Nitrogen Isotopes - analysis, Oceans and Seas, Herbivory - physiology, Fucus - chemistry, Isopoda - physiology, Birds - physiology, Nutritional Physiological Phenomena - physiology, Food Chain, Gastropoda - physiology, Animals, Feces - chemistry, Models, Biological, Finland, Birds - metabolism, Population Dynamics, Enrichment, Ecosystems, Periphyton, Summer,...