Little Indication of Human Influence in 150-year Stable Isotope Fish Record from the Coastal United States
Citation:
Kreakie, B., A. Oczkowski, M. Gutierrez, M. Pelletier, M. Charpentier, E. Santos, AND J. Kiddon. Little Indication of Human Influence in 150-year Stable Isotope Fish Record from the Coastal United States. US Regional Association of the International Association of Landscape Ecology, Fort Collins, Colorado, April 07 - 11, 2019.
Impact/Purpose:
Changes in stable nitrogen and carbon isotopes in fish tissue were used to evaluate how human sources of nitrogen impact coastal production and food webs. Fish tissue measurements were compared from a 2015 survey of all major estuary in the United States as part of the US Environmental Coastal Condition Assessment against tissue samples from fish achieved at the Smithsonian Nation Museum of Natural History (1854 through the 1990s). Larger scale geographic variables like State, longitude, and latitude were among the best predictors of isotope values. Our results underscore the importance of characterizing the baseline and timeline of human impacts associated with a coastal water body of concern, particularly during the planning of restoration efforts or when interpreting ecological impact studies.
Description:
Anthropogenic nitrogen (N) inputs dominate global N cycles, particularly in fluvial systems. Negative impacts of this enrichment on downstream estuaries are well documented. Efforts at N reductions are increasingly successful but ecosystem response trajectories are unclear. To document continental-scale coastal food web N-dynamics prior to large increases in human N-loads, we sampled 208 fish from a Smithsonian archival collection, collected from coastal waters across the conterminous U.S., with a mean collection year of 1914. The archival fish were compared with 526 samples collected in 2015 from 125 estuaries also along the U.S. coastline. We used stable isotopes of N (δ15N) and carbon (δ13C) as a proxy for human inputs and organic matter sources. Landscape measures from 1910 and 2012 census data, fish life histories, and basic estuarine geography were used as predictor variables in random forest models of isotope values. State, latitude, and fish trophic level were consistently the most important predictors, while human impacts played a lesser role. When the fish were collected (~1914 vs 2015) was not an important predictor, rather where the fish was collected was the best predictor of N source. The model results illustrate the important role of large scale patterns play in coastal food web dynamics and underscore the importance of offshore N-sources to coastal food webs.