Hatching from the sediment egg-bank, or aerial dispersing? the use of mesocosms in assessing rotifer biodiversity

Rotifer emergence from dry billabong sediments was studied from 3 sites on the River Murray floodplain, near Wodonga, northern Victoria, Australia. Th e sites had different flood histories, ranging from annual to approximately 25-year flooding intervals. Half of each sediment type was sterilized by g amma -radiation to contrast the contribution of recruitment from the egg ba nk with recruitment from passive dispersal. A series of mesocosms was emplo yed to assess differences between treatments, i.e. sediment sterilization a nd flood history. Analysis by Canonical Correspondence Analysis and Similar ity Percentages suggested that some species were passively dispersed. Of th e 54 species colonizing after 35 days, four were undescribed, one was a new record to Australia, three species had previously been recorded only from Tasmania and five more were new to the study area. Overall, 22% of species were previously unrecorded from the study area. This suggests that habitat poor mesocosms, may be more successful in locating passively dispersed taxa than examination of natural temporary waters.