Meeting Abstract

P3.65  Sunday, Jan. 6  Food choices and values for a benthic herbivore, Idotea wosnesenskii BURGESS, S.A.*; EISENLORD, M.E.; GALLOWAY, A.W.E.; DETHIER, M.N.; University of Michigan; University of Washington, Friday Harbor Laboratories; University of Washington, Friday Harbor Laboratories; University of Washington, Friday Harbor Laboratories shelbyab@umich.edu

Spatial subsidies of aged detrital seaweed from habitats of high primary production may provide a significant source of energy to adjacent food webs. Previous studies indicate nearshore consumers use aged algal material as a food source. As aging occurs, algae are thought to increase in food value due to bacterial colonization. To test this, two experiments were conducted. The first examined preference of aged versus fresh thalli of two different kelp species, Nereocystis luetkeana and Agarum fimbriatum, in laboratory feeding experiments. Adults of Idotea wosnesenskii, an intertidal isopod common to the Pacific Northwest, were given four treatments of aged and fresh kelp of both species. Significantly more N. luetkeana was consumed than A. fimbriatum, but contrary to expectations, there were no significant differences in consumption of fresh versus aged tissue for either species. The second experiment was a 10 week long feeding trial with newly hatched I. wosnesenskii to determine growth rates on five different diets: aged N. luetkeana, fresh N. luetkeana, and fresh Ulva spp., Fucus gardneri, and Mazzaella splendens. Diets of algae with anti- herbivore defenses, one chemical (F. gardneri) and one mechanical (M. splendens), resulted in significantly lower growth rates than algae without these defenses. There was not a significant difference in growth rates between aged and fresh N. luetkeana. Our results suggest the species of algae may be more important in providing useful subsidies to benthic grazers than the degree of aging. The effects of aging on the nutritional value of algal blades needs further investigation.