P3.41 Friday, Jan. 6 Fresh vs. Aged Kelp: Feeding Preferences of Red Urchins RAYMOND, W.W.*; DUGGINS, D.O.; DETHIER, M.N.; Oregon State University; Friday Harbor Laboratories, University of Washington; Friday Harbor Laboratories, University of Washington firstname.lastname@example.org
Kelps create a large amount of biomass in nearshore temperate marine ecosystems. Kelps also provide structure, habitat and food to many organisms. However, attached kelps are only minimally consumed by large herbivores. When kelps detach from the rock their biomass is transported elsewhere in the ecosystem, providing a spatial subsidy of carbon to consumers in other habitats. One consumer is the red urchin, Strongylocentrotus franciscanus, which occurs from the intertidal to 120m depth. Urchins are known to feed on kelps transported as drift, and due to their low assimilation efficiency, urchin waste becomes a viable food source to other benthic organisms. Drift kelps gradually degrade as they are transported into deep water, but the effect of degradation or aging on kelp palatability to urchins is not well known. I investigated the feeding preferences of red urchins to fresh or aged kelps: Nereocystis luetkeana, Agarum fimbriatum, and Saccharina subsimplex. I simultaneously offered a fresh and aged sample of each kelp species to urchins and recorded which sample was bitten first. My results show strong preferences for aged N. luetkeana but for fresh A. fimbriatum and S. subsimplex. Due to their preferential feeding behavior, urchins act as a biological filter in the spatial subsidy, therefore serving a critical role in determining the rate at which kelps are integrated into the food web.