Contrasting effects of the invertebrate predator Chaoborus obscuripes and planktivorous fish on plankton communities of a long term biomanipulation experiment
Wissel, B.; Benndorf, J.
published: Oct 20, 1998
ArtNo. ESP141014302001, Price: 29.00 €
In a long-term biomanipulation-experiment, started in 1979, all planktivorous fish were removed from an experimental lake while a reference lake was left unmanipulated. The intermediate response was characterized by a strong increase in both Daphnia biovolume and size, and an increase in the abundance of the invertebrate predator Chaoborus flavicans. After 12 years, the larger and darker C. obscuripes, typical of fishless lakes, successfully colonized and displaced the smaller species C. flavicans within three years. Subsequently in 1995, zooplankton biovolume and size decreased dramatically, caused by heavy predation of C. obscuripes on all zooplankton from small rotifers to large daphnids. Zooplankton biovolume was substantially lower than in an adjacent reference lake dominated by planktivorous fish. In the reference lake also most of the crustaceans were eliminated but a high biovolume of rotifers remained. Phytoplankton biovolume was considerably higher in the experimental lake than in the reference lake, although no evident differences in primary production and Secchi could be detected between the two lakes. We clearly showed that the total absence of planktivorous fish can lead to worse water quality (in terms of phytoplankton biovolume) than a very high biovolume of planktivorous fish.