Variation in dynamics of interstitial populations of Niphargus and Pseudoniphargus stygobite amphipods at the karst/floodplain interface Variations des effectifs de populations interstitielles de Niphargus et de Pseudoniphargus amphipodes stygobies a linterface karst/plaine alluviale
Essafi, K.; Mathieu, J.; Chergui, H.
Memoires de Biospeologie. Decembre; 24 15-24: 51
The spatial and temporal variations of the stygobite amphipods Niphargus (France) (2 stations) and Pseudoniphargus (Morocco) (1 station) populations were studied at the karst/floodplain interface. One station (Verna, France) was supplied by karst water. The other two stations (Pissoir, France, and Grotte du Chameau, Morocco) were supplied by both karst and surface waters. The dynamics of the populations was found to depend on several interacting factors. The structure and restoration of French populations after a spate was related to geological characteristics. Restoration was slower and more difficult in the sediment located at the base-level of the massif (Verna) than at an overflow level (Pissoir). In contrast, the Moroccan population remained stable in the absence of strong spates. The location of the sediments also influenced the occupation of interstitial habitats. Both in France and Morocco, stations supplied with karstic water contained stygobite amphipods whereas other stations almost only had epigean species. In addition, at the Pissoir station, the number of individuals was higher at the main outflow, but also on the bank opposite the outlet. The variability of the number of individuals at different depths was not the same in both countries. Numbers of Pseudoniphargus increased with depth whereas numbers of Niphargus globally decreased with depth in the Pissoir station, but the gradient varied according to the samples. The distribution of Niphargus seemed to be random at the station mainly supplied by karst water (Verna). The correlation between abundance of individuals and discharge was strongest with discharges two or four days before sampling.