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Ontogenetic diet shifts of green sea turtles (Chelonia mydas) in a mid-ocean developmental habitat

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Claire M. Burgett
Claire M. Burgett
Claire M. Burgett
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Derek A Burkholder
Derek A Burkholder
Derek A Burkholder
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Kathryn Coates at Bermuda Government
Kathryn Coates
  • Bermuda Government
Virginia L. Fourqurean
Virginia L. Fourqurean
Virginia L. Fourqurean
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Abstract and Figures

Green sea turtles (Chelonia mydas) arrive on the geographically isolated Bermuda Platform as small juveniles and remain until they are approaching sexual maturity, at which point individuals depart for distant feeding and nesting sites. It has been reported that younger green turtles generally tend to carnivory or omnivory and that seagrasses become a significant food source as the turtles grow. Evidence indicates that grazing by green sea turtles in Bermuda is negatively impacting seagrass beds, thus understanding their diets is important to both conserving the turtles and their food. Stable isotope methods were used to investigate ontogenetic diet shifts of green sea turtles and to determine reliance on seagrass by larger turtles. Skin samples from 157 individual turtles and samples of known turtle foods, plants and animals, were collected for determination of consumer and food 13C and 15N values. A Bayesian stable isotope mixing model analysis indicated a wide range among individual turtles’ diets, with the greatest differences occurring between small and large turtles; larger turtles consumed seagrass almost exclusively. We also examined diet changes in 12 turtles captured in two successive years; these recapture data confirmed the changes in diet suggested by the relationship between size of turtles and diet composition. Very limited evidence was found of any diet variation among larger turtles that would indicate a shift away from declining seagrasses as their major food source.
Capture locations of turtles on the Bermuda Platform. Inset shows location of Bermuda in the western North Atlantic Ocean
Capture locations of turtles on the Bermuda Platform. Inset shows location of Bermuda in the western North Atlantic Ocean
… 
Nitrogen and carbon stable isotope ratios (in standard δ notation in ‰) for all green turtles (Chelonia mydas, n = 157) and potential food groups (macroalgae, n = 60; animals, n = 52; and seagrass, n = 455) on the Bermuda Platform. Descriptive box-and-whisker plots in the margins show the distribution of the values for each group, with median at the central line, first to third quartile in the boxes (IQR), and the whiskers indicate 1.5 × IQR. Open circles in the box-and-whiskers plots indicate data outside 1.5 × the IQR
Nitrogen and carbon stable isotope ratios (in standard δ notation in ‰) for all green turtles (Chelonia mydas, n = 157) and potential food groups (macroalgae, n = 60; animals, n = 52; and seagrass, n = 455) on the Bermuda Platform. Descriptive box-and-whisker plots in the margins show the distribution of the values for each group, with median at the central line, first to third quartile in the boxes (IQR), and the whiskers indicate 1.5 × IQR. Open circles in the box-and-whiskers plots indicate data outside 1.5 × the IQR
… 
Size distribution of the green sea turtles (Chelonia mydas) captured in 2012, given in the frequency of observations within 10 cm categories of SCL
Size distribution of the green sea turtles (Chelonia mydas) captured in 2012, given in the frequency of observations within 10 cm categories of SCL
… 
Variation in stable isotope ratios (A: δ¹³C, B: δ¹⁵N, in ‰) of skin samples as a function of size class for captured green turtles (Chelonia mydas). There were significant differences among size classes in δ¹³C [ANOVA, F (4, 152) = 35.6, P < 0.001], but no significant differences in δ¹⁵N [ANOVA, F (4, 152) = 1.6, P = 0.173]. Letters denote homogenous subsets of the data (Tukey post hoc test). N by size class: 20–30 cm = 28; 30–40 cm = 73; 40–50 cm = 29; 50–60 cm = 16; 60–70 cm = 11
