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

Data from 35 published studies were collated to examine patterns in the trophic enrichment of 13 C of consumers. Because both delta 13 C and delta 14 N 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 13 C to ecosystem-standardized trophic position ( DELTA delta 15 N) 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 13 C). However, differences were observed in the slopes between delta 13 C and standardized trophic position when data were examined study-specifically: the average trophic fractionation of 13 C 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 13 C enrichment for consumers supports previous findings of a similar continuum existing for zooplankton - particulate organic matter differences in delta 13 C. Possible mechanisms to explain these ecosystem-specific patterns in 13 C 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.