Egg bank spatial structure and functional size of three sympatric branchiopods (Branchiopoda) in Siangtian Pond, Taiwan

Abstract

Large branchiopods in temporary wetlands produce eggs that hatch in an asynchronous sequence to overcome stochastic hydroperiods. Long-term dynamics between egg replenishment and depletion result in habitat-specific egg bank spatial structures. Unlike earlier studies focusing mainly on the active stages, this study explores the horizontal distributions and functional sizes of the egg banks of three large branchiopods, Branchinella kugenumaensis, Eulimnadia braueriana, and Lynceus biformis, in Siangtian Pond, Taiwan. Superficial sediment was systematically collected from 58 sites in a defined “core area,” and eggs were identified and quantified in 0.5 g sediment aliquots, with ten replicates for each site. The egg density was calculated to estimate the egg bank size and was plotted to show the spatial distribution patterns. We found that of the three species, L. biformis was the most abundant in the egg bank, while the egg bank size of B. kugenumaensis was close to cohort fecundity, indicating limited egg accumulation. Horizontal distributions varied significantly between species, with B. kugenumaensis concentrated centrally at the three deepest sites, E. braueriana aggregated peripherally in less vegetated areas, and L. biformis found predominately in the south. The egg bank spatial structure could be partially explained by the varying inundation area and population maturation times. However, egg floatation and wind action may also be influential.