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

Abstract

Background: A strong behavioural plasticity is commonly evidenced in the movements of marine megafauna species, and it might be related to an adaptation to local conditions of the habitat. One way to investigate such behavioural plasticity is to satellite track a large number of individuals from contrasting foraging grounds, but despite recent advances in satellite telemetry techniques, such studies are still very limited in sea turtles.Methods: From 2010 to 2018, 49 juvenile green turtles were satellite tracked from five contrasting feeding grounds located in the South-West Indian Ocean in order to (1) assess the diel patterns in their movements, (2) investigate the inter-individual and inter-site variability, and (3) explore the drivers of their daily movements using both static (habitat type and bathymetry) and dynamic variables (daily and tidal cycles). Results: Despite similarities observed in four feeding grounds (a diel pattern with a decreased distance to shore and smaller home ranges at night), contrasted habitats (e.g. mangrove, reef flat, fore-reef, terrace) associated with different resources (coral, seagrass, algae) were used in each island. Conclusions: Juvenile green turtles in the South-West Indian Ocean show different responses to contrasting environmental conditions -both natural (habitat type and tidal cycle) and anthropogenic (urbanised vs. uninhabited island) demonstrating the ability to adapt to modification of habitat.

Space use and relative habitat selection for immature green turtles within a Caribbean marine protected area

“…Prior studies have reported similar home range sizes, with the estimated home ranges for immature green turtles in Hawaii being < 3 km 2 [54] and in Florida were 3 km 2 [42]. Further, turtle core use areas, defined by 50% KDEs, within BIRNM were small (0.3 ± 0.0 km 2 ), similar to that reported by Makowski et al [42] (0.5 ± 0.4 km 2 ) and Chambault et al [55] (0.2 ± 0.3 km 2 ). When resource distributions (i.e., food and shelter) were tightly clustered, space use for immature green turtles was constrained [42,47,54].…”

“…Turtle MCPs and KDEs demonstrated space use was largely located directly south of the island and to the east and west, thus, space use did not perfectly match the predicted relative selection probabilities that were observed across a much broader spatial extent. This may be due to tagging effort being generally located south of the island where green turtle abundances were highest, thus, if immature green turtles exhibit small home ranges as demonstrated here and by Brill et al [54], Makowski et al [42], Griffin et al [47], and Chambault et al [55], we would expect tagged individuals to remain near their capture locations. Further, the RSF model could have been improved with additional covariates that capture additional environmental characteristics (e.g., fetch, wave energy, seagrass total area), ecological processes (e.g., density dependence, predator landscape metrics, [57]), and green turtle foraging strategies.…”

High fidelity of sea turtles to their foraging grounds revealed by satellite tracking and capture-mark-recapture: New insights for the establishment of key marine conservation areas

“…Once corrected to take the location measurement errors into account, the HR and CA sizes in Martinique are smaller than those found for immature green turtles in Florida (HR: 154 ± 136 km 2 , CA: 22 ± 22 km 2 ; Hart and Fujisaki, 2010), and in North Carolina (HR: 85 ± 48 km 2 ; McClellan and Read, 2009) with Argos-based locations, but consistent with those found for immature and adult green turtles in the Indian Ocean, using Fastloc-GPS data (Chambault et al, 2020;Christiansen et al, 2017).…”

“…Two turtles settled in the bay of Fort-de-France, which provides algae and seagrass and is fringed by a mangrove. Mangrove compounds have been regularly found in mouth and gut contents of green turtles, and juveniles have already been reported inhabiting mangroves (Chambault et al, 2020;Guebert-Bartholo et al, 2011). A few Martinican turtles may feed in this habitat, in relation with specific physiological adaptations (to digest fruits, algae, and highly energetic animal prey; Bjorndal et al, 2000).…”

“…Other factors such as body condition in relation to predation risk (review by Hays, 2008), intraspecific competition (Svanbäck and Bolnick, 2005), or behavioural plasticity (Chambault et al, 2020) may drive individuals to settle in various, including seldom-used, habitats. Site selection has been demonstrated to potentially affect size-specific growth rates, with individuals growing slowly moving from lower to higher quality habitats (Bjorndal et al, 2000).…”