Interactions between crayfish, benthic invertebrates, macrophyte roots and sediment in a littoral zone

The littoral zone is subject to both top-down and bottom-up control. In an experiment in Trout Lake, Wisconsin, plant roots were seen to be the central component of interactions with crayfish and macrobenthos. Consequently, crayfish predation and feeding of benthic macroinvertebrates were examined with respect to the presence or absence of plant roots. Six sets of three cages, 1 without crayfish, 1 with three times natural crayfish number (6 ind. per m 2 ) and 1 wall-less reference were placed on lake bottom in the littoral zone. Each cage was divided to halves with the benthos in one half being fed and not being fed in the other half. Each half was further halved to two quarters with macrophytes in one quarter being cut in the other not being cut. Three samples of macrobenthos were taken from each quarter in July and August 1991. Crayfish impact on benthic organisms was significant in August regardless of the presence or absence of plant roots. Feeding significantly influenced chironomid size in July, also without any interaction with plant roots. Macrophyte cutting negatively affected invertebrate abundance and it was significant both in July and August. The results confirmed the importance of plant roots for invertebrates abundance. Presence of live plant roots seemed to be an important factor for structuring the benthic invertebrate community apart from the well-known effects of feeding and predation.