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

Abstract

Egg densities were monitored in the dry sediment of four desert rock pool populations of the fairy shrimp Branchipodopsis wolfi over different years/seasons. Egg densities varied according to pool and season/year between about 1,000 and 220,000 eggs per m 2 . This converts to population sizes of between about 200 and 500,000 viable diapausing eggs per pool. Egg densities are within the range of 10 3 to 105 eggs per m 2 usually measured for other zooplankton species with egg banks. Egg densities were associated but not 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 linked with maturation rate and average brood size of the respective populations. Egg densities fluctuate in a partially asynchronosus way among the pools suggesting that factors other than chances for recruitment are also important in controlling egg bank dynamics. The large variance (CV ≥80 %) in egg densities over the seasons in unvegetated pools with loose and sparse sediment in comparison with vegetated pools (CV<40%) with compact sediment holding the eggs, is suggestive of the overriding importance of stochastic passive dispersal by wind or overflows. Earlier reproduction and larger average broods in the short-lived pools also weaken a positive correlation between habitat suitability and egg bank density. The relatively high egg densities of B. wolfi egg banks illustrate the effectiveness of the reproductive and hatching characteristics of this species to successfully persist in this extreme type of temporary habitat. This is the first study on egg bank dynamics in large branchiopods.