Copepod grazing in a summer cyanobacteria bloom in the Gulf of Finland

Blooms of the cyanobacteria Nodularia spumigena and Aphanizomenon flos-aquae dominated the phytoplankton assemblages of the western Gulf of Finland and the eastern side of the northern Baltic Sea in late July–August, 1992. The bloom overlapped the peak seasonal contributions of the dominant mesozooplankton herbivores in the region, the copepods Acartia bifilosa and Eurytemora affinis and the cladoceran Bosmina longispina maritima. Using radio-labelling techniques; the copepods were offered one of the cyanobacteria, Nodularia, as well as the 10–54 µm fraction of the natural phytoplankton assemblage. In general, incorporation rates of the labelled phytoplankton into the copepods declined with increasing contributions of the cyanobacteria. For both copepods, incorporation was inversely related to total phytoplankton biomass, whether measured as chlorophyll, total cells or cyanobacteria biomass. The very low rates for Acartia (< 0.8 µl [copepod h]^–1) indicated that this copepod was likely starving in the cyanobacteria bloom, consistent with the generally poor condition of the animal observed in the laboratory. The other major mesozooplanktor, B. longispina maritima, ingested substantially more cyanobacterial biomass than the two copepods, based on HPLC-identified cyanobacteria-specific pigment echinenone in the gut. Bloom carbon provided < 1% and < 4% of the daily rations for Acartia and Eurytemora, respectively. Total copepod demand in the cyanobacteria blooms was trivial, < 1% of bloom biomass consumed daily. These results suggest that copepod herbivory is relatively unimportant in dissipating summer cyanobacteria blooms in the Gulf of Finland.     

Periphyton as a potential phosphorus sink in the Everglades Nutrient Removal Project

Phosphorus uptake and release by periphyton mats were quantified in the Everglades Nutrient Removal Project (ENRP) to evaluate the potential for periphyton P removal. Short-term P uptake rates were determined by incubating cyanobacteria (Oscillatoria princeps and Shizothrix calcicola) and Chlorophycean (primarily Rhizoclonium spp.) algal mat samples for 0.5–2 h under ambient conditions in BOD bottles spiked with soluble reactive P (SRP). Cyanobacterial mats removed P more than twice as fast (80–164 μg P h⁻¹ g⁻¹ AFDM) as Chlorophycean mats (33–61 μg P h⁻¹ g⁻¹ AFDM) during these incubations. In a longer term study, fiberglass cylinders were used to enclose 1.8 m² plots within the wetland and were dosed weekly for 7 weeks with: (1) no nutrients; (2) SRP (0.25 g P m⁻² week⁻¹); or (3) SRP plus nitrate (0.42 g N m⁻² week⁻¹) and ammonium (0.83 g N m⁻² week⁻¹). Phosphorus uptake rates by this periphyton assemblage, which was dominated by the chlorophytes Stigeoclonium spp. and Oedogonium spp., were measured weekly and were similar among nutrient treatments on most dates, indicating that the algal storage compartment for P was not saturated despite repeated P additions. Decomposition rates and P loss by cyanobacteria and Chlorophycean mats were determined by measuring biomass loss and SRP release in darkened BOD bottles over 28–42 day periods under anaerobic and aerobic conditions. First-order aerobic and anaerobic decomposition rates for cyanobacterial mats (k = 0.1095 and 0.1408 day⁻¹, respectively) were 4–20-fold higher than rates for Chlorophycean mats (k = 0.0066 and 0.0250 day⁻¹, respectively) and cyanobacteria released considerably more P back to the water column. Our findings suggest that periphyton can be an important short-term sink for P in treatment wetlands and that retention is strongly affected by the taxonomic composition of the periphyton assemblage.     

