.12 mg/L fluorene in three of the four communities during the first 14 d. The LOEL for Rni in the fourth community was 5.0 mg/L. The LOEL of the net productivity/respiration ratio (Pn/Rni) was 0.12 mg/L in all four communities. These results suggest that the responses of these microcosms were not completely independent of their source communities. The sensitivities or LOEL values from these microcosm experiments were as low as those reported for chronic bioassays of the three most sensitive of seven standard test organisms. Comparisons between the responses of these microcosms and those reported for experimental ponds exposed to the same concentrations of fluorene suggest that these microcosms accurately reflect the types of changes and concentrations that cause change in pond ecosystems. However, slight but significant changes in the ecosystem‐level variables gave no indication of the almost complete elimination of some zooplankton populations at 5.0 and 10.0 mg/L in the ponds and at 2.0, 5.0 and 10.0 mg/L in the microcosms. This lack of correspondence between population‐ and ecosystem‐level measurements suggests that test measurements made at one hierarchical level of organization may not always be appropriate for estimating effects at other levels.

Fluorescence properties of the freshwater phytoplankton: Three algal classes compared

The fluorescence properties of exponentially growing freshwater diatoms, green and blue-green algae were compared with a standard filter fluorometer and a scanning spectrofluorometer. Green algae and diatoms excited with blue light had R values (ratio of in vivo fluorescence to extractable chlorophyll a) up to 50 times higher than the cyanophytes. There were also considerable differences in R between species within each algal class—coefficients of variation were typically 35–50%—and this variation was slightly increased by treatment with the non-cyclic electron flow inhibitor, 3(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU). A major component of blue-green algal fluorescence was the red light emission from phycobilin accessory pigments. This contribution characterized their emission and excitation spectra and suggested a rapid assay for cyanophyte dominance, which was tested on natural plankton communities. Phycobilin fluorescence was insensitive to DCMU and resulted in highly wave-length-specified variations in CFC (cellular fluorescence capacity, the rise in fluorescence upon addition of DCMU). CFC values for blue-greens were consequently low when measured in the broad bandpass fluorometer, but were up to three times higher when measured with the spectrofluorometer set to the emission peak for photosystem II chlorophyll a. Similar results were obtained with natural populations of blue-green algae. The phycobilin content of blue-green species was influenced by nitrogen source and light quality during growth, and this resulted in variable R and CFC values. Fluorescence properties of diatoms and green algae were less responsive to environmental conditions during growth. Both diatoms and green algae exposed to bright light for 15 min demonstrated a strong reduction in R. Conversely blue-green algal fluorescence was depressed very little, or more commonly, was slightly enhanced by bright light. These observations underscore the importance of species composition and choice of fluorometer as critical determinants of measured algal fluorescence properties.

Development of marine periphyton under mercury stress in a controlled ecosystem experiment

Our laboratory is engaged in studies on the ecotoxicology of chemicals and tries to bridge the gap between laboratory and field conditions by conducting experiments with natural Dutch coastal plankton communities enclosed in large plastic bags, in which the influence of pollutants is investigated. In the experiment reported here, in which mercury was added to the bags, substrates of glass and polyethylene were exposed in the water and the development of the biomass and the species composition of the periphyton was measured.

Large-Scale Enclosed Water-Column Ecosystems an Overview of Foodweb I, the Final CEPEX Experiment

Enclosures of various sizes and configurations have been employed to maintain natural planktonic communities and to examine their responses to pollutants (e.g. Menzel &amp; Steele, 1978; Steele, 1979). Studies on feeding, growth, and mortality of larval fishes, at times conducted in conjunction with pollution experiments, have also been successfully conducted in large enclosures (Koeller &amp; Parsons, 1977). Implicit in these and other comparable studies has been the expectation (or hope) that a balance could be achieved between the advantages and difficulties inherent in more traditional field and laboratory studies. Field studies offer the realism of working with the natural assemblage with its many interacting components and links, but also suffer the disadvantage associated with a turbulent and advective system, which generally makes the repetitive sampling of the same populations impossible. Laboratory studies reverse the balance; control and definition of the components are gained at the expense of realism. The use of large containers represents a hybrid approach characterized by a partial control over a moderately realistic ecosystem. In the ideal case, the use of large containers allows sufficient control to permit experimental manipulation of (and the testing of hypotheses concerning) planktonic assemblages which are sufficiently realistic to permit extension of the experimental results to the ‘real world’.

Uptake of glycine by natural phytoplankton communities

Uptake of [14C]glycine by various size fractions of natural plankton communities was measured to determine if phytoplankton can compete effectively with other members of the plankton community for the free amino acids in seawater. The simultaneous occurrence of glycine uptake, plant pigments, and photosynthetic activity in the same size fractions, as well as autoradiography of the plankton samples, indicated that in some cases phytoplankton were responsible for 50% or more of glycine uptake. Comparison of prefiltration and postfiltration procedures for this type of study provided an explanation for the discrepancy between these results and those of previous studies.