Brabrand, A., B. Faafeng & J.P.M. Nilssen. (1987). Pelagic predators and interfering algae: Stabilizing factors in temperate eutrophic lakes. Archiv für Hydrobiologie. 110(4):533-552. Oct 1987.

510941

10.1127/archiv-hydrobiol/110/1987/533 [view]

Brabrand, A., B. Faafeng & J.P.M. Nilssen

1987

110(4):533-552. Oct 1987

Publication

Fundamental and Applied Limnology

Available for editors  

Two large pelagic limnocorrals were installed in Lake Gjersjaen, SE Norway, in 1979 (diam. 10 rn, depth 12 m) and 1980 (diam. 10 m, depth 20 m). The walls consisted of transparent polyethylene foil (thickness 0.15 mm) and the bottom was covered by netting of mesh size 7.9 mm. The corrals were supported by oil-spill booms and surrounded by wooden docks. Temperature, oxygen and p H stratifications in the corrals generally mimicked the conditions in the lake in 1979 and 1980, although the thermocline in the corrals was situated slightly closer to the surface. The effect of fish removal on zooplankton community structure and interfering algae (Oscilhtoria)was investigated during 1979 and 1980. Juvenile roach (Rutilus rutilus) (mostly of age 2+) equivalent to approx. 230 kg ha- were added to one of the enclosures in 1979 and 1000 kg ha- in 1980, while there were no fish in the other corral. The absence of fish had apparently no major effect on water chemistry, phytoplankton and zooplankton, and the enclosures closely resembled the lake during autumn 1979. The experiments in 1980, initiated during the spring phytoplankton peak, gave high abundance of carnivorous cyclopoid copepods in the enclosure without fish. This was followed by even lower numbers of efficient filter-feeders than in the lake, in which fish were the main zooplankton predator. As a result, filter-feeders were unable to influence successional patterns and species composition of phytoplankton, even when roach were absent.

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