Effects of gut content on δ15N, δ13C and C:N of the macroinvertebrate Mysis diluviana

Stable isotopes have become a popular method for studying aquatic food webs. Lack of laboratory studies and standardized methods, however, may limit the application and interpretation of stable isotope analysis. One procedure applied inconsistently among stable isotope studies for whole body and bulk invertebrate samples is gut evacuation after capture. We evaluated the importance of gut evacuation prior to stable isotope analysis in the omnivorous macroinvertebrate Mysis diluviana. Mysis ranging from 9 to 20 mm were fed a diet of Artemia for 58 days in the laboratory. Following this acclimation period, Mysis with empty guts, full guts of Artemia, and full guts of green algae (Scenedesmus obliquus) were processed for stable isotope analysis of δ15N, δ13C and C:N. We found no significant difference among gut content treatments for any of these metrics. We conclude that gut evacuation is an unnecessary step in stable isotope analysis of Mysis in the size range we investigated.