PARENT SESSION
Oral Session 91: Aquatic Ecology VII: Communities and Trophic Structure.
Presiding: D Yee and C Swan
Thursday, August 5, 8:00 AM to 11:30 AM, Meeting Room A 105.
Effects of replicated large-scale riparian manipulations on an Olympic Peninsula river food web.
Wootton, J. Timothy*,1, 1 University of Chicago, Chicago, IL
ABSTRACT- Environmental management strategies often focus on single species, but may affect the broader food web in which the target species is imbedded. I explored food web impacts of a replicated series of large-scale (100-300 m) riparian zone manipulations designed to create salmon habitat by increasing the future input of recalcitrant conifer logs into the Pysht River, Olympic Peninsula, Washington. In the short term, removing riparian vegetation on one side of experimental reaches reduced leaf litter input by 65%, but increased algal production 10-fold compared to interspersed unmanipulated reaches. In response, algal biomass increased 4-fold, invertebrate abundance increased 3-fold, and juvenile salmonid density increased 26%. Summer water temperature, nutrient levels, and habitat structure did not differ between treatments. Nutrient addition experiments revealed no evidence of nutrient limitation on algal production in either treatment. Stable isotope analysis indicated high (85%) contributions of algal production to juvenile salmonids in manipulated reaches, a modest (8-11%) contribution of adult salmon carcasses in both treatments, and an unexpectedly high contribution of algal production from treated reaches to untreated reaches (62-66%). These results indicate that management of riparian vegetation for woody debris input also substantially alters the energy base of river food webs, that algal production provides an important energy base for these food webs, and that carefully introducing limited hotspots of algal production within the context of intact riparian corridors may boost juvenile production of stream-rearing salmonids.
Key words: food web, salmon, riparian zone, productivity