Water quality improvement and phytoplankton response in the drinking water source in Meiliang Bay of Lake Taihu, China

Water quality experienced changes throughout the 3-year ecological engineering experiment in the drinking water source in Meiliang Bay of Lake Taihu. Average concentrations of TN, TP, NH₄⁺, BOD₅ and transparency in the drinking water source during the period of July–December 2005 were 1.85, 0.13, 0.23, 3.03 mg L⁻¹ and 27.5 cm, respectively, decreasing by 47.9%, 21.2%, 83.3%, 54.4% and 24.2%, compared to concentrations from the same period in 2003. Concentrations of chlorophyll a and COD were 89.9 μg L⁻¹ and 6.45 mg L⁻¹, increasing by 27.9% and 17.7%, compared to the values in 2003. Cyanobacteria (mainly Microcystis) dominated the phytoplankton community in the ecological engineering area during July–December 2005. Densities of cyanobacteria and Microcystis were higher in 2005 than in 2004 and higher inside the engineering area than outside. Density percentages of cyanobacteria and Microcystis to total algae were above 90% and 60% during the bloom period. Average density of flagellate algae was higher during July–December 2005 than in 2004. Changes in water quality in the engineering area resulted mainly from the weakening of waves, decrease in concentrations of suspended solids, and assimilation of mass algae and periphytons. In spite of initial improvement of water quality, cyanobacterial bloom still determined the phytoplankton dynamics and variations. Additionally, nutrient concentration still remained at a high level without control of external loading. Therefore, a more holistic approach and long-term management should be adopted in Lake Taihu.     

Occurrence and toxicity of an Anabaena bloom in a tropical reservoir (Southeast Brazil)

Potentially toxic cyanobacterial blooms are becoming common in the Brazilian reservoirs in all regions of the country. During October 2004, a dense bloom of cyanobacteria occurred in the Monjolinho Reservoir (São Carlos, São Paulo State, Brazil) and a significant amount of cyanobacterial material accumulated on the water surface. Phytoplankton analysis showed that the main species in this bloom were Anabaena circinalis and Anabaena spiroides. Cladoceran (Ceriodaphnia dubia and Ceriodaphnia silvestrii) and mouse bioassays were performed to detect toxic products in extracts of the natural samples collected at the three different dates during in short period. To prepare the extracts, freeze-dried cells were dispersed in distilled water and subjected to repeated freeze/thaw cycles and sonication and centrifuging processes. Crude extracts were toxic both to cladocerans (LC₅₀ 94–406 mg freeze-dried cells L⁻¹) and mice (indicative LD₅₀ 297–445 mg freeze-dried cells kg⁻¹) and the toxicity of the bloom increased for cladocerans during the occurrence of the bloom. Toxin analysis by ELISA revealed that microcystin (MC) was found in the water of the reservoir (concentrations ranging from 28 to 45 μg L⁻¹). In addition, microcystin was also found in freeze-dried cyanobacteria cells with concentrations ranging from 138 to 223 μg g⁻¹. On the other hand, neurotoxins (saxitoxin and gonyautoxin) were not detected in any of the natural samples by HPLC. Signs of toxicity in mice did not indicate whether the bloom samples were predominantly hepatotoxic or neurotoxic. It is known that natural Anabaena blooms can contain other toxic compounds besides microcystins and neurotoxins such as lipopolysaccharides or other toxins not identified or known. Methods of detecting cyanotoxins used in this study were insufficient to clarify the toxicological features of Anabaena bloom and indicated that other methods should be investigated.     

Effects of zooplankton on nutrient availability and seston C : N : P stoichiometry in inshore waters of Lake Biwa, Japan

Forty-eight-hour experimental manipulations of zooplankton biomass were performed to examine the potential effects of zooplankton on nutrient availability and phytoplankton biomass (as measured by seston concentration) and C : N : P stoichiometry in eutrophic nearshore waters of Lake Biwa, Japan. Increasing zooplankton, both mixed-species communities and Daphnia alone, consistently reduced seston concentration, indicating that nearshore phytoplankton were generally edible. The zooplankton clearance rates of inshore phytoplankton were similar to rates measured previously for offshore phytoplankton. Increased zooplankton biomass led to increased concentrations of nutrients (NH₄-N, soluble reactive phosphorus [SRP]). Net release rates were higher than those found in previous measurements made offshore, reflecting the nutrient-rich nature of inshore seston. Zooplankton nutrient recycling consistently decreased TIN : SRP ratios (TIN = NH₄ + NO₃ + NO₂). This effect probably resulted from the low N : P ratios of nearshore seston, which were lower than those commonly found in crustacean zooplankton and thus resulted in low retention efficiency of P (relative to N) by the zooplankton. Thus, zooplankton grazing inshore may ameliorate algal blooms due to direct consumption but tends to create nutrient supply conditions with low N : P, potentially favoring cyanobacteria. In comparison with previous findings for offshore, it appears that potential zooplankton effects on phytoplankton and nutrient dynamics differ qualitatively in inshore and offshore regions of Lake Biwa. Received: September 4, 2000 / Accepted: January 23, 2001     

A survey of toxicity of cyanobacterial blooms in Lake Ladoga and adjacent water bodies

Twentyfive cyanobacterial blooms in Lake Ladoga and adjacent water bodies were studied in the summer of 1990–1992. Toxicity of the water bloom material for mice was detected in 9 cases. The maximal tolerable doses (MTD) of the material extracted from biomass varied within 3–30 mg kg^–1 mouse body weight; 50% lethal doses (LD₅₀) were within 45–125 mg kg^–1. Toxic water blooms were registered in Karelian lakes and in the Neva Bay, Gulf of Finland. Cyanobacterial samples collected on the eastern coast of Lake Ladoga proved to be non-toxic. The species identified in toxic bloom material included Anabaena circinalis, A. flos-aquae, A. lemmermannii, Anabaena sp., Aphanizomenonflos-aquae, Gloeotrichia echinulata, G. pisum, Microcystis aeruginosa and Oscillatoria sp. These data suggest that toxic forms of cyanobacteria are widespread in Karelian lakes belonging to the drainage basin of Lake Ladoga.     

Nutrient fluxes from upwelling and enhanced turbulence at the top of the pycnocline in Mono Lake, California

Time series measurements of temperature at 15 depths and profiles of temperature-gradient microstructure were obtained during a period with strong wind forcing and subsequent calm in Mono Lake, California. The wind forcing increased the amplitude of basin-scale internal waves and energy at all wave frequencies relative to the calm period. Rates of dissipation of turbulent kinetic energy, , were high ( > 10^–6 m² s^–3) at the top of the pycnocline at both an inshore and an offshore site on a day when winds reached 10 m s^–1 and on the following two days at an inshore site ( > 10^–7 m² s^–3). The enhanced turbulence occurred at the depth of a subsurface temperature maximum (z _TM) and coincidentally with elevated concentrations of NH₄, reduced concentrations of chlorophyll a and particulate carbon, and increased abundance of the macrozooplankter Artemia monica. The NH₄ at z _TM was more dispersed and of lower concentration inshore than offshore and indicated greater turbulent transport inshore. Over the course of 4 days, chlorophyll a concentrations increased in the upper mixed layer, and C:N and C:Chl ratios decreased. Offshore, the change in C:N ratio indicated a relaxation of moderate nutrient deficiency. We hypothesize that excretion by A. monica and turbulent transport of the NH₄ from the subsurface temperature maximum led to improved physiological status of phytoplankton in the upper mixed layer.     

