Research Article Zooplankton dynamics from inundation to drying in a complex ephemeral floodplain-wetland Cassandra S. James 1 * , Martin C. Thoms 2 and Gerry P. Quinn 3 1 Australian Rivers Institute, School of Environment, Griffith University, Nathan, Queensland 4111, Australia 2 Riverine Landscapes Research Laboratory, School of Resource and Environmental Science, University of Canberra, ACT 2601, Australia 3 School of Life and Environmental Sciences, Deakin University, Warrnambool, Victoria 3280, Australia Received: 25 July 2007; revised manuscript accepted: 14 March 2008 Abstract. Ecological responses to wetting and drying in dryland river floodplain systems are often described in terms of “boom” and bust”. We suggest that patterns in floodplain species abundances and assemblage struc- tures will be closely linked to the changes in spatial habitat heterogeneity that accompany flooding and drying phases. This study examined the responses of zooplankton through a wetting and drying cycle in a complex floodplain-wetland system in semi-arid Aus- tralia, the Narran Lakes. We illustrate the complexity of the zooplankton “boom” and “bust” response. Total densities of zooplankton varied considerably over time and patterns were very dissimilar between sites with abundances varying from <30 animals/L to over 4000 animals/L. We detected different patterns in the pro- portion of variance in abundances of the broad taxo- nomic groups (rotifers, cladocerans, ostracods, calanoid copepods, cyclopoid copepods and nauplii) explained by time and space. Site explained the highest proportion of variation in cladoceran and ostracod abundances, where- as variance in calanoid abundances was explained predominantly by time since inundation. Variation in the abundances of the remaining groups was explained largely by the site by time interaction. Zooplankton assemblages were observed to diverge during drying with highest between-site dissimilarities in assemblage structure occurring during the later stages of drying. Such high spatial and temporal variability in zooplank- ton abundances and community composition could have important consequences for consumers such as fish and some wetland birds that utilize these ephemeral systems for feeding and breeding while they are inundated. Key words. Aquatic microinvertebrates; semi-arid; flooding; dryland rivers; variability; Australia. Introduction Floodplains are dynamic features of the riverine landscape characterized by periodic inundation. This is exemplified in dryland systems of semi-arid and arid-zones where flows are highly variable and unpredictable (Reviewed in Graf, 1988; Walker et al., 1995). Temporal patterns of wetting and drying reflect the variability of over-bank flows (Flood pulses sensu Junk et al., 1989) and are concomitant with changes in the spatial organisation of habitats as floodwaters rise and recede. The resulting shifting mosaic of habitats (Stanford et al., 2005) promotes a high diversity of biota adapted to these changing conditions. * Corresponding author phone: +61 7 37357308 ; fax: +61 7 3735 7615; e-mail: c.james@griffith.edu.au Published Online First: July 1, 2008 Aquat. Sci. 70 (2008) 259 – 271 1015-1621/08/030259-13 DOI 10.1007/s00027-008-8034-0  Birkhäuser Verlag, Basel, 2008 Aquatic Sciences