Seasonal Responses of Crayfish to Stream Drying

Climate change is expected to cause prolonged droughts and more severe spates.  The Ouachita Mountains already experience seasonal droughts from May to October.  Endemic crayfish have evolved to survive local conditions; however, the mechanisms used to survive extreme conditions and the timing are largely unknown.  Understanding drought responses will allow us to infer how climate change may impact crayfish persistence.  We used passive integrated transponder (PIT) tags to track individual crayfish movements and assess microhabitat use in four streams during the transition period from spring to stream drying in early summer.  We systematically searched for PIT-tagged crayfish biweekly using a backpack PIT tag reader. We found that Orconectes palmeri longimanus migrated to pools whereas O. menae burrowed into riffles and runs.  Migration and burrowing began well before the streams became intermittent.  Crayfish typically used areas with cobble and boulder substrates that contained limited sediment and organic matter.  Our results indicate that some crayfish species move to deeper water while others burrow to avoid harsh summer, drying conditions. It is unclear how long these crayfish survive under these conditions or what the fitness advantage is between the two basic behavioral responses.