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

Data from 35 published studies were collated to examine patterns in the trophic enrichment of C-13 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 C-13 was found to increase from +0.2 parts per thousand for freshwater to +0.5 parts per thousand for estuarine to +0.8 parts per thousand for coastal, and to +1.1 parts per thousand for open-ocean food webs. This ecosystem-specific gradient in C-13 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 C-13 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.