Dl. Nielsen et al., Impact of water regime and fish predation on zooplankton resting egg production and emergence, J PLANK RES, 22(3), 2000, pp. 433-446
The emergence of zooplankton from ephemeral areas upon re-wetting has been
suggested as a significant contributor to billabong productivity. Sixteen e
xperimental billabongs were designed to test two hypotheses (i) that changi
ng the pattern of flooding alters zooplankton abundance within billabongs,
and (ii) the presence of small planktivorous fish alters the zooplankton co
mmunity structure and diversity within billabongs. Results indicated that f
looding caused microcrustaceans to increase in abundance but not rotifers.
This response was not modified by changing the time of flooding. The presen
ce of the planktivorous fish had only a small influence on the structure of
rotifer assemblages, whereas microcrustacean assemblages became dominated
by juveniles. Emergence of rotifers and microcrustaceans from sediment take
n from the experimental billabongs and incubated under controlled condition
s indicated the existence of a large reservoir of resting stages. The numbe
r of resting stages in the sediment had not been modified by changing the s
eason of flooding in the experimental billabongs, but it was modified by pe
rmanent inundation, which may have removed environmental cues. The presence
of planktivorous fish also appeared to influence the number of resting sta
ges that accumulated in the sediment. Emergence under stable laboratory con
ditions was rapid. This was not the case under more variable natural condit
ions.