Attempts to re-colonise water insects in German brooks

Abstract

Attempts were made to reintroduce water insects (five stonefly species and one mayfly species) into several third order streams in Rhineland-Palatine and Hessen, Germany. All these streams had been strongly affected by waste water and rubbish and had lost most of their macroinvertebrates. As a consequence of the installation of several purification plants in the past three decades, water quality has improved. Since no stoneflies returned, 700–1300 eggs of three different species (Isoperla goertzi, I. oxylepis, and I. grammatica) were exposed in the Selz brook (1997). In February 1998 a few larvae and in 1999 about 10,000 eggs of Perla marginata were added in the Walluf brook, and in 1998, 500 larvae of Oligoneuriella rhenana each in the Ruwer, Alf and Elz brooks. After 10 years, I found only one single larva of Perla marginata in the Walluf brook. In the laboratory, the total number of eggs produced per female could be determined by rearing. On that basis coupled with the assumption of about 3% survival chances for the embryonic and larval development and of about 50% survival chances for the adult females, it was calculated that at least two females of I. goertzi, eight females of I. oxylepis and seven females of I. grammatica were required to found a new and sustainable population.

Keywords:

• egg production
• egg number for re-colonisation
• Isoperla
• Perla
• Oligoneuriella

Acknowledgements

I thank Mrs U. Guschlbauer for careful analysing of the water samples with HPLC and for further help in the laboratory. I also thank Mr K. Banten (STAWA Mainz) for permission to use the water gauge station for the storage of measuring instruments and Mr R. v. Scharpen for language assistance. The paper benefited from the comments of an anonymous referee.