Variation in stable isotope ratios (A: δ¹³C, B: δ¹⁵N, in ‰) of skin samples as a function of size class for captured green turtles (Chelonia mydas). There were significant differences among size classes in δ¹³C [ANOVA, F (4, 152) = 35.6, P < 0.001], but no significant differences in δ¹⁵N [ANOVA, F (4, 152) = 1.6, P = 0.173]. Letters denote homogenous subsets of the data (Tukey post hoc test). N by size class: 20–30 cm = 28; 30–40 cm = 73; 40–50 cm = 29; 50–60 cm = 16; 60–70 cm = 11
… 
a Absolute change in δ¹³C as a function of straight carapace length for all recaptured green turtles (Chelonia mydas) from Bermuda. b Absolute change in δ¹⁵N for as a function of straight carapace length for all recaptured turtles from Bermuda. Y-axes indicate difference in stable isotope ratios between years for each individual
+3
a Absolute change in δ¹³C as a function of straight carapace length for all recaptured green turtles (Chelonia mydas) from Bermuda. b Absolute change in δ¹⁵N for as a function of straight carapace length for all recaptured turtles from Bermuda. Y-axes indicate difference in stable isotope ratios between years for each individual
… 
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Vol.:(0123456789)
1 3
Marine Biology (2018) 165:33
https://doi.org/10.1007/s00227-018-3290-6
ORIGINAL PAPER
Ontogenetic diet shifts ofgreen sea turtles (Chelonia mydas)
inamid‑ocean developmental habitat
ClaireM.Burgett1· DerekA.Burkholder1,2 · KathrynA.Coates3· VirginiaL.Fourqurean4,5 ·
W.JudsonKenworthy6· SarahA.Manuel3· MarkE.Outerbridge3· JamesW.Fourqurean1
Received: 13 June 2017 / Accepted: 10 January 2018 / Published online: 19 January 2018
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
Green sea turtles (Chelonia mydas) arrive on the geographically isolated Bermuda platform as small juveniles and remain
until they are approaching sexual maturity, at which point individuals depart for distant feeding and nesting sites. It has been
reported that younger green turtles generally tend to carnivory or omnivory and that seagrasses become a significant food
source as the turtles grow. Evidence indicates that grazing by green sea turtles in Bermuda is negatively impacting seagrass
beds, thus understanding their diets is important to both conserving the turtles and their food. Stable isotope methods were
used to investigate ontogenetic diet shifts of green sea turtles and to determine reliance on seagrass by larger turtles. Skin
samples from 157 individual turtles and samples of known turtle foods, plants and animals, were collected for determination
of consumer and food δ13C and δ15N values. A Bayesian stable isotope mixing model analysis indicated a wide range among
individual turtles’ diets, with the greatest differences occurring between small and large turtles; larger turtles consumed
seagrass almost exclusively. We also examined diet changes in 12 turtles captured in two successive years; these recapture
data confirmed the changes in diet suggested by the relationship between size of turtles and diet composition. Very limited
evidence was found of any diet variation among larger turtles that would indicate a shift away from declining seagrasses as
their major food source.
Introduction
Through their lives animals may experience profound
changes in ecology and biology, among these are fundamen-
tal changes in food sources and choices. Ontogenetic shifts
in diet are a common feature of the life history of a diverse
group of organisms, ranging from arthropods to vertebrates
(Werner and Gilliam 1984). Such shifts are frequently cou-
pled with changes in size and habitat. Ontogenetic shifts
from carnivorous and omnivorous juveniles to herbivorous
adults are common in reptiles, including green sea turtles
(Werner and Gilliam 1984; Polis etal. 1996). Stable isotope
diet studies have shown such a shift from a macroalgal and
animal-based diet in the pelagic environment of very young
green turtles to a plant-based diet after the juvenile turtles
move into neritic habitats (e.g., Reich etal. 2007; Arthur
etal. 2008; Howell etal. 2016).
The availability, quality and kinds of food in different
environments may vary widely, and animals must have
behaviors that ensure survival across all the conditions
encountered in their lifetime. Many marine organisms with
ontogenetic diet shifts have larvae and juveniles that feed
Responsible Editor: L. Avens.
Reviewed by Undisclosed experts.
Electronic supplementary material The online version of this
article (http s://doi.org/10.1007 /s002 27-018-3290 -6) contains
supplementary material, which is available to authorized users.
