Ecosystem differences in the trophic enrichment of 13C in aquatic food webs

Abstract

Data from 35 published studies were collated to examine patterns in the trophic enrichment of 13C of consumers. Because both delta 13C and delta 14N vary systematically across ecosystems, it was necessary to standardize for such differences before combining data from numerous sources. Relationships of these measures of ecosystem-standardized delta 13C to ecosystem-standardized trophic position ( DELTA delta 15N) for freshwater, estuarine, coastal, and open-ocean and for all aquatic ecosystems yielded regression equations of low predictive capability (average of 20% explained variance in delta 13C). However, differences were observed in the slopes between delta 13C and standardized trophic position when data were examined study-specifically: the average trophic fractionation of 13C was found to increase from + 0.2omicron for freshwater to + 0.5omicron for estuarine to + 0.8omicron for coastal, and to + 1.1omicron for open-ocean food webs. This ecosystem-specific gradient in 13C enrichment for consumers supports previous findings of a similar continuum existing for zooplankton - particulate organic matter differences in delta 13C. Possible mechanisms to explain these ecosystem-specific patterns in 13C enrichment may be related to the relative importance of detritus, heterotrophic respiration, partial reliance on alternative food sources, and lipid influences in the different ecosystems.