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

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research Centre

MDFRC item.

Rotifer emergence from dry billabong sediments was studied from 3 sites on the River Murray floodplain, nearWodonga, northern Victoria, Australia. The sites had different flood histories, ranging from annual to approximately25-year flooding intervals. Half of each sediment type was sterilized by γ -radiation to contrast thecontribution of recruitment from the egg bank with recruitment from passive dispersal. A series of mesocosmswas employed to assess differences between treatments, i.e. sediment sterilization and flood history. Analysisby Canonical Correspondence Analysis and Similarity Percentages suggested that some species were passivelydispersed. Of the 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, maybe more successful in locating passively dispersed taxa than examination of natural temporary waters.