Context dependent invasion success of rusty crayfish (Orconectes rusticus) in streams

Rusty crayfish, Orconectes rusticus (OR), invasions in lakes and streams represent a model system to study invasion dynamics in contrasting habitats. OR are significantly larger in lakes than streams and invasions are slower in streams. We hypothesize that flow alters invasion dynamics in streams and is modified by crayfish size and prior experience in flow. We predicted OR would perform according to their prior experience in flow, e.g., lakes < low flow streams (LFS) < high flow streams (HFS).  To test the effects of flow, washout water velocity (WWV) of crayfish was determined in a recirculating flume with pebble substrata as flow increased from 0-100 cm/sec. WWV of lake and LFS crayfish (>50 cm/sec) was significantly lower than WWV for HFS crayfish (55-75 cm/sec). WWV was not significantly different between sizes of crayfish from lakes or LFS.  WWV for HFS OR was size dependent with midsized HFS OR (30-40 mm) performing significantly better than small or large (> 30mm and < 40mm carapace length) OR. Morphology of OR did not differ significantly. Behavior of HFS OR was significantly different from lake and LFS OR.  These results suggest flow may be an important factor mediating invasion dynamics of OR in streams.