Structure du peuplement des Harpacticides dans le milieuhyporhéique d'un ruisseau des Pyrénées

Abstract

The hyporheic harpacticoids from a 75 m2 area along Lachein Creek, (French Pyrenees), were studied during one year. Seven bi-monthly collections were sampled in the ten quadrats from this area. Twenty one species with nine stygobionts were collected. This assemblage is characterized by temporal stability: no seasonal variations in relative abundance of the main species were detected between the seven collections. Yet, this assemblage has a large spatial heterogeneity. Four groups have been recognized and their distributions are a function of the physiographic environments within the stream channel; two gravel bars, a channel and a stagnant water zone. The gravel bars constitute the favoured environment for harpacticoids. Here, stygobiont species are more abundant than epigeous species. The epigeous species are more important along the periphery of the gravel bars. Hydrodynamic conditions in the hyporheal zone explain this distribution. The most abundant populations with the greatest species richness occur where stream bed permeabilities are greatest. However, at this place, the diversity is lower because of competitive exclusion. © Gauthier-Villars, 1991.