Egg bank dynamics in anostracan desert rock pool populations (Crustacea : Branchiopoda)

Egg densities were monitored in the dry sediment of four desert rock pool p opulations of the fairy shrimp Branchipodopsis wolfi over different years/s easons. Egg densities varied according to pool and season/year between abou t 1,000 and 220,000 eggs per m(2). This converts to population sizes of bet ween about 200 and 500,000 viable diapausing eggs per pool. Egg densities a re within the range of 10(3) to 10(5) eggs per m(2) usually measured for ot her zooplankton species with egg banks. Egg densities were associated but n ot significantly correlated with chances for successful recruitment in each of the pools as estimated from direct observations of pool hydrocycles and from pool morphometry. Egg bank densities were also not significantly link ed with maturation rate and average brood size of the respective population s. Egg densities fluctuate in a partially asynchronosus way among the pools suggesting that factors other than chances for recruitment are also import ant in controlling egg bank dynamics. The large variance (CV greater than o r equal to 80 %) in egg densities over the seasons in unvegetated pools wit h loose and sparse sediment in comparison with vegetated pools (CV <40 %) w ith compact sediment holding the eggs, is suggestive of the overriding impo rtance of stochastic passive dispersal by wind or overflows. Earlier reprod uction and larger average broods in the short-lived pools also weaken a pos itive correlation between habitat suitability and egg bank density. The rel atively high egg densities of B. wolfi egg banks illustrate the effectivene ss of the reproductive and hatching characteristics of this species to succ essfully persist in this extreme type of temporary habitat. This is the fir st study on egg bank dynamics in large branchiopods.