Importance of phlorotannin content and C : N ratio of Laminaria hyperborea in determining its palatability as food for consumers

The importance of the tissue C : N ratio and the content of phlorotannins for the suitability of kelp, Laminaria hyperborea, as food for consumers was tested. Laminas from kelp were sampled in winter. In the laboratory, the kelp was experimentally degraded for 3, 14 and 44 days by kelp-associated bacterial communities under aerobic conditions. The kelp C : N ratio and phlorotannin contents decreased with degradation. The kelp was fed to the kelp-associated amphipods Ampithoe rubricata and Gammarus locusta in no-choice feeding experiments. The growth of amphipods was higher on kelp that was not degraded or degraded for short periods than on kelp degraded for long periods. The results show that the content of phlorotannins in L. hyperborea lamina is of little importance for their suitability as food. An earlier study using kelp with a high C : N ratio showed increased amphipod growth after long degradation and the results from both studies suggest that the C : N ratio of kelp varies greatly with season and the degree of degradation and is important for their suitability as food. Kelp is only palatable when the C : N ratio is not too high or too low.