BIOACCUMULATION OF CYANOTOXINS AND THEIR EFFECTS ON AQUATIC ORGANISMS

Abstract

revista vol 13 nº 2.indd

Cyanobacteria are photosynthetic procariotes with wide geographic distribution, occurring in many different ecossystems. They produce secondary metabolites named cyanotoxins, which can be classified in three main types: hepatotoxins, dermatotoxins and neurotoxins. Many studies showed the effects of cynobacteria and their toxins over aquatic organisms, including acute effects (reduction in survivorship, feeding inhibition, paralysis) and chronic effects (e.g. reduction in growth and fecundity). Some studies also reported biochemical alterations, (e.g. on the activity of phosphatases, GST, AChE, and proteases) and behavioral alterations. The main target of these toxins seems to be the herbivorous zooplancton, thus research efforts have foccused on this link as the main bioaccumulators of cyanotoxins, showing indeed its potential for bioaccumulation in the food chain. However, the large variability found in results of many studies has lead to equivocal conclusions. Although there is unequivocal evidence of deleterious effects of cyanobacteria and their toxins, the resistance of some zooplâncton species and the absence of effect of microcystins on Daphnia in some studies raised the question whether this toxin would be serving as a chemical defense mechanism against zooplancton grazing. The present manuscript presents a broad review of studies about bioaccumulation and the effects of cyanotoxins on freshwater organisms.