Evidence of multi-decadal behavior and ecosystem-level changes revealed by reconstructed lifetime stable isotope profiles of baleen whale earplugs

Biological time series datasets provide an unparalleled opportunity to investigate regional and global changes in the marine environment. Baleen whales are long-lived sentinel species and an integral part of the marine ecosystem. Increasing anthropogenic terrestrial and marine activities alter ocean systems, and such alterations could change foraging and feeding behavior of baleen whales. In this study, we analyzed delta C-13 and delta N-1(5) of baleen whale earplugs from three different species (N = 6 earplugs, n= 337 laminae) to reconstruct the first continuous stable isotope profiles with a six-month resolution. Results of our study provide an unprecedented opportunity to assess behavioral as well as ecological changes. Abrupt shifts and temporal variability observed in delta C-13 and delta N-15 profiles could be indicative of behavior change such as shift in foraging location and/or trophic level in response to natural or anthropogenic disturbances. Additionally, five out of six individuals demonstrated long-term declining trends in delta C-13 profiles, which could suggest influence of emission of depleted (CO2)-C-13 from fossil fuel combustion referred to as the Suess effect. After adjusting the delta C-13 values of earplugs for the estimated Suess effect and re-evaluating delta C-13 profiles, significant decline in delta C-13 values as well as different rate of depletion suggest contribution of other sources that could impact delta C-13 values at the base of the food web. (C) 2020 Published by Elsevier B.V.

Automated summary

Utilizing stable isotope profiles from baleen whale earplugs, this study reconstructed continuous spectra revealing potential behavioral and ecological changes in response to natural or anthropogenic disturbances. The long-term declining trends in δC-13 profiles among most individuals suggest an influence of the Suess effect from fossil fuel combustion. Adjusting for the Suess effect showed significant declines in δC-13 values, indicating contributions from other sources impacting δC-13 values at the base of the food web.