Stoichiometric variation in C:N, C:P, and N:P ratios of littoral benthic invertebrates

Abstract

Nutritional constraints on herbivores are important factors structuring food webs. Our study presents field data on the nutrient content of benthic invertebrates from Lake Erken (Sweden). The most abundant benthic invertebrates of the littoral community were sampled in 3 seasons at 5 sites to examine the influence of spatial and temporal variation of abiotic conditions on invertebrate C:N:P stoichiometry. The relationships between nutrient ratios and dry mass (DM) of invertebrates were evaluated using regression analysis. Nutrient ratios of periphyton, sampled in an earlier study, were compared to those of benthic invertebrates. C:N, C:P, and N:P ratios differed among invertebrate taxa. Coleoptera had relatively high C:N, C:P, and N:P ratios, whereas Isopoda had low C:N, C:P, and N:P ratios. Nutrient ratios differed with respect to season and location. C:P and N:P ratios were significantly lower and C:N ratios were significantly higher in autumn than in spring and summer. C:P and N:P ratios increased as a functions of invertebrate DM when all taxa were analyzed together. C:N and C:P ratios of periphyton were higher than those of benthic invertebrates, but N:P ratios were similar. Our results suggested that benthic invertebrates have taxon-specific C:N and C:P ratios, but the seasonal variability in ratios indicated that littoral invertebrates were rheostatic rather than homeostatic with respect to nutrient stoichiometry. The temporal and spatial variation in grazer nutrient content must be taken into account when applying stoichiometric theory to benthic food webs.