Movement patterns of invertebrates in temporary and permanent streams.

Abstract

Although it has been shown that invertebrates recolonize reflooded temporary streams from permanent refuges, e.g., the hyporheic zone, it has not been shown that they actively move into these refuges as streams dry. Substrate filled cages and drift nets were used to monitor invertebrate movement in two temporary streams and a permanent stream prior to and during drying to determine whether invertebrates leave drying riffles and enter flooded riffles. Invertebrate movement was essentially unidirectional in the permanent stream with downstream drift and with-in-substrate downstream movement dominating. In the temporary stream, movement vertically downward toward the hyporheic zone and upstream movement substantially contributed to a departure from a unidirectional pattern. In addition, prior to stream drying the relative colonization rate was higher and drift rate was lower in the temporary streams than in the permanent stream. During drying of the temporary stream, upstream movement continued to dominate but hyporheic movement was unimportant. Further, the upstream movement did not occur at the end of the riffle where it would lead to migration into non-drying riffles. Thus, even though movement patterns were different in permanent and temporary streams the pattern observed during stream drying would result in the concentration and subsequent death of invertebrates in drying riffles. This observation demonstrates that movement patterns of stream invertebrates do not necessarily result in behavioral avoidance of a dry period of temporary fiffles.