Spatial and temporal distribution of the zoobenthos community in a woodland pond (Switzerland)

Spatial and temporal changes of zoobenthos composition and density were assessed in a woodland pond, near Geneva (Switzerland), by monthly sampling (during 15 months), on the three main substrates: a submerged macrophyte (Chara sp.), an emergent macrophyte (Typha latifolia stems) and allochthonous detritus (oak leaves).Many taxa showed preferences for one or two of the substrates, as expressed by differences in densities, but few taxa presented an exclusivity for one substrate. Zoobenthos densities (per m² of pond bottom) were largely dominated on all substrates and seasons by Chironomidae and Oligochaeta. Other dense macroinvertebrates included Ostracoda (on Chara and Typha stems), Gastropoda (on Typha stems), Ephemeroptera (all substrates), and Ceratopogonidae (on Typha stems).The magnitude of temporal differences in densities was expressed by the ratio of maximal to minimal monthly densities and reached values between 2.8 to 11.8. On all substrates the highest monthly densities were observed in summer or beginning of autumn. The temporal changes in densities were strongly influenced by the life cycles of the invertebrates: presence of numerous young individuals in summer (for example Cypridopsis vidua, Cloeon dipterum, Caenis horaria, Ferrissia wautieri), and emergence (for example Chironomidae in April). Fluctuations in densities, especially on Chara and leaves, were also attributed to modification of substrate condition (surface availability, stage in the decomposition or senescence process). Temporal fluctuations of densities were compared with other lentic water bodies: highest densities showed a common trend, occurring between end of spring and beginning of autumn.