Removal of settled sediments and periphyton from macrophytes by grazing invertebrates in the littoral zone of a large oligotrophic lake

1. The resistance and resilience of littoral zone communities to sedimentat ion will depend both on the extent to which sediment deposition affects pro ductivity, and. on interactions within the communities. A series of hypothe ses were set up and tested to examine interactions and feedback mechanisms among deposited sediments, periphyton, macrophytes and grazers in a large o ligotrophic lake subject to fluctuating sediment loadings. 2. Although sediments incorporated into periphyton reduced light availabili ty to macrophytes, periphytic algae were generally the dominant light absor bing component under natural conditions. When grazers were absent, both sed iments incorporated in the periphyton and periphytic algal densities increa sed, and both were then important in reducing light available to macrophyte s. 3. Grazing rate and assimilation efficiency for the dominant grazer, the pr osobranch gastropod Potamopyrgus antipodarum, increased with increasing sed iment content under natural lake conditions to reach a maximum at 10 mg sed iment cm(-2) 4. An increase in sediment incorporation into periphyton films resulted in an increased grazing rate and hence grooming of sediments from macrophytes. 5. Grazing invertebrates can play a major role in maintenance of littoral c ommunities by continuously grooming macrophyte hosts of periphytic algae an d settled sediments.