VULNERABILITY OF BRANCHIOPOD CYSTS TO CRUSHING

Ephemeral wetlands, such as vernal pools and playas, have become incre asingly threatened by a variety of destructive human practices, includ ing off-highway vehicle (OHV) activity. Among the resident animals tha t may be adversely affected are the branchiopod crustaceans which prod uce desiccation resistant cysts to withstand the pools' dry periods. W e report a quantitative investigation of the force required to crush i ndividual branchiopod cysts of 8 species: Branchinecta lynchi, B. sand iegonensis, B. mackini, Streptocephalus woottoni, Thamnocephalus platy urus, Linderiella occidentalis, Lepidurus lemmoni, and Triops longicau data. Very small forces of less than 1 newton crushed dry cysts. Wet c ysts were even more fragile; many were crushed under less than 7 x 10( -2) newtons. Differences in vulnerability were found within and betwee n taxa and may be related to cyst morphology. Knowledge of these effec ts should be taken into consideration when developing management strat egies for ephemeral wetlands.