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.

Contrasted habitats and individual plasticity drive the fine scale movements of juvenile green turtles in coastal ecosystems

“…Although similarities in terms of movements were observed between the five foraging grounds, it is also worth mentioning the strong inter-site and inter-individual variability. The high degree of plasticity in sea turtles' movements and home ranges has already been recorded in numerous studies [17,89,[92][93][94], but this is the first time such plasticity has been demonstrated by a metaanalysis of juvenile green turtles' movements tracked from five contrasted sites from the same Regional Management Unit [95]. Inter-individual variability could be attributed to both intrinsic (e.g.…”

Staat van de natuur van Caribisch Nederland 2017 : een eerste beoordeling van de staat (van instandhouding), bedreigingen en managementimplicaties van habitats en soorten in Caribisch Nederland

“…De eilanden lijken ook in belangrijkheid snel toe te voor de functie als foerageergebied Bjorndal, 2017). Het gebied van Lac-baai blijkt zelfs een van de beste foerageergebieden te zijn voor de Soepschildpad, alwaar deze soort de hoogste groeisnelheden van de gehele Caribische regio vertoont (Bjorndal et al, 2017 Esteban et al, 2015).…”

“…Het gebied van Lac-baai blijkt zelfs een van de beste foerageergebieden te zijn voor de Soepschildpad, alwaar deze soort de hoogste groeisnelheden van de gehele Caribische regio vertoont (Bjorndal et al, 2017 Esteban et al, 2015). Het leggen en uitkomen van nesten vindt hoofdzakelijk plaats van april-oktober.…”

Evaluating viability of sea turtle foraging populations at high latitudes: age and growth of juveniles along the French Atlantic coast

“…These genetic data suggest that juvenile green sea turtle occurrence in the Bay of Biscay likely results from a combination of Gulf Stream/North Atlantic Current transport and stochastic storm events, similar to loggerheads (Monzón-Argüello et al 2012). Correspondingly, green sea turtle age and growth data generated by the current analyses were compared with those from juvenile foraging populations along the US Atlantic and Gulf coasts and western South Atlantic (Zug & Glor 1998, Goshe et al 2010, Avens et al 2012, Bjorndal et al 2017, Lenz et al 2017, thought to originate from some of the same source populations (Bass & Witzell 2000, Bass et al 2006.…”