Microcrustaceans in ephemeral wetlands produce dormant eggs to escape prolonged dry conditions. Upon re-inundation, dormant eggs can hatch from the egg bank. However, not all eggs will hatch at once. Incomplete hatching can reflect bet-hedging strategies, but also the presence or absence of environmental cues to stimulate hatching. Effective environmental cues should ‘predict’ the suitability of conditions created by inundation for survival and recruitment. Environmental change is likely to influence the presence of appropriate environmental cues and how well cues ‘predict’ suitable conditions for hatched microcrustaceans. This study examines the effects of environmental cues likely to change for wetlands in the future – temperature and water depth.
Surface sediments were collected from dry anabranches of the Macintyre River floodplain subject to flooding frequencies ranging from ~4 to 0.5 pa. Samples were inundated under two temperature regimes (warm and cool) in mesocosms of two depths (shallow and deep). Hatched microcrustaceans were sampled weekly for six weeks.
Microcrustacean abundance and assemblage composition varied by temperature but not depth. While the total numbers hatched were greater under warm conditions, the effects of temperature varied over time. Numbers hatching early in the inundation period were greater under warm conditions, but by weeks 5 and 6, numbers hatching under cool conditions exceeded those under warm conditions. In addition, the temperature has a greater effect on non-ostracods hatching as 144% more non-ostracod hatched from the warm condition than cool. Thus, changes to temperature during inundation periods arising from global climate change or river flow regulation are likely to influence the number and assemblage composition of microcrustaceans, especially non-ostracods hatching from flooded sediments in floodplain wetlands which will influence food availability for larval and juvenile native fish and hence recruitment.
Keywords: Microcrustaceans, egg bank, temperature, water depth.