Seasonal dynamics of benthic macroinvertebrate communities in the Lower Ard�che River (France)

Abstract

Seasonal sampling at six locations on the Lower Ardeche River was effected irregularly during 1982, 1983 and 1984. The seasonal structure of the taxa-sample matrix, much more important than sample location, is demonstrated using graphical interpretation. The Mediterranean aspect of the lower reaches of the Ardeche River is pointed out through its community structure which includes species often collected in other typical Mediterranean streams, e.g. Oligoneuriella rhenana, Ephoron virgo, Ecdyonurus dispar, E. insignis, Choroterpes picteti. Water temperature and day length were the determinant influences on seasonal variations in population structure of benthic macroinvertebrates. Three periods were distinguished: water (November to April), spring (May, June and beginning July) and summer (end of July to October). Spring and autumnal spates marked the limits of the summer and winter periods. Hence, annual fluctuations of this seasonal typology may occur in response to the hydrological regime.