Diversity and vertical distribution of nematode assemblages: the Saguenay fjord (Quebec, Canada)

Three stations were sampled for a meiofaunal survey in the Saguenay fjord's inner basin (Quebec, Canada). Nematodes were the dominant taxon accounting for 90 % of total individuals. Twenty nematode families and 55 genera were found. Cluster analysis showed two different depth- segregated nematode assemblages, one in the surface layer (0-2 cm) and the other in the subsurface layer (2- 10 cm) of the sediment column. A comparison between abundance and biomass vertical distributions showed that smaller individuals were dominant in the surface sediment layer, while larger individuals dominated in subsurface sediment. Selective deposit-feeders were the most abundant feeding group, while epigrowth-feeders were dominant in terms of biomass. Diversity tended to decrease in downstream areas of the fjord. Species composition and size spectra at the three stations suggest the succession of different meiofaunal communities along the fjord. Abundance-biomass comparison (ABC) plots suggested that upstream areas were moderately disturbed. The difference between Shannon's index in terms of abundance and biomass (H'delta = H'abund - H'biom) is suggested to be a useful tool in detecting environmental disturbance