The response of benthic macroinvertebrates to artificial disturbance: drift or vertical movement in the gravel bed of two Sub-Alpine streams?
Gayraud, Sebastien; Philippe, M ichel; Maridet, Laurence
published: Feb 11, 2000
ArtNo. ESP141014704002, Price: 29.00 €
In most streams, invertebrate recovery following hydrological disturbance is rapid. For three decades, biologists have assumed that recovery after flooding is facilitated by behavioural migration from refugia, particularly from the hyporheic zone. The relevance of this hypothesis was experimentally tested in two medium-gradient streams with porous beds using a new technique that allows the increase of discharge in a 0.20 m2enclosed area. Vertical distribution of benthic macroinvertebrates and drift intensity were compared between disturbed and undisturbed areas. The prediction that after artificial disturbances invertebrate density should decrease on the surface and increase in the hyporheic zone was not supported by the data. Total invertebrate density decreased significantly in the surface layer (0-8cm) but was not significantly different between disturbed and undisturbed areas in the deep layers (8- 60 cm). The same observations were made for most numerous invertebrates such as Chironomidae, Gammaridae and Heptageniidae. The alternative prediction that disturbance should increase drift intensity was supported by field observations. Artificial disturbance enhanced drift intensity and modified drift composition, causing an increase in the relative abundance of Chironomidae pupae and Gammaridae. This study indicates that downward migration of invertebrates within the hyporheic zone during a flood is not always evident and that recolonization may primarily occur by drift from other refugia.