Can small-bodiedDaphniacontrolRaphidiopsis raciborskiiin eutrophic tropical lakes? A mesocosm experiment

摘要

Raphidiopsis raciborskiiis being considered an expanding, invasive species all over the world. It is a potentially toxin producer cyanobacterium and form blooms specially in (sub)tropical lakes, causing concern to public health. Thus, controlling such phenomena are of vital importance. To test the hypothesis that a tropical clone ofDaphnia laevisis able to reduce the biomass ofR. raciborskii, we performed a mesocosm experiment simulating a bloom of this cyanobacterium in field conditions and exposing it to ecologically relevant densities of daphniids. In addition, we tested the hypothesis that omnivorous fish would be able to exert a top-down effect onDaphnia, decreasing the effectiveness of this control. We used treatments with (10 and 20DaphniaL(-1)) or withoutDaphniaand fish (3 per mesocosm).Daphniawas able to significantly reduce the biomass ofR. raciborskiionly at the highest density tested. Fish had low effect onDaphniabiomass, but it is suggested that nutrient recycling by fish might have contributed to the higherR. raciborskiibiomass in fish treatments. This is the first evidence ofDaphniacontrol over saxitoxin-producing cyanobacteria in a tropical ecosystem.