Efeitos da cianobactéria tóxica Cylindrospermopsis raciborskii na alimentação, sobrevivência e reprodução de um copépodo calanóide neotropical

Abstract

Cyanobacterial blooms can cause negative impacts on water quality and biological communities. Among these biological communities, calanoid copepods have a great importance, being the dominant planktonic group in many freshwater systems. Despite the importance of calanoid copepods to plankton dynamics in freshwater systems, studies on the interaction between these animals and cyanobacteria are still scarce. Here the effects of the invasive and toxic cyanobacterium Cylindrospermopsis raciborskii (Woloszyńska) Seenayya et Subba Raju (1972) on the tropical calanoid copepod Notodiaptomus iheringi (Wright 1935) were evaluated. Feeding (clearance rates and selective feeding), survival (Kaplan-Meier curves, survival probabilities and hazard ratios) and reproduction (% females with eggs and egg production) of this copepod were studied using single and mixed diets of C. raciborskii and nutritious algae (Chlamydomonas chlorastera or Cryptomonas obovata). The increase on C. raciborskii proportion (> 50%) was related to lower feeding rates although no differences between the clearance rates on the cyanobacterium and nutritious algae within each treatment were found. Negative (25 or 75% of C. raciborskii) or neutral (50% of C. raciborskiii) effects on survival were detected throughout the treatments. On the other hand, the reproduction in N. iheringi was strongly affected by the presence of C. raciborskii, independently of the proportion of this cyanobacterium. Features of the species C. raciborskii such as toxicity (e.g. saxitoxins) and low nutritional values (e.g. absence of PUFA) along with non-previous acclimation in N. iheringi to C. raciborskii might explain the different outcomes found in the present study. Overall, N. iheringi copepods can feed and survive in diets with C. raciborskii. However, C. raciborskii diets cannot support reproduction of these animals. This is the first study that evaluates the effects of C. raciborskii on survival and reproduction of calanoid copepods. The outcomes found in this work might contribute to the understanding of the feeding interactions as well as the population dynamics of calanoid copepods in the presence of the cyanobacterium C. raciborskii.