CHANGES IN THE STRUCTURE OF SUBTERRANEAN AQUATIC POPULATIONS OF THE KARSTIC SYSTEM OF OUED-ZEGHZEL (EASTERN MOROCCO)

This study focuses on the changes in space and time, under the warm Me diterranean climate, of the structure of interstitial aquatic populati ons at the karst/floodplain interface of the Beni-Snassen karstic syst em (Eastern Morocco). Artificial substrates buried within the sediment were used. Twenty three taxa were identified in the system, including 4 stygobite species. Assemblage composition and total abundance remai ned relatively consistent over time. However abundances were lower dur ing low-water periods than during high-water periods. Between-station analysis shows the influence of the karstic water supply on the qualit y and, to a lesser degree, the quantity of the fauna. Stations supplie d with karstic water contained stygobite species, whereas other statio ns only had epigean species. The structure was also characterized by a vertical gradient with a decrease of diversity and individual numbers down to a depth of 0.3 m. The deeper 0.2 m showed stable values, whic h differed according to karstic or surface water supply. Pseudonipharg us n. sp. was abundant in the stations supplied with karstic water, le ss common where karstic and surface water occurred together, and absen t in stations only supplied with surface water. Unlike the epigean spe cies, the numbers of Pseudoniphargus n. sp. increased with depth.