Somatic and population growth in selected cladoceran and rotifer species offered the cyanobacterium it Microcystis aeruginosa as food

Abstract

The ability of cladocerans and rotifers to utilise the cyanobacterium Microcystis aeruginosa was tested by comparing the somatic and population growth in cultures using Chlorella and Microcystis as food types. Five species of cladocerans (Ceriodaphnia cornuta, Scapholeberis kingi, Moina macrocopa, Daphnia carinata, Simocephalus vetulus) and two species of rotifers (Brachionus calyciflorus, Hexarthra mira) were used in this study. In order to exclude the possibility of poor utilisation of Microcystis due to mechanical interference, single cells of Microcystis, (obtained by sonicating large colonies) were also offered. Experiments were done at 20 °Cs and 30 °C . In all the treatments tested, the population growth rate per day of the cladocerans ranged from -0.715 to 0.612 and that of the rotifers from -1.15 to 0.781. While C. cornuta, S. kingi and S. vetulus could utilise Microcystis, M. macrocopa and D. carinata were extremely susceptible to its toxins. The ability of the cladoceran populations to grow on Microcystis single cells was not related to the body length or gut length alone but to their ratio. The toxic effects of Microcystis were mitigated at the higher temperature. A strain of C. cornuta, collected from a Microcystis-dominated lake, had a higher growth rate on the toxic cyanobacteria suggesting that the tolerance to Microcystis could be a heritable trait. Of the two rotifer species, only H. mira survived and reproduced in some treatments of Microcystis.