* James W. Fourqurean
jim.fourqurean@fiu.edu
1 Department ofBiological Sciences, Marine Education
andResearch Center, Florida International University,
OE148, 11200 SW 8th St, Miami, FL33199, USA
2 Present Address: Halmos College ofNatural Sciences
andOceanography, Nova Southeastern University, 8000
North Ocean Drive, DaniaBeach, FL33004, USA
3 Department ofEnvironment andNatural Resources, Bermuda
Ministry oftheEnvironment, HamiltonParishFL04,
Bermuda
4 Miami Palmetto Senior High School, 7460 SW 118th St,
Pinecrest, FL33156, USA
5 Present Address: Marine Education andResearch Center,
Florida International University, OE148, 11200 SW 8th St,
Miami, FL33199, USA
6 109 Holly Lane, Beaufort, NC28516, USA
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... SIA is a powerful tool for assessing diet and trophic ecology (Haywood et al., 2019). It has been used to infer site fidelity and identify newly recruited animals (Vélez-Rubio et al., 2016;Piovano et al., 2020); estimate the relative importance of different dietary items (Piovano et al., 2020;Gama et al., 2021;Reynolds et al., 2023); identify changes in diet with the size of individuals (Shimada et al., 2014;Vélez-Rubio et al., 2016;Burgett et al., 2018); and quantify the isotopic niche that species occupy (Newsome et al., 2007;Weber et al., 2023). ...
... At each station, prey items were collected within a 20-m radius of an anchored boat and were kept on ice. In the lab, samples were rinsed and sand/epibiota removed with a razor blade (Burkholder et al., 2011;Burgett et al., 2018). Vegetation items were dried in a drying oven at 60 • C until dry and stored in aluminum foil packets. ...
... We found isotopic differences between small and large green turtles, with the δ 15 N becoming more depleted with age. Green turtles, especially in warmer waters, have flexible ontogenetic shifts, from a mostly carnivorous, oceanic juvenile stage to a neritic juvenile stage, shifting to a plant-dominated diet in adulthood (Howell et al., 2016;Burgett et al., 2018); however, diet can vary by region/temperature . In north-western Australia, seagrass was found important for all sizes, with macroalgae possibly being important to smaller sized green turtles, and jellyfish increased in diet with size (Vanderklift et al., 2023). ...
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... By comparison, Arthur et al. (2008) determined that recruitment does not occur until 5−10 yr at roughly a 44 cm curved carapace length (CCL) in areas of the southwest Pacific. In Caribbean waters, recruitment into neritic zones of less than 50 m depths entails an ontogenetic shift in feeding strategies from an omnivorous diet to a predominantly herbivorous diet of seagrass and macroalgae (Bolten et al. 2003, Reich et al. 2007, Arthur et al. 2008, Howell et al. 2016, Burgett et al. 2018, Hancock et al. 2018). This ontogenetic shift was once thought to be perma-nent; however, several studies have shown that the shift may be facultative or compensatory to meet the growth needs of an individual when nutrients are low (Hatase et al. 2006) or even intermediary as juveniles slowly transition from their pelagic phase (Cardona et al. 2009, Vander Zanden et al. 2013a). ...
... Hawksbills are also thought to make an ontogenetic shift in feeding as they recruit from oceanic waters to neritic zones (Howell et al. 2016, Burgett et al. 2018, Ferreira et al. 2018. Musick & Limpus (1997) reported that hawksbill recruitment into developmental habitats in the Virgin Islands occurred at a smaller size than either loggerheads Caretta caretta or green turtles and is generally accepted to occur at a carapace length of 20−30 cm (NMFS & USFWS 1998, Bolten et al. 2003. ...
... In developmental habitats where juvenile hawksbills and green turtles have recently recruited into neritic zones, we expect to see a degree of overlap in prey selection between these species . As the juveniles mature, we would expect to see a divergence in foraging strategies between species after ontogeny, with hawksbills trending toward carnivory and green turtles trending toward an herbivorous diet of seagrasses (Reich et al. 2007, Arthur et al. 2008, Howell et al. 2016, Burgett et al. 2018. Studies in the Bahamas indicate that green turtles approach a seagrass-dominated diet roughly 7 yr after recruitment (Burgett et al. 2018), and juveniles have been estimated to stay in developmental habitats for up to 20 yr (Turner Tomaszewicz et al. 2015). ...
