Ecological regime shift drives declining growth rates of sea turtles throughout the West Atlantic.

Abstract

Somatic growth is an integrated, individual-based response to environmental conditions, especially in ectotherms. Growth dynamics of large, mobile animals are particularly useful as bio-indicators of environmental change at regional scales. We assembled growth rate data from throughout the West Atlantic for green turtles, Chelonia mydas, which are long-lived, highly migratory, primarily herbivorous mega-consumers that may migrate over hundreds to thousands of kilometers. Our dataset, the largest ever compiled for sea turtles, has 9690 growth increments from 30 sites from Bermuda to Uruguay from 1973 to 2015. Using generalized additive mixed models, we evaluated covariates that could affect growth rates; body size, diet, and year have significant effects on growth. Growth increases in early years until 1999, then declines by 26% to 2015. The temporal (year) effect is of particular interest because two carnivorous species of sea turtles-hawksbills, Eretmochelys imbricata, and loggerheads, Caretta caretta-exhibited similar significant declines in growth rates starting in 1997 in the West Atlantic, based on previous studies. These synchronous declines in productivity among three sea turtle species across a trophic spectrum provide strong evidence that an ecological regime shift (ERS) in the Atlantic is driving growth dynamics. The ERS resulted from a synergy of the 1997/1998 El Niño Southern Oscillation (ENSO)-the strongest on record-combined with an unprecedented warming rate over the last two to three decades. Further support is provided by the strong correlations between annualized mean growth rates of green turtles and both sea surface temperatures (SST) in the West Atlantic for years of declining growth rates (r = -.94) and the Multivariate ENSO Index (MEI) for all years (r = .74). Granger-causality analysis also supports the latter finding. We discuss multiple stressors that could reinforce and prolong the effect of the ERS. This study demonstrates the importance of region-wide collaborations.

DOI: 10.1111/gcb.13712

Cite this paper

@article{Bjorndal2017EcologicalRS, title={Ecological regime shift drives declining growth rates of sea turtles throughout the West Atlantic.}, author={Karen A Bjorndal and Alan B Bolten and Milani Y. Chaloupka and Vincent S Saba and Cl{\'a}udio Bellini and Maria Angela Marcovaldi and Armando Jos{\'e} Barsante Santos and Luis Felipe Wurdig Bortolon and Anne B. Meylan and Peter A. Meylan and Jennifer Gray and Robert Hardy and Beth Brost and Michael J. Bresette and Jonathan C. Gorham and Stephen Connett and Barbara Van Sciver Crouchley and Mike Dawson and Deborah M Hayes and Carlos E. Diez and Robert P van Dam and Sue Willis and Mabel Nava and Kristen M. Hart and Michael Cherkiss and Andrew Crowder and Clayton Pollock and Zandy M. Hillis-Starr and Fernando A Mu{\~n}oz Tener{\'i}a and Roberto L. Herrera-Pav{\'o}n and Vanessa Labrada-Martag{\'o}n and Armando Lorences and Ana Negrete-Philippe and Margaret Lamont and Allen M. Foley and Rhonda Bailey and Raymond R. Carthy and Russell A Scarpino and Erin McMichael and Jane A Provancha and Annabelle Brooks and Adriana Jardim and Milagros L{\'o}pez-Mendilaharsu and Daniel Gonz{\'a}lez-Paredes and Andr{\'e}s Estrades and Alejandro Fallabrino and Gustavo Mart{\'i}nez-Souza and Gabriela M V{\'e}lez-Rubio and Ralf H. Boulon and Jaime Agustin Collazo and Robert Wershoven and Vicente Guzm{\'a}n Hern{\'a}ndez and Thomas B. Stringell and Amdeep Sanghera and Peter B. Richardson and Annette C. Broderick and Quinton Phillips and Marta C. Calosso and John A. B. Claydon and Tasha L Metz and Amanda L Gordon and Andr{\'e} M. Landry and Donna J Shaver and Janice M. Blumenthal and Lucy Collyer and Brendan J Godley and Andrew T. B. McGowan and Matthew J Witt and Cathi L. Campbell and Cynthia J. Lagueux and Thomas L Bethel and Lory Kenyon}, journal={Global change biology}, year={2017}, volume={23 11}, pages={4556-4568} }