Effects of small-scale sedimentary patchiness on the distribution of tubificid and lumbriculid worms in Lake Geneva

SUMMARY. 1. The sediment consists of pillow-like formations (0.7 m wide) separated by trenches, 0.2 m wide and 0.1 m deep, over large areas of Lake Geneva (Switzerland).
2. Biomass and total abundance of tubificid and lumbriculid worms were higher on the pillows than in the trenches. Potamothrix vejdovskyi, P. hammoniensis, P. heuscheri and Tubifex tubifex were more abundant on pillows whereas Peloscolex velutinus and Stylodrilus heringianus were relatively more abundant in the trenches.
3. These differences between worm communities suggested that organic sedimentation was higher on the pillows. Sedimentological analyses confirmed this interpretation.
4. Results of large-scale surveys can be biased if sampling design is not adapted to such small-scale patchiness.