Hawksbill and green turtle niche overlap in a marine protected area, U.S. Virgin Islands
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  • Nov 2023
Studying how species interact with their environment and other co-occurring species are 2 main aspects of ecology. For marine turtles, ocean currents drive migratory routes and may determine the location of surrounding foraging grounds. As a result, circumglobal species like the hawksbill turtle Eretmochelys imbricata and green turtle Chelonia mydas adapt to diverse foraging habitats and employ varied feeding strategies. Dietary specializations may reduce competition for available food and space resources between co-occurring hawksbill and green turtles in US Virgin Island shallow reef habitats. This study analyzed isotopic data from immature hawksbill (n = 49; range: 18.7-49.8 cm straight carapace length [SCL]) and green turtles (n = 225; range: 24.1-69.4 cm SCL) to examine foraging niche. We used nitrogen stable isotope (δ ¹⁵ N) values as an indicator of trophic positioning and carbon stable isotope (δ ¹³ C) values as a habitat variable. Turtles were hand-captured across an 8 yr period (2012-2019), which facilitated the distinction of isotopic patterns in both the environment and among individual turtles. Understanding variations in habitat, community dynamics, and dietary consumption allowed us to utilize a 5 point framework to translate isotopic space to foraging niche. We found that the site’s relatively stable environmental conditions allow for isotopic overlap between hawksbill and green turtles despite the specialized feeding strategies each species employs. We also underscore the need to evaluate species-specific tissue turnover estimates as evidenced by the influence of tropical storms on recaptured turtle isotopic signatures. These findings inform our understanding of resource use for these imperiled species at our study site and are useful for future global isotopic comparisons.
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... Conventional information assumes that green turtles have an oceanic stage early in life and usually flip to neritic, more coastal habitats after they attain an age of between 3 and 10 years (Chaloupka et al., 2004;Reich et al. 2007) which corresponds to a carapace length varying from 25 to 44 cm (Arthur et al. 2008;Boyle and Limpus, 2008). The onset of dietary changes, according to Vélez-Rubio et al. (2016) and Burgett et al. (2018), begins around 40 to 45 cm of carapace length when neustonic invertebrates are substitute by macrophytes as the main diet item (Reich et al. 2008). However, the timing of the ontogenetic dietary shift and the degree of omnivory may vary. ...
Regional differences in Hg contents in the liver and muscle of the green turtle (Chelonia mydas) from three foraging grounds in Northeast Brazil
Article
Full-text available
  • Dec 2023
  • ENVIRON SCI POLLUT R
Mercury (Hg) is a highly toxic pollutant that endangers several marine animals, including green sea turtles (Chelonia mydas), particularly in their foraging grounds along Brazilian coastal waters. Environmental Hg levels differ along this extensive littoral, rendering mandatory Hg long-term assessments of the different Hg fate in different sectors of the Brazilian coast. This study quantifies total Hg concentrations in the liver and muscle of green sea turtle populations from three foraging coastal regions in northeastern Brazil and analyzes Hg concentration differences given the locality and size of 61 juvenile individuals sampled. The results showed wide variations in Hg concentrations in the liver (81–3135 ng g−1) and muscle (10.1–8569 ng g−1). There was no significant correlation between animal size and Hg concentrations. Also, no difference was found among areas, reflecting the opportunistic feeding habit of juveniles of this species. This suggests that, in the case of green turtles, the ontogenetic change of diet plays an important role in influencing Hg concentrations found in this species.
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... Prey resources and particulate organic matter (POM) were collected throughout St. Joseph Bay to inform a Bayesian mixing model(McClellan et al. 2010;Witteveen and Wynne 2016;Burgett et al. 2018) (Fig. 1). Particulate organic matter ...
Isotopic niche partitioning in a multi-species assemblage
Article
Full-text available
  • Nov 2023
  • MAR BIOL
Multi-species assemblages can help identify key resources in their habitat by evaluating how they are partitioning their resources. Here we used the isotopic niche of loggerhead, Kemp’s ridley, and green sea turtles to assess their ecological niche within a Gulf of Mexico bay. Additionally, we assessed temporal and size-class variation in their diets by comparing the δ¹³C and δ¹⁵N values over various capture years and size classes. Based on the isotopic niche overlap results, interspecific competition occurs among loggerhead, Kemp’s ridley, and smaller green turtles. Green turtle and Kemp’s ridley diet varied by size class, while Kemp’s ridley diet also varied temporally. The three species partition resources by selecting different preferred diet items, although some overlap in diet, including between the herbivorous (green) and carnivorous (Kemp’s ridley, loggerhead) species, appears to occur. The high quality of this habitat may allow species co-existence and population recovery despite the possible use of shared resources.
