Macro algae contribute to kelp forest C/N nutrient circulation primarily as detritus, maintaining high primary productivity in local food web. Changes in overall δ¹³C, δ¹⁵N signatures and C content, N content, C/N ratios of five dominating kelp(U. pertusa, C.tenuissima, G.livida, S.vachellianum and H.fusifarme) litters in litter bags during degradation were examined. Kelp litters completely rotted over 42 days in the field near Gouqi Island, both organic C content, N content and C/N ratios were depleted after decomposition, as for δ¹³C and δ¹⁵N, there was no significant variation. We divided the whole kelp degradation into two periods which are leaching degradation period (0-11 days) and microbiological degradation period (11-42 days). Furthermore, trophic level changes by 0.4 in four benthonic herbivores as a result of degradation of macroalgae. It's a significant deviation in macroalgae based kelp bed ecosystem food web establishment.