Some Adaptations of Limnadia stanleyana King (Crustacea: Branchiopoda: Conchostraca) to a Temporary Freshwater Environment

Abstract

L. stanleyana inhabits some temporary rain-water pools in eastern New South Wales. Generations of this conchostracan are frequently destroyed before they can reproduce because the rainfall of the area is unpredictable and irregular in occurrence. Eggs are drought-resistant, but free-swimming stages are killed by drying. Dispersal powers are low and pools are not usually recolonized after they dry and refill. Hatching occurs only soon after pools fill after being dry or nearly dry because environmental conditions are suitable at this time. This maximizes the time available for the drought-sensitive stages to grow and produce resistant eggs before the pools dry. After being laid, eggs fall to the mud of the pools and become dispersed through it. Not all hatch when the pools fill; many remain as a reserve in the mud. This protects the population from extinction in the event of desiccation killing one or more generations before they reproduce. Eggs in reserve do not hatch because they are in an unfavourable environment. Conditions in mud are not known, but darkness and low oxygen concentration were both found to inhibit hatching. The effect of these factors probably varies in intensity down from the surface of the mud. This mud circulates when pools contain water and the process ensures that some eggs are always in a location suitable for hatching should filling of the pool occur. The reserve cushions the effect of population crashes. Populations cannot survive in pools that do not contain water long enough for the species to build up a reserve of eggs.