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... Green turtles display an ontogenetic shift in diet toward herbivory at sizes greater than 30 cm CCL in benthic habitats (Burgett et al., 2018) and have a predominantly seagrass-based diet in the Western Indian Ocean (Stokes et al., 2019). For example, juvenile green turtles forage on animal matter in coastal habitats of southern Peru and then transition from a high-to low-calorie diet when they migrate north to feed on abundant vegetation (Quiñones et al., 2022). ...
Synergistic use of UAV surveys, satellite tracking data, and mark-recapture to estimate abundance of elusive species
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  • Mar 2023
Estimating population abundance is central to many ecological studies and important in conservation planning. Yet the elusive nature of many species makes estimating their abundance challenging. Abundance estimates of sea turtles , marine birds, and seals are usually made when breeding adults are ashore, while life stages spent at sea, including as juveniles, are often poorly sampled. We used a combination of high-resolution satellite tracking (Fastloc-GPS), uncrewed aerial vehicle (UAV) surveys, and capture-mark-recapture approaches to assess the abundance of immature hawksbill (Eretmochelys imbricata) and green turtles (Chelonia mydas) in a tidal lagoon of the Chagos Archipelago (Indian Ocean). We captured, marked, and released 50 turtles (48 hawksbill and 2 green turtles) prior to UAV surveys and used satellite tracking data from 27 immature turtles (25 hawksbill and 2 green turtles) to refine the estimated numbers of marked turtles available for resighting and those likely to have emigrated from the study area. We estimated a total of 339 turtles in the lagoon with a density variation at different tidal heights between 265 turtles km −2 at high water and 499 turtles km −2 at low water. Of these, 91% were hawksbills and 9% were green turtles. These hawksbill densities are the highest reported among 17 foraging sites recorded around the world and likely reflect successful long-term protection of turtles in the Chagos Archipelago.
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Ontogenetic changes in green turtle (Chelonia mydas) diet and home range in a tropical lagoon
Article
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  • Aug 2023
Ontogenetic changes in habitat and diet are widespread among marine species. Most species of sea turtles are characterized by extreme ontogenetic changes in habitat use and diet, with large changes occurring in early developmental stages (e.g., neonates to juveniles). Changes can continue even after recruitment to shallow coastal habitats. In places where substantial transitions in habitat occur across short distances, it is possible that the distances of developmental movements from one habitat to another could be short. We investigated ontogenetic changes in home range size, home range location and diet of Chelonia mydas in a tropical coastal lagoon in north-western Australia by combining acoustic telemetry with stable isotope analysis. There was a substantial (but nonlinear) increase in home-range size (kernel utilization distribution: KUD) with length, and an increase in the average distance of the center of home ranges from shore with length: larger turtles tended to occupy larger areas further from the shore. These patterns were accompanied by complex nonlinear changes in δ¹³C, δ¹⁵N and δ³⁴S of red blood cells and nails; changes were rapid from 36 cm (the length of the smallest individual captured) to 50 cm, before reversing more gradually with increasing size. δ¹⁵N and δ³⁴S (but not δ¹³C) of red blood cells and nails increased monotonically with KUD and distance from shore. Seagrass was likely an important food for all sizes, macroalgae was potentially important for small (< 60 cm CCL) individuals, and the proportion of scyphozoan jellyfish in diet increased monotonically with size. The combination of acoustic telemetry and stable isotope analysis revealed ontogenetic shifts in use of space and diet across short distances in a tropical coastal lagoon.