Community development and modes of phosphorus utilization in a late summer ecosystem in the central Gulf of Finland, the Baltic Sea

The development of a filamentous, nitrogen-fixing cyanobacterial bloom was followed during July–August 1990 in a stratified basin in the central Gulf of Finland, Baltic Sea. Hydrography, dissolved inorganic, particulate and total nutrients, chlorophyll a, alkaline phosphatase activity, ³²PO₄-uptake and phytoplankton species were measured. The study period was characterized by wind-induced mixing events, followed by marked nutrient pulses and plankton community responses. Phosphate uptake was highest throughout the study period in the size fraction dominated by bacteria and picocyanobacteria (< 2 µm) and the proportion of uptake in the size fraction 2–10 µm remained low (2–6%). Higher phosphate turnover times were observed in a community showing signs of enhanced heterotrophic activity. The bloom of filamentous, nitrogen-fixing cyanobacteria Aphanizomenon flos-aquae was promoted by a nutrient pulse with an inorganic nutrient ratio (DIN:DIP) of 15. The results show that the quality, frequency and magnitude of the physically forced nutrient pulses have an important role in determining the relative share of the different modes of phosphorus utilization and hence in determining the cyanobacterial bloom intensity and species composition in the Baltic Sea.     

Cyanobacteria and cyanobacterial toxins in the alkaline crater lakes Sonachi and Simbi, Kenya

The phytoplankton communities and the production of cyanobacterial toxins were investigated in two alkaline Kenyan crater lakes, Lake Sonachi and Lake Simbi. Lake Sonachi was mainly dominated by the cyanobacterium Arthrospira fusiformis, Lake Simbi by A. fusiformis and Anabaenopsis abijatae. The phytoplankton biomasses measured were high, reaching up to 3159 mg l⁻¹ in L. Sonachi and up to 348 mg l⁻¹ in L. Simbi. Using HPLC techniques, one structural variant of the hepatotoxin microcystin (microcystin-RR) was found in L. Sonachi and four variants (microcystin-LR, -RR, -LA and -YR) were identified in L. Simbi. The neurotoxin anatoxin-a was found in both lakes. To our knowledge this is the first evidence of cyanobacterial toxins in L. Sonachi and L. Simbi. Total microcystin concentrations varied from 1.6 to 12.0 μg microcystin-LR equivalents g⁻¹ DW in L. Sonachi and from 19.7 to 39.0 μg microcystin-LR equivalents g⁻¹ DW in L. Simbi. Anatoxin-a concentrations ranged from 0.5 to 2.0 μg g⁻¹ DW in L. Sonachi and from 0 to 1.4 μg g⁻¹ DW in L. Simbi. In a monocyanobacterial strain of A. fusiformis, isolated from L. Sonachi, microcystin-YR and anatoxin-a were produced. The concentrations found were 2.2 μg microcystin g⁻¹ DW and 0.3 μg anatoxin-a g⁻¹ DW. This is the first study showing A. fusiformis as producer of microcystins and anatoxin-a. Since A. fusiformis occurs in mass developments in both lakes, a health risk for wildlife can be expected.     

Microcystins Induce Morphological and Physiological Changes in Selected Representative Phytoplanktons

Dissolved microcystins (MCs) are regularly present in water dominated by microcystin-producing, bloom-forming cyanobacteria. In vitro experiments with environmentally feasible concentrations (5 × 10⁻⁷ M) of the three most common microcystins, MC-LR, MC-RR, and MC-YR, revealed that they influence the metabolism of different representative phytoplanktons. At light intensities that are close to the cyanobacterial bloom environment (50 μmol m⁻² s⁻¹), they produce morphological and physiological changes in both microcystin-producing and -nonproducing Microcystis aeruginosa strains and also have similar effects on the green alga Scenedesmus quadricauda that is frequently present in cyanobacterial blooms. All three microcystin variants tested induce cell aggregation, increase in cell volume, and overproduction of photosynthetic pigments. All three effects appear to be related to each other but are not necessarily caused by the same mechanism. The biological activity of microcystins toward the light-harvesting complex of photobionts can be interpreted as a signal announcing the worsening of light conditions due to the massive proliferation of cyanobacteria. Although the function of microcystins is still unknown, it is evident that they have numerous effects on phytoplankton in nature. These effects depend on the individual organism as well as on the various intracellular and extracellular signaling pathways. The fact that dissolved microcystins also influence the physiology of microcystin-producing cyanobacteria leads us to the conclusion that the role of microcystins in the producing cells differs from the role in the water environment.     

