Effect of temperature on the response of planktonic rotifers to a toxic cyanobacterium

Laboratory experiments show that temperature can play an important role in modifying the effect of toxic cyanobacteria on freshwater, planktonic herbivores. A reproductive-rate assay assessed the effect of temperature on the response of Brachionus calyciflorus and Asplanchna girodi to Anabaena flos-aquae and its endotoxin, anatoxin-a. Using a bootstrap technique, reproductive rates (lambda, from r(m)) in experimental and control treatments were determined from complete life tables, and responses were expressed as mean ratios of these rates (experimental rate as a fraction of control rate) with asymmetric 95% confidence limits determined nonparametrically from distributions of bootstrapped ratios. Thus, at all temperatures, exposure to treatments was over a standard period of physiological or developmental time-one lifetime or generation. In rotifers acclimated for many generations to low (12 degrees-14 degrees C), intermediate (19 degrees C), and high (25 degrees-26 degrees C) temperatures, susceptibility to the cyanobacterium and its toxin increased significantly with temperature; ratios of lambda values were 1.5-2 times greater at the low than at the high temperatures. The results indicate that seasonal increases in water temperature, and climate warming, may exacerbate the impact of toxic cyanobacteria on rotifers and perhaps other zooplankton taxa.