Meiobenthic community patterns of oligotrophic and deep Lake Constance in relation to water depth and nutrients

Between February and April 2004, 48 sites in Lake Constance (Germany) were investigated to determine the distribution of the meiobenthic community, including 16 sites from the sub-littoral (13 -30 m water depth), 16 sites from the profundal (31-99 m) and 16 sites from the deep profundal (100-250 m). Lake-wide analysis showed no simple distribution pattern, but rather a heterogenic meiobenthic community composition, with nematodes representing the dominant group (48.7 %), followed by rotifers (27.7 %), harpacticoids (7.7 %), copepods (5.0 %), oligochaetes (3.7 %), ostracods (3.1 %), nauplii (1.9 %) and tardigrades (1.2 %). The relative abundances of all other investigated meiobenthic groups (cladocerans, chironomids, arachnids, gastrotrichs) were below 1 %. The densities of meiobenthic organisms varied greatly between sites, with nematodes reaching up to 3,336,676 and rotifers up to 6,357,008 individuals per m(2). The abundances of most organisms varied significantly between the different water zones. Nematodes, copepods, nauplii and cladocerans, however, were equally distributed between sub-littoral and the profundal zones. Organisms showed their highest levels of abundance in the sub-littoral zone, with the exception of harpacticoids and ostracods, which were most abundant in the profundal and deep profundal respectively. A multivariate statistical analysis revealed that besides Chl-a explaining 47 % of the variance degenerated algae, water depth, mean grain size, organic carbon, C/N ratio and total phosphorus were significantly correlated with lake-wide community structure. In the sub-littoral, mean grain size was the most important parameter explaining 25.4 % of the variance, while in the profundal Chl-a (29.4 %) and in the deep profundal algae pigments (38.6 %) were the most important parameters for meiofaunal distribution and environmental variables.