Microcystins Induce Morphological and Physiological Changes in Selected Representative Phytoplanktons

Dissolved microcystins (MC) are regularly present in water dominated by microcystin-producing, bloom-forming cyanobacteria. In vitro experiments with environmentally feasible concentrations (5 × 10⁻⁷ M) of the three most common microcystins, MC-LR, -RR, and -YR, revealed that they influence the metabolism of different representative phytoplanktons. At light intensities close to the cyanobacterial bloom environment (50 μmol m⁻² s⁻¹), they produce morphological and physiological changes in both microcystin-producing and nonproducing Microcystis aeruginosa strains, and also have similar effects on the green alga Scenedesmus quadricauda that is frequently present in cyanobacterial blooms. All three microcystin variants tested induce cell aggregation, increase in cell volume, and overproduction of photosynthetic pigments. All three effects appear to be related to each other, but are not necessarily caused by the same mechanism. The biological activity of microcystins toward the light-harvesting complex of photobionts can be interpreted as a signal announcing the worsening of light conditions due to the massive proliferation of cyanobacteria. Although the function of microcystins is still unknown, it is evident that they have numerous effects on phytoplankton organisms in nature. These effects depend on the individual organism as well as on the various intracellular and extracellular signaling pathways. The fact that dissolved microcystins also influence the physiology of microcystin-producing cyanobacteria leads us to the conclusion that the role of microcystins in the producing cells differs from their role in the water environment.     

Development of genetic markers in cyanobacteria and stability of genetically marked strains in soil

Reporter marker GUS (-glucuronidase gene from Escherichia coli) and luc operon from the American firefly were introduced into cyanobacteria and the stability of these markers in soil was examined. To transfer the integrational vector into cyanobacteria, the genomic DNA library of Synechocystis sp. or Anabaena cylindrica maintained in pBR 322, pCY 100 and pCY 101 were transformed with HB 101 containing pRL 528 and selected for Cm^r and Amp^r. These clones of HB 101 containing pRL 528 and the vectors carrying different cyanobacterial chromosomal DNA fragments were used for triparental mating with HB 101 [pRK 2013/pRK 2073] and cyanobacteria. The frequency of transconjugants for integrational vectors was between 2.1 × 10^–5 and 4.0 × 10^–4. The transfer frequency of RSF 1010 based vectors (pDSK 519 and pCY 106) was 1.0–4.5 × 10^–4 in Synechocystis sp. whereas A. cylindrica failed to maintain these vectors. Low frequency transfer (2.0–2.3 × 10^–6) of RK 2 based vectors pVK 100 and pCY 104 was observed in A. cylindrica but these were unable to replicate in Synechocystis sp. The vectors in general were stable at least by 74.9% for 60 days of incubation in BG-11 medium. The markers were less stable in A. cylindrica (74.9–84.2%) compared to Synechocystis sp. (80.1–88.8%) at 60 days of incubation. Integrational vectors were almost 85% stable in both the strains. The RK 2 derivative of pCY 104 was less stable in A. cylindrica (74.9–77.3%) than the RSF 1010-based vector pCY 106 in Synechocystis sp. (80.1–81.0%). A maximum of 64.7% of the markers were lost in soil. The chromosomal markers through integrational vectors were found to be highly stable and 68.2–72.7% of these markers were retained in cyanobacteria at 60 days of incubation. Plasmid markers were less stable, with a loss of 64.7–48.7% at the end of the experiment. In A. cylindrica 58–65% of the RK 2 vector was lost whereas in Synechocystis sp. 49–61% of RSF 1010 was lost at 60 days of incubation.     

