Frieda B. Taub

UNIQUE INFORMATION CONTRIBUTED BY MULTISPECIES SYSTEMS: EXAMPLES FROM THE STANDARDIZED AQUATIC MICROCOSM

Single-species toxicity tests are inadequate to predict the effects of chemicals in ecological communities although they provide data on the relative toxicity of different chemicals, and on the relative sensitivity of different organisms. Only multispecies studies can provide demonstrations of: (1) indirect trophic-level effects, including increased abundances of species via increased food supply through reduced competition or reduced predation; (2) compensatory shifts within a trophic level; (3) responses to chemicals within the context of seasonal patterns that modify water chemistry and birth and death rates of populations; (4) chemical transformations by some organisms having effects on other organisms; and (5) persistence of parent and transformation products. Multispecies laboratory studies, such as the Standardized Aquatic Microcosm, have much to offer, with advantages of statistical power, speed of analyses, demonstrated reproducibility among laboratories, and modest expense (compared to field stu...

Demonstration of pollution effects in aquatic microcosms

Trophic level interactions caused by an algicide, an insecticide, and two levels of organic enrichment were demonstrated in alga‐grazer‐bacteria microcosms; e.g., the insecticide caused an algal bloom by removing grazers. The technique was expanded to develop an unbiased bioassay of the effects of low levels of HgCl2, CdCl2, Toxaphene, and Aroclor (PCB) 1242. Problems of toxicant recovery, solvent effects, repeatability, and statistical analyses were uncovered. In an algal chemostat, Aroclor 1242 generally prevented the maintenance of steady state densities.

Responses of blue-green and green algae to streptomycin in unialgal and paired culture☆

Abstract Streptomycin sulfate prevented growth of six blue-green algae at concentrations (0.09 to 0.86 mg/l) substantially lower than needed to prevent growth of 7 of 8 green algae tested. Chlorella vulgaris, Scenedesmus obliquus and Ulothrix sp. grew in active streptomycin concentrations less than 21 mg/l, while Chlamydomonas reinhardtii growth was prevented at concentrations of 0.66 mg/l. Algal growth in sublethal concentrations of streptomycin was slowed or delayed, and the maximum density attained by several species was decreased. These data suggest that attempts to select ‘representative’ species for toxicity testing may have mixed success: any blue-green alga would be a suitable representative of Cyanophyta with respect to streptomycin, but no single green alga would adequately represent the wide range of response to streptomycin seen among the Chlorophyta species tested. To test for interactions between competition and chemical inhibition, paired cultures of S. obliquus with Anabaena cylindrica, Ankistrodesmus sp., C. vulgaris and Selenastrum capricornutum were observed with and without 6.6 mg/l streptomycin. The outcome of competition was consistent with predictions based on single-species assays, where major differences in chemical sensitivity were present, although significant interactions were observed. S. obliquus populations when treated with streptomycin were competitively superior to A. cylindrica and S. capricornutum. Significant interactions between competition and streptomycin treatement were also observed for paired cultures of C. vulgaris and S. obliquus; neither population fit the model of additive effects of chemical inhibition and competition.

Designing a microcosm bioassay to detect ecosystem level effects

Predicting the effect of a pollutant in an ecosystem requires knowledge of ecological processes such as competition and predator‐prey interactions. Chemical and toxicological information are not adequate. Multispecies laboratory microcosms are suggested as a tool for demonstrating ecological effects in a biologically and statistically acceptable way. Some examples of microcosms, the statistical properties of the data, and design criteria for better microcosms are presented.

Stepwise iterative calibration of a multi-species phytoplankton-zooplankton simulation model using laboratory data

Abstract A multi-species phytoplankton-zooplankton simulation model was rigorously calibrated using laboratory data. The model is a system of ordinary differential equations describing the dynamics of eight functional groups of phytoplankton, seven groups of zooplankton, and nitrogen and phosphorus forms. Processes represented in the model include nutrient uptake, photosynthesis, respiration, excretion, egestion, mortality, and nutrient recycling. A stepwise iterative calibration procedure was used with data from laboratory experiments involving various combinations of biota mixes and two initial nutrient concentrations. Calibration proceeded in four steps: (1) calibration of five of the eight phytoplankton groups to single and paired species experiments performed under both initial nutrient concentrations, (2) calibration of the remaining phytoplankton groups to single-species growth experiments and to an ‘ungrazed’ experiment (all phytoplankton without zooplankton), and (3 and 4) calibration of the zooplankton and nutrient recycling portions of the model to data from a full microcosm experiment (all phytoplankton and zooplankton together). Two constraints were imposed during calibration: (1) at each step, values of parameters determined during previous steps were not allowed to be varied from their calibrated values, and (2) a single set of parameter values had to be found for each functional group that provided satisfactory fits to all experiments involving that functional group. Based on both graphical comparisons and statistical goodness-of-fit measures, satisfactory model fits to data were obtained. The importance of representing intracellular nutrient pools for phytoplankton and size structure for zooplankton are demonstrated, and the benefits and drawbacks of using data from controlled laboratory and field systems for model development and calibration are discussed.

