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Reduction of benthic macroinvertebrates due to waterfowl foraging on submerged vegetation during autumn migration
Marklund, O.; Sandsten, H. (2002). Reduction of benthic macroinvertebrates due to waterfowl foraging on submerged vegetation during autumn migration. Aquat. Ecol. 36(4): 541-547
In: Aquatic Ecology. Springer: Dordrecht; London; Boston. ISSN 1386-2588, more
Peer reviewed article  

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Keyword
    Fresh water

Authors  Top 
  • Marklund, O.
  • Sandsten, H.

Abstract
    If present in large numbers, as during migration, herbivorous waterfowl may reduce the amount of submerged vegetation. Because the vegetation is a key factor in shallow eutrophic lakes, removal of the green biomass can be expected to affect also other biota that depend on the vegetation. We conducted an experiment to determine how the abundance of chironomids and Pisidium sp. were affected by intense foraging of waterfowl on the submerged plant Potamogeton pectinatus. This was done in Lake Ringsjön in southern Sweden, during the autumn migration of the birds. Three treatments, replicated six times, were used: (i) closed cages that excluded all waterfowl, (ii) semi-open cages that excluded only large waterfowl (geese and swans), and (iii) open plots where all waterfowl could freely enter. Waterfowl densities were monitored during the experiment. The results suggest that the foraging of large waterfowl (swans) had a clearly negative effect on macroinvertebrate abundance and aboveground biomass of P. pectinatus. At the end of the experiment, the density of chironomids was about 46% lower in the open than in the closed cages. In general, the density of Pisidium sp. tended to be lower in the open plots. Small waterfowl alone did not seem to affect either the vegetation or macroinvertebrates. We suggest that the Pisidium sp. was influenced at an early stage of grazing, when waterfowl foraged on aboveground biomass, whereas chironomids were affected at a later stage, when swans were digging for below-ground tubers.

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