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Adipose tissue estimation of foraging and nesting green turtles Chelonia mydas using bioelectrical impedance analysis
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  • Jun 2023
Adipose tissue is the main energy store in sea turtles and fluctuates in response to dietary conditions and external stressors. Monitoring programmes commonly use body condition indices (BCIs) to infer the nutritional and health status of sea turtle populations. However, BCIs have poor predictive power for estimating adipose tissue. We introduce the use of bioelectrical impedance analysis (BIA) as a portable technique to estimate adipose tissue in green turtles Chelonia mydas . The aims of this study were to estimate adipose tissue of green turtles on the Great Barrier Reef (Australia), and to examine whether adipose tissue is a more sensitive indicator than BCI. Turtles (n = 250) were sampled at 3 foraging sites and at a nesting beach with differing levels of anthropogenic impact. Differences in adipose tissue, Fulton’s BCI, and body mass across study sites and life stages were assessed by conducting linear mixed effects models. BIA estimates of mean adipose tissue revealed significant differences across life stages and sampling sites, that were not found using BCI data. Mean adipose tissue was estimated to be 4.6 ± 0.6% (% body mass ± SD) and was not correlated with mean BCI (1.2 ± 0.1). Adipose tissue was not reduced in turtles foraging at sites with a high level of anthropogenic impact. Adult turtles had significantly higher adipose tissue values than juveniles and subadults. Adult females measured during and shortly before nesting season had the highest adipose tissue values (%). BIA is a practical method for estimating adipose tissue, and we recommend this technique for consideration in sea turtle monitoring programmes.
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Long-term and seasonal patterns of sea turtle home ranges in warm coastal foraging habitats: Implications for conservation
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Ontogenetic shifts in diet and habitat of juvenile green sea turtles in the northwestern Gulf of Mexico
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Effective management of a rapidly increasing juvenile green sea turtle Cheloni mydas population necessitates an understanding of the foraging grounds utilized throughou ontogeny. We used stomach content (SCA) and stable isotope analyses (SIA) of multiple siz classes of green turtles foraging along the middle (MTC) and lower Texas coasts (LTC) in th northwestern Gulf of Mexico to identify ontogenetic shifts in foraging behavior. Spatial difference in diet and habitat residency were examined based on samples gathered from live (n = 55 and deceased turtles (n = 114). Additionally, the isotopic composition of putative forage materia within nearshore and inshore habitats was investigated to determine prey contribution to diet Green turtle recruitment to neritic channel environments in Texas waters at sizes 25 cm straigh carapace length (SCL) was established based on the presence of benthic macroalgae in the diet Integration of SCA with SIA of carbon and nitrogen in scute material, as well as potential prey revealed a subsequent inshore shift to seagrass beds before obtaining 35 cm SCL for turtles of th LTC, while turtles from the MTC exhibited considerable variation in size at transition. This stud improves our understanding of the feeding ecology of green turtles within critical foragin grounds along the Texas coast.
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Water quality, isoscapes and stoichioscapes of seagrasses indicate general P limitation and unique N cycling in shallow water benthos of Bermuda
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  • BG
Striking spatial patterns in stable isotope ratios (isoscapes) and elemental ratios (stoichioscapes) of seagrass leaves and the water column nutrients indicate general P limitation of both water column and benthic primary productivity on the Bermuda Platform, and they highlight the role of the Bermuda Islands as a source of N and P. We found consistent differences among the four seagrass species (Syringodium filiforme, Thalassia testudinum, Halodule sp. and Halophila decipiens) in the N, P, d13C and d15N of leaf tissues. The d15N of seagrass leaves was especially variable, with values from -10.1 to 8.8 ‰, greatly expanding the reported range of values for all seagrass species globally. Spatial patterns from both the water column and the seagrass leaves indicated that P availability was higher near shore, and d15N values suggest this was likely a result of human waste disposal. Spatially contiguous areas of extremely depleted seagrass 15N suggest unique N sources and cycling compared to other seagrass-dominated environments. Seagrass N: P values were not as far from the stoichiometric balance between N and P availability as in the water column, and there were no strong relationships between the water column N: P and the seagrass N: P. Such isoscapes and stoichioscapes provide valuable ecogeochemical tools to infer ecosystem processes as well as provide information that can inform food web and animal movement studies.
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Increased use of non-native algae species in the diet of the Green Turtle (Chelonia mydas) in a primary pasture ecosystem in Hawaii
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The Green Turtle, Chelonia mydas, has modified its feeding behavior over the past 36 years to include the increasing abundance of non-native algae growing in the greater Kaneohe Bay area of Oahu, Hawaii. Changes in diet of the Turtles are correlated with an increase in abundance of non-native algae. Turtles are eating 135 species of marine vegetation including the following seven non-native species: Acanthophora spicifera, