Seasonal Variability of Meiofaunal Abundance in the Oligo-mesohaline Area of the Gironde Estuary, France

Abstract

The seasonality of meiofauna abundance was examined at an intertidal mud flat located in the oligo-mesohaline reach of the Gironde Estuary, France. Samples were collected weekly for 1 year at two stations located at the lower and the upper level of the mud flat (Stations L and H, respectively). Clear seasonal variations were evident for the meiofauna at both stations. Multivariate analysis revealed that meiofaunal composition, as well as biomass, was mainly regulated by temperature and salinity. Meiofaunal abundances were dominated by harpacticoid copepods at Station H and by nematodes at Station L, with meiofaunal biomass dominated by harpacticoid copepods at both stations, an unusual situation in estuarine muddy sediments. The meiofaunal community response to salinity occurs both as a chronic effect and as an anticipation to estuarine water salinity changes, thus suggesting that the animals response to this factor in oligo-mesohaline areas can also be an acute response to local heavy rains which can influence the meiofauna due to both variations of interstitial salinity and by erosion. Microphytobenthic resources, as estimated by chlorophyll aand pheopigment concentrations, had no strong influence on either meiofauna composition or biomass. Furthermore, evidence is given that microphytobenthic food supply is not a limiting factor to the benthic fauna in the oligo-mesohaline area of the Gironde Estuary.