Resistance of crayfish (Procambarus spp.) populations to wetland drying depends on species and substrate

Abstract

Wetland or stream drying can be a severe disturbance for aquatic animals, but the severity of a drying disturbance is context dependent. We used a controlled drying experiment to investigate the resistance of populations of 2 crayfish species (Procambarus fallax and Procambarus alleni) found in south Florida wetlands in 3 sediment types (sand, marl, and peat). The species had different putative burrowing abilities, and we tested the hypothesis that the severity of drying disturbance for populations of burrowing crayfish would be species and substrate dependent. Observations of initial burrowing success indicated that the species could burrow equally well in peat, whereas P. alleni burrowed more effectively than P. fallax in marl and sand. No P. fallax burrowed in the dense sand substrate. The number of crayfish surviving 2 mo underground was a function of particular combinations of species and substrate. Survival of both species was high in peat (∼66%) and similarly high for P. alleni in marl. Survival of P. fallax in marl was considerably lower (31%), and no P. fallax survived in sand. Despite their initial burrowing success, only a few P. alleni survived in the sand in shallow burrows. Survivors of both species showed some loss of body mass from initial conditions, but P. fallax lost relatively more mass. The substrate-specific survival of P. fallax helps explain their persistence at relatively high densities in peat-dominated wetlands that dry every 1 to 3 y and their small populations in marl-dominated marshes with similar drying frequencies. Attempts to explain or forecast the net effects of wetland drying for crayfish populations and other burrowing animals should consider that resistance to drying disturbances will depend on characteristics of both species and substrate types. These considerations have important implications for hydrological restoration of aquatic ecosystems that have pronounced gradients of hydrology and substrates.