The influence of planktivorous fish on zooplankton resting-stage communities in riverine slackwater regions

Murray-Darling Freshwater Research Centre

MDFRC item.

Planktivorous fish are important in shaping zooplankton communities in many freshwater ecosystems, and there is an intrinsic link between the active and resting forms of many zooplankton taxa. However, few field studies have considered the influence of planktivorous fish on zooplankton resting-stage communities, and none have considered this phenomenon in rivers. In two separate but concurrent 12-day experiments, we investigated the effects of Eastern Gambusia (Gambusia holbrooki Girard) and carp gudgeon (Hypseleotris spp.) on zooplankton resting-stage communities in slackwaters of an Australian floodplain river. This was achieved by setting coconut fibre mats on the bottom of the experimental enclosures and later incubating the resting stages captured. A high biomass (2.5 g m(-2)) of Gambusia suppressed the total abundance and diversity of resting-stage microcrustaceans between days 6 and 12, and the abundance of resting-stage Asplanchna spp. throughout the entire 12-day period. Furthermore, a high biomass of Hypseleotris suppressed the total diversity of resting-stage rotifers between days 0 and 6. These response patterns generally reflected changes in active populations according to the fish biomass treatment, rather than changes in dormancy induction by active individuals. This suggests that a high biomass of planktivorous fish can potentially influence zooplankton resting-stage communities in riverine slackwaters in addition to active zooplankton communities due to the inherent association between resting stage and active forms of zooplankton taxa.