Copper Dynamics and the Mechanism of Ecosystem Level Recovery in a Standardized Aquatic Microcosm

The Standardized Aquatic Microcosm (SAM) was used to assess the effects and behavior of copper at the ecosystem level. The concentration of algal cells and Daphnia magna, pH, dissolved organic carbon (DOC), and dissolved and ionic copper concentration were measured for 489 d and used to explain the recovery sequence of a community of organisms. The results indicate that a resistant algal species was crucial for initiating the recovery sequence in these microcosms and that the timing of D. magna blooms was variable but highly correlated with decreasing ionic copper. In order to explain copper toxicity and the success of the recovery phase, a stepwise analysis of the functional role of the resistant algal species Oocystis pusilla, and the tolerance of D. magna was undertaken. These process studies determined that O. pusilla was a suitable food for D. magna, and that this algal species could also act as a major ligand for copper, although sorption was probably important only for a limited time during the bloom. These studies also concluded that copper bioavailability controlled toxicity because it was shown that D. magna from the microcosms exhibited no resistance to copper toxicity, even though the dissolved copper concentration was 5 times the LC50 value (concentration lethal to 50% of the population). DOC and pH, which were controlled by algal metabolism, were probably important for decreasing ionic copper, which allowed the recovery sequence to begin. Additional studies showed that the microcosm-derived DOC was able to complex copper at low pH and that DOC was highly correlated with reduced concentrations of ionic copper.

Modeling the effect of algal biomass on multispecies aquatic microcosms response to copper toxicity

Abstract A model was developed to simulate the effects of copper on an aquatic microcosm consisting of 10 phytoplankton species and 5 zooplankton species grown in a defined medium. The copper toxicity equations in the model were based on the results of single species toxicity tests at different initial cell densities. Model output was evaluated by comparing predictions with results of replicated [3] 35 day microcosm experiments having copper added at 3 different times (days 7, 14 or 21) at 500 ppb concentration. These experiments offered a wide range of plankton and nutrient conditions at the time of copper addition. The baseline for these experiments was set by a control experiment, with no copper addition and a model, MICMOD, developed to simulate microcosm behavior. Two toxicity models were tested; the ‘neutral’ model defined copper toxicity to plankton as depending only on the dissolved copper concentration in the medium, while the ‘biomass’ model also decreased toxicity in proportion to algal biomass. Graphical and statistical comparisons showed the toxicity model including algal biomass to better fit the data. Both the experimental results and the model suggest that the effects of copper may be strongly influenced by the density and species composition of the biota and the related differences in water chemistry at the time of copper addition. The apparent importance of algal biomass to copper toxicity may be due to (1) changing copper availability either through direct absorption or adsorption, (2) production of chelates by the algae which complex copper in less toxic forms or (3) changing the pH which affects copper ionization and particularly the concentration of the cupric ion (Cu2+) form, which is highly toxic.

EFFECTS OF HYDROXAMATE SIDEROPHORES (STRONG Fe (III) CHELATORS) ON THE GROWTH OF ALGAE1

Varying concentrations of Fe were tested with three hydroxamate siderophores to demonstrate the interactions affecting growth of Chlamydomonas reinhardtii and Chlorella vulgaris. Schizokinen was purified from the excretions of the blue‐green alga Anabaena sp. grown in low‐Fe medium. Chlamydomonas reinhardtii was inhibited by schizokinen when in molar excess of the Fe concentration; the inhibition was overcome with excess Fe. The growth of C. vulgaris was not affected by this chelator. Results with desferrioxamine were similar. A weaker chelator, rhodorulic acid, did not inhibit the growth of either alga. Low concentrations of the chelators may stimulate algal growth when Fe precipitates are hydrolyzed. Since different algae respond differently to the presence of the chelators, the observed interactions could be important in determining competitive relationships when Fe is limiting. If an alga can excrete a strong chelating agent, as does Anabaena, algae lacking the ability to compete with the chelator may not grow.

Copper tolerance by the freshwater algal species Oocystis pusilla and its ability to alter free-ion copper

Abstract Previous studies with copper-stressed microcosms found that recovery was dependent on a copper-resistant algal species [Taub, 1989. Aquatic Ecotoxicology: Fundamental Concepts and Methodologies, pp. 47–92. Meador, J.P., Taub, F.B., Sibley, T.H., 1993. Ecol. Appl. 3, 139–155]. One algal species, Oocystis pusilla, was able to bloom in microcosms that had been devoid of organismal activity for several weeks due to the addition of copper at a high concentration (31.5 μM). In the present study, experiments were performed to characterize the range in tolerance of O. pusilla to copper, determine its growth under low and high pH regimes as a function of copper exposure, and to examine its ability to alter pH and ionic-copper activity (ICu) over time. Total-copper (TCu) concentrations up to 78.7 μM and ICu values as high as 0.9 μM had no negative effects on O. pusilla, indicating that it is highly copper-tolerant. The best growth for O. pusilla generally occurred in the range of 8–20 μM (total or dissolved copper), indicating a hormetic effect (enhanced response at intermediate concentrations). Even though its abundance was severely depressed in a TCu solution of 157.5 μM, this species was able to increase fourfold in 14 days. O. pusilla increased its numbers at a faster rate in high pH (≈9) solutions; however, it was able to propagate when pH was lower (≈7) and copper was high. These characteristics would allow this species to bloom in highly copper-stressed environments that would characteristically have a low pH. From this work, and related studies, we concluded that the primary mechanism allowing O. pusilla to reduce ionic-copper activity in culture solutions and microcosms was the release of organic copper-complexing ligands and that biomass sorption may have been important only at very high cell densities.

A continuous culture apparatus for the mass production of algae

Abstract A multi-stage, continuous culture apparatus has been designed and tested for the production of algae for larval molluscs and crustacea. A single-line system produced a maximum of 2.4 × 10 11 cells/day, or 5 g ash-free dry weight of Monochrysis lutheri . Multiple-line systems are recommended for hatcheries. The flow rate affected algal cell density, yield, biomass, protein level, and residual nitrate. Maximal cell yield occurred at 10 I flow per day, a dilution rate of 63% of the volume of the first growth carboy, or 30% of the volume of the total system. The system is also adaptable to growth of larger planktonic algae or mixed cultures of algae and protozoa and/or rotifers.