Toxic effects of Pseudanabaena tenuis (Cyanobacteria) on the cladocerans Daphnia magna and Ceriodaphnia dubia

Resumo

Some cyanobacteria can produce toxins that affect the aquatic biota and represent a human health risk. The cyanobacterium Pseudanabaena tenuis was isolated from the Valle de Bravo dam, and cultured in the laboratory under controlled conditions. We determined the acute toxic effects and performed a chronic (consumption) test in the cladocerans Daphnia magna (a reference test organism) and Ceriodaphnia dubia (a cosmopolitan species). To determine acute toxicity, three exposure ways were assayed: a) cell-free culture medium, b) crude cell extracts of the cyanobacterium after lysing, and c) aqueous extracts of P. tenuis phycobiliproteins. On the other hand, both cladocerans were fed P. tenuis, assessing the effects on survival and reproduction. For comparison, a control culture of both cladocerans was fed the green microalga Pseudokirchneriella subcapitata. Exposure to the cell-free culture medium did not produce any mortality in either cladoceran, but the aqueous and crude extracts generated acute toxicity. D. magna and C. dubia were negatively affected when fed P. tenuis, since their survival, total progeny, average number of neonates per clutch, and the number of clutches decreased. C. dubia was more sensitive than D. magna, both in the acute toxicity tests and to the effects of P. tenuis consumption. Although most of the blooms around the world are dominated by cyanobacteria of the genus Microcystis, attention should be given to other species, such as P. tenuis, because, frequently, it is not recognized that smaller cyanobacteria could exceed the larger species in terms of biomass, and produce noxious biological effects