Laminaria hyperborea is an important species of kelp comprising large kelp forests along the Norwegian coast. Large quantities of detritus from these forests are exported to other ecosystems. These exports could support high secondary production in neighboring habitats, such as the intertidal zone. Kelp tissue fragments off the ends of the lamina, is degraded by bacteria and can then potentially be consumed by organisms like benthic filter-feeders. Mytilus edulis and Semibalanus balanoides are two key suspension feeders found in the littoral zone and feed primarily on phytoplankton and organic detritus. Some of this detritus could be derived from L. hyperborea. In order to investigate this, a growth experiment was devised to see how the two filter-feeders responded to different diets. One half of the organisms from each species received L. hyperborea detritus and the other half received a blend of three phytoplankton species: Protoceratium reticulatum, Prorocentrum minimum, and Skeletonema pseudocostatum. The test organisms were housed in aquaria with an artificial seawater system, while control organisms received natural running seawater from Oslofjord. Organisms were fed regularly with measurements of mussel shell length and barnacle shell diameter taken once a month. M. edulis individuals were grouped by small or large size and these measurements were analyzed separately. The large group of mussels on the phytoplankton diet grew significantly more than the detritus diet group. This means that the phytoplankton diet provided a better nutrition source than the detritus from L. hyperborea. There was no significant difference in the growth of small M. edulis between the two diet types. The small mussel group fed L. hyperborea detritus grew just as well as the phytoplankton diet group. There was no difference in size between the diet groups for the barnacles when considering only the effect of diet. Both barnacle diet groups had a significantly smaller size than the control group. Overall, S. balanoides grew very little over the duration of the experiment. The result from M. edulis shows that this species can survive on L. hyperborea detritus and in the case of the small group they can grow equally as well as on a phytoplankton diet. The outcome from S. balanoides indicates that more factors may need to be taken into consideration with this species and its feeding activity. This thesis gives a fundamental aim of investigating the relationship between L. hyperborea and the filter feeding species living in the littoral zone.