Biological degradation of algae and microcystins by microbial enrichment on artificial media

The removal efficiency of algae and microcystins (MCs) of a pilot setup based on biological degradation of enrichment microbes by artificial media was studied. The results showed that when chlorophyll-a in Lake Taihu was 3.76–266.1 μg L⁻¹, 62.8% of chlorophyll-a could be removed within a hydraulic retention time of 6–7 days. High-performance liquid chromatography (HPLC) analysis for the detection of MCs was applied. When total microcystins RR and LR (TMC-RR and TMC-LR) and extracellular microcystins RR and LR (EMC-RR and EMC-LR) were 0.23–8.93, 0.14–4.73, 0.12–1.15, 0.02–0.17 μg L⁻¹, respectively, and in source water, the average removal efficiencies of TMC-RR, TMC-LR, EMC-RR, EMC-LR were 67.0%, 40.5%, 40.0% and 66.0%, respectively. The polymerase chain reaction (PCR) electrophoresis chart revealed that there was a large amount of algae-lysing bacteria such as Pseudomonas spp. and Bacillus spp. on the artificial medium. The protozoa number in the assembled medium was higher than in lake water. Enrichment microbes on the artificial medium could effectively degrade algae and microcystins in Lake Taihu.     

Numerical models for management of <Emphasis Type="BoldItalic">Anabaena circinalis</Emphasis>

The control of nuisance species of cyanobacteria in reservoirs is a critical issue for the international water industry, as these organisms can produce toxins and compounds that taint potable water with unpleasant tastes and odours. To assist with effective management of cyanobacterial growth, numerical models that are either site specific or universally applicable can be employed. An artificially destratified reservoir was modelled with the coupled hydrodynamic-ecological numerical model DYRESM-CAEDYM. The validation site was Myponga Reservoir, South Australia, a highly managed drinking water supply reservoir. Chemical dosing (CuSO₄) and artificial mixing via an aerator and two raft-mounted mechanical surface mixers (hereafter referred to as surface mixers) are used at Myponga to manage the growth of the scum-forming cyanobacterium Anabaena circinalis. The dominant phytoplankton community was adequately modelled, and combinations of the various management options were simulated whereupon informed operational strategies could be implemented. Without any intervention, permanent stratification would occur and the growth of Anabaena circinalis would peak above 3 μ g L⁻¹, producing geosmin that would exceed the taste and odour threshold (10 ng L⁻¹); with the individual use of the aerator or surface mixers, growth of Anabaena circinalis was significantly reduced to below 1 μ g L⁻¹.     

Relative Uptake of Urea and Ammonium by Dinoflagellates or Cyanobacteria in Shrimp Mesocosms

The relative role of the organic nitrogen source, urea, versus ammonium as a nitrogen source for two species of dinoflagellates was compared with one species of cyanobacteria. Experiments were conducted opportunistically in nutrient-rich marine water during blooms of 34either cyanobacteria or dinoflagellates in outdoor mesocosms. These replicate mesocosms, which were stocked with shrimp fed high-protein formulated feeds, contained high biomasses of phytoplankton (mean chlorophyll a concentrations, 439.2–811.2 μg l⁻¹). ¹⁵N-urea and ammonium uptake rates for dinoflagellate-dominated blooms (Gymnodinium pulchellum-complex (Larsen), Karlodinium micrum (Larsen) (Dinophyceae)) were compared with blooms of the cyanobacterium, Romeria sp. (Cyanophyceae) in mesocosms with mean urea and ammonium concentrations ranging from 2.32 to 3.24 μM, and 7.39 to 64.85 μM, respectively. Urea uptake rates were significantly (p < 0.005) lower than ammonium uptake rates irrespective of which algal species dominated the bloom. Additionally urea uptake rates were not significantly higher in G. pulchellum-complex or K. micrum-dominated blooms than in Romeria sp. blooms. These results suggest that G pulchellum complex and K. micrum may not be gaining a competitive advantage in waters high in dissolved organic matter simply by preferentially utilizing urea. The periodic dominance of these species in highly organic environments, such as shrimp ponds, is likely to have a more complex explanation.     

Grazing and assimilation rates of natural populations of planktonic rotifersKeratella cochlearis,Keratella quadrata andKellicottia longispina in a eutrophic lake (Aydat,France)

The filtering rates of¹⁴C labelledChlamydomonas sp. by 3 dominant species of rotifers were studied in eutrophic Lake Aydat. They varied from 4 to 53 µl ind^–1 h^–1 forKeratella cochlearis, from 2 to 56 µl.^–1h^–1 forKeratella quadrata and from 3 to 52 µl ind^–1 h^–1 forKellicottia longispina. Their maximum assimilation efficiency was 32%. At the measured grazing rates, these populations could clear the water in less than two days during July. In Lake Aydat, the rotifers community could play an important role in the regulation of seasonal succession of phytoplankton and bacteria.     

Incidence of microcystin‐producing cyanobacteria in Lake Tana,the largest waterbody in Ethiopia

The occurrence of toxic cyanobacterial blooms is a serious problem for fast‐developing countries in Africa, such as Ethiopia, that are struggling with significant degradation of the natural environment and limited access to water of good quality. Research undertaken on Lake Tana in Ethiopia between 2009 and 2011 was intended to assess the seasonal threat from cyanobacteria and to select methods for tracking of this threat in the future. The cyanobacterial genus Microcystis was found to be present throughout the monitoring period, and M. aeruginosa was determined as the dominant species. Moreover, in all samples, toxigenic cyanobacteria with the potential to produce microcystins were detected. High levels of microcystins, ranging from 0.58 to 2.65 μg L^?1, were detected each November, which indicates that in the postrainy season, water usage should be limited. The correlation between concentrations of chlorophyll‐a and microcystins suggested that chlorophyll‐a could be used as an indicator of the potential presence of cyanobacterial‐derived hepatotoxins in Lake Tana in the future. Furthermore, for quick quantitative confirmation of the presence of microcystins, a simple and rapid ELISA test was recommended.     

Impacts of two biomanipulation fishes stocked in a large pen on the plankton abundance and water quality during a period of phytoplankton seasonal succession

Silver and bighead carp were stocked in a large pen to control the nuisance cyanobacterial blooms in Meiliang Bay of Lake Taihu. Plankton abundance and water quality were investigated about once a week from 9 May to 7 July in 2005. Biomass of both total crustacean zooplankton and cladocerans was significantly suppressed by the predation of pen-cultured fishes. There was a significant negative correlation between the N:P weight ratio and phytoplankton biomass. The size-selective predation by the two carps had no effect on the biomass of green alga Ulothrix sp. It may be attributed to the low fish stocking density (less than 40 g m⁻³) before June. When Microcystis dominated in the water of fish pen, the pen-cultured carps effectively suppressed the biomass of Microcystis, as indicated by the significant decline of chlorophyll a in the >38 μm fractions of the fish pen. Based on the results of our experiment and previous other studies, we conclude that silver and bighead carp are two efficient biomanipulation tools to control cyanobacterial (Microcystis) blooms in the tropical/subtropical eutrophic waters. Moreover, we should maintain an enough stocking density for an effective control of phytoplankton biomass.     

Cation-exchange capacity of algae and cyanobacteria: A parameter of their metal sorption abilities

Summary The potential metal sorption abilities of algae and cyanobacteria were estimated as cation-exchange capacities, using a potentiometric titration method. Unicellular cyanobacteriaAnacystis nidulans, Synechocystis aquatilis, and the green microalgaStichococcus bacillaris revealed a higher maximal capacity (205–825 eq g^–1 dry wt) than filamentous macroalgaVaucheria sp. (Xanthophyceae, 41 eq g^–1 dry wt). The cation-exchange capacity decreased when external pH decreased. Different ion-exchange properties of cell surfaces of cyanobacteria and algae were observed.