Zooplankton generation following inundation of floodplain soils: effects of vegetation type and riverine connectivity

We investigated the potential for zooplankton to emerge following inundation of dry soils on the lower Waikato River floodplain, North Island, New Zealand. Soil cores were collected from native forest remnants, scrub (predominantly Salix spp.) and pasture, and from sites inside or outside of stopbanks, to examine the effects of vegetation type and hydrological disconnection. We hypothesised that more larger-bodied zooplankton would emerge from forested floodplain areas, and that areas with high connectivity with the river would produce more zooplankton. Zooplankton appeared from soil cores within 3 days of wetting and no new taxa arose after 12 days. Community composition differed between vegetation types, with larger bodied cladocerans and copepods dominating forested and scrub sites, and rotifers dominating pastoral sites. Connectivity did not play a statistically significant role in determining community composition. Soil conditions were implicated as important in affecting emergent zooplankton community composition, with copepods and cladocerans characteristic of sites with wetter soils and bdelloid rotifers abundant in open sites with higher soil temperatures. Our findings indicate scrub and forested floodplains can be important areas for large-bodied zooplankton production, and that maintaining vegetative heterogeneity on floodplains may promote trophic subsidies for migrating juvenile fish as floodwaters subside.