Diel and seasonal patterns in activity and home range size of green turtles on their foraging grounds revealed by extended Fastloc-GPS tracking

Christiansen, Fredrik; Esteban, Nicole; Mortimer, Jeanne A.; Dujon, Antoine; Hays, Graeme C.

doi:10.1007/s00227-016-3048-y

Cited by 70 publications

(81 citation statements)

References 80 publications

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“…Seagrass samples taken only hundreds of metres apart can have as great a difference in δ 34 S as samples taken thousands of kilometres apart . Nevertheless, such variation over small geographic scales is incorporated within large megavertebrates, such as green turtles, that forage over tens of square kilometres (Broderick et al 2007, Christiansen et al 2017, and the diet assimilated provided distinct differences among distant foraging areas. In a similar study, Tucker et al (2014) did not find δ 34 S in loggerhead turtles Caretta caretta to be informative because the intra-foraging site variation in δ 34 S values encompassed a much greater range (11 to 15 ‰ at several sites), effectively masking among-site differences.…”

Section: Selecting the Elements For Stable Isotope Analysismentioning

confidence: 99%

Satellite tracking and stable isotope analysis highlight differential recruitment among foraging areas in green turtles

Bradshaw¹,

Broderick²,

Carreras³

et al. 2017

Mar. Ecol. Prog. Ser.

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Identifying links between breeding and non-breeding sites in migratory animals is an important step in understanding their ecology. Recognising the relative importance of foraging areas and ascertaining site-specific levels of recruitment can provide fundamental and applied insights. Here, satellite telemetry and the stable isotope ratios (δ 13 C, δ 15 N and δ 34 S) of 230 green turtles Chelonia mydas from a regionally important rookery in northern Cyprus were employed to evaluate the relative importance of 4 foraging areas. A preliminary analysis of stable isotope ratios suggested that a major foraging area had been missed through satellite telemetry as a large proportion of turtles had isotope ratios that did not correspond to sites previously identified. Stable isotope ratios were then employed to select 5 turtles to be fitted with platform terminal transmitters in 2015. All 5 turtles were subsequently tracked to the same location, Lake Bardawil in Egypt. Serially collected tissue samples from 45 females, ranging over 2 to 4 breeding seasons, suggested that foraging site fidelity was very common, with 82% of females exhibiting extremely high temporal consistency in isotope ratios. Quantifying fidelity allowed an evaluation of foraging areaspecific contributions to each breeding cohort over the past 2 decades and demonstrated that recruitment was unequal among sites, and dynamic over time, with Egypt now currently the major contributor to the nesting aggregation. This work demonstrates the utility of stable isotope analysis to elucidate the spatial ecology of cryptic taxa and illustrates how more robust baselines can be assembled against which to measure the success of future marine conservation initiatives.

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Section: Selecting the Elements For Stable Isotope Analysismentioning

confidence: 99%

Satellite tracking and stable isotope analysis highlight differential recruitment among foraging areas in green turtles

Bradshaw¹,

Broderick²,

Carreras³

et al. 2017

Mar. Ecol. Prog. Ser.

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“…heavily used areas) within a home range (trajectory Type 2) has been documented for a range of terrestrial and marine species and has often been linked to changes in food quality and/or availability (e.g. large herbivores, Searle et al 2005; sea turtles, Christiansen et al 2017;whales, Dalla Rosa et al 2008). Animals often leave a patch before completely depleting it, usually when its quality drops below the average quality of the whole site (Charnov 1976, Searle et al 2005.…”

Section: Ontogenetic Variations Of Home Rangementioning

confidence: 99%

A groundwater-fed coastal inlet as habitat for the Caribbean queen conch Lobatus gigas—an acoustic telemetry and space use analysis

Dujon¹

2017

Mar. Ecol. Prog. Ser.

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The queen conch Lobatus (Strombus) gigas, a marine snail, is among the most important fisheries resources of the Caribbean region. To provide effective protection in marine reserves, a good understanding of its habitat usage is essential. Queen conches commonly inhabit marine habitats. In this study, its activity space in a marginal estuarine-like habitat, the groundwater-fed inlet of Xel-Há (Mexico) was determined using high-resolution acoustic telemetry (VEMCO Positioning System). Thirty-eight animals with syphonal lengths ranging from 80 to 200 mm were tagged, 1 of them with an accelerometer tag. Their trajectories were recorded for 20 mo at 5 m resolution in a closely spaced array of 12 receivers. Space-time kernel home ranges ranged from 1000 to 18 500 m 2 with an ontogenetically increasing trend. Juveniles, subadults and most adults displayed continuous, non-patchy home ranges consistent with the typical intensive feeding activity by this fast-growing gastropod. In some adults, Lévy flight-like fragmentation of home ranges was observed that may be related to feeding range expansion or other ecological drivers such as the breeding cycle. The observed small home ranges indicate that the space use of queen conch in this estuarine-like habitat is not conditioned by food availability, and despite environmental stress due to daily low-oxygen conditions, space use is comparable to that observed in more typical marine habitats. In a marine reserve context, the groundwater-fed inlet provides adequate protection of this inshore queen conch population. Such marginal habitats may play an increasingly important role in conservation management as pressure on populations increase.

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“…We used Fastloc‐GPS locations derived from four to nine satellites. Prior to the data analysis, we plotted all locations to visually identify outlying data points representing likely erroneous locations (e.g., located on land) and we followed previously established standard methods to exclude likely erroneous Fastloc‐GPS locations using the following steps (Christiansen, Esteban, Mortimer, Dujon, & Hays, ; Dujon, Lindstrom, & Hays, ; Hays et al, ; Luschi, Hays, DelSeppia, Marsh, & Papi, ; Thomson et al, ). Firstly, we excluded all locations with a residual ≥35 and we assessed if locations were biologically feasible based upon known green turtle swimming speeds (no more than 200 km/day assuming 24 hr travel (Dujon et al, ).…”

Section: Methodsmentioning

confidence: 99%

Megaherbivores may impact expansion of invasive seagrass in the Caribbean

et al. 2018

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Abstract1. Our knowledge of the functional role of large herbivores is rapidly expanding, and the impact of grazing on species coexistence and nonnative species expansion has been studied across ecosystems. However, experimental data on large grazer impacts on plant invasion in aquatic ecosystems are lacking.2. Since its introduction in 2002, the seagrass species Halophila stipulacea has rapidly expanded across the Eastern Caribbean, forming dense meadows in green turtle (Chelonia mydas)-foraging areas. We investigate the changes in seagrass species coexistence and the impacts of leaf grazing by green turtles on nonnative seagrass expansion in Lac Bay (Bonaire, Caribbean Netherlands).3. Green turtle grazing behaviour changed after the introduction of nonnative seagrass to Lac Bay in 2010. Field observations, together with time-lapse satellite images over the last four decades, showed initiation of new grazing patches (65 ha, an increase of 72%). The sharp border between grazed and ungrazed seagrass patches moved in the direction of shallower areas with native seagrass species that had previously been ungrazed. Green turtles deployed withFastloc-GPS transmitters confirmed high site fidelity to these newly cropped patches. In addition, cafeteria experiments indicated selective grazing by green turtles on native species. These native seagrass species had significantly higher nutritional values compared to the nonnative species. In parallel, exclosure experiments showed that nonnative seagrass expanded more rapidly in grazed canopies | INTRODUC TI ONLarge herbivores, whether aquatic or terrestrial, can have strong impacts on associated species and can be critical ecosystem engineers as they alter plant productivity, modify geomorphology, and influence nutrient cycling, habitat structure and plant coexistence (Bakker et al., 2016;Poore et al., 2012;Wood, Armstron, & Richards, 1967). Megaherbivores can impact plant species coexistence and species composition via multiple mechanisms. Preferential grazing on dominant plant species can promote species diversity by releasing competitors (Olff & Ritchie, 1998), or reduce diversity by selectively removing nondominant species (Hidding, Bakker, et al., 2010).Grazing can also precipitate species shift from long-lived, slow growing species, to faster growing pioneer species that are better adapted to grazing (Kelkar, Arthur, Marba, & Alcoverro, 2013;Knapp et al., 1999). Additionally, grazing on below-ground plant parts can enhance species diversity by creating regeneration niches through sediment disturbance (Hidding, Nolet, Boer, Vries, & Klaassen, 2010).The impact of herbivory on plant coexistence has been shown across diverse ecosystems, including examples from terrestrial and aquatic systems (Augustine & McNaughton, 1998;Bakker, Pagès, Arthur, & Alcoverro, 2015). This being the case, there is a potential for grazers to increase the success of invasive plants. Evidence of interactions between grazing and invasive plants go both ways.Nonnative species may come to dominate ...

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Diel and seasonal patterns in activity and home range size of green turtles on their foraging grounds revealed by extended Fastloc-GPS tracking

Cited by 70 publications

References 80 publications

Satellite tracking and stable isotope analysis highlight differential recruitment among foraging areas in green turtles

Satellite tracking and stable isotope analysis highlight differential recruitment among foraging areas in green turtles

A groundwater-fed coastal inlet as habitat for the Caribbean queen conch Lobatus gigas—an acoustic telemetry and space use analysis

Megaherbivores may impact expansion of invasive seagrass in the Caribbean

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