During a cyanobacterial bloom in a eutrophic environment, particularly at the end when decomposition occurs, toxic compounds such as the cyanotoxins and the lipopolysaccharides can be released in high concentrations into the water column damaging aquatic organisms. In this work, the effects of this release of toxic compounds during a cyanobacterial bloom were investigated. The acute and chronic toxicity of cyanobacterial crude extracts from two natural blooms in the Barra Bonita and Ibitinga reservoirs (Middle Tietê River, São Paulo State, Brazil) and of a toxic strain cultured in the laboratory were tested. The cladocerans Daphnia similis, Ceriodaphnia dubia and Ceriodaphnia silvestrii were used as test organisms. In the chronic toxicity tests, only a native cladoceran found in Brazilian freshwaters, Ceriodaphnia silvestrii, was used. Microcystins were detected in all cyanobacterial samples. The acute toxicity tests showed that the crude bloom material extract from the Ibitinga Reservoir (48-h EC(50) values between 32.6 and 35.8 microg microcystin g(-1) of freeze-dried material) exhibited higher toxicity to cladoceran than did the crude bloom material extract from Barra Bonita Reservoir (48-h EC(50) values between 46.0 and 80.2 microg microcystin g(-1) of freeze-dried material). The chronic toxicity test data showed that the three extracts reduced the fecundity of C. silvestrii, and the crude extract of Barra Bonita Reservoir bloom material also affected the survival of this cladoceran. Both acute and chronic tests effectively prognosticated possible changes in the cladoceran population, and probably other components of the biota due to cyanobacterial blooms in natural aquatic ecosystems.

Aim In the present study has analyzed several aspects of the life history traits of Melanoides tuberculata, an exotic species, under laboratory conditions, and its response to some stressors has also been applied. Methods Sensitivity to two toxic substances was tested. The mollusks were collected and cultured in the laboratory under controlled conditions of temperature of 25 ± 1 °C and ad libitum food regime. Growth rates and biomass were experimentally obtained and the individual growth curve obtained. Results The experiment lasted 287 days and the maximum shell lengths registered was 11.67 mm. The growth curve indicated a rate of 3.98 year-1 and a maximum theoretical length of 10.61 mm. The mean post-embrionary development time until first reproduction was 275 days and the size of the primipara was 10.13 mm. An accelerated growth of juveniles was observed with fast increase in the shell length until sexual maturity, but growth rate decreased afterwards as more energy was devoted to reproduction. Under the combination of 25 °C and fed on alternate days, M. tuberculata had a slow growth and a long-life expectancy under laboratory conditions. The tolerance of this mollusk to temperature as a stressor ranged between 16 °C and 37 °C, being the optimum temperature situated between 29 °C and 34 °C. The LC(I)50-24h for reference substances were: 0.70 g L-1 for KCl and 9.05 g L-1 for NaCl. Conclusion Based on these results, we can conclude that M. tuberculata is a species tolerant to temperature and salinity, what partially explains to accordance to its wide and rapid dispersion throughout tropical waters.

Ao CNPq pela concessão da bolsa de mestrado. À Renata, que muito me ensinou e com quem foi maravilhoso ter convivido num clima de amizade e cooperação. À amiga e colega de tantas provações e dificuldades que tornou essa fase mais fácil e muito mais divertida. Obrigada, Fer. À Emanuela e Mariana pelo auxílio no laboratório e pelos momentos de descontração. À Edna e Malu pela boa vontade e carinho com que sempre agiram, quando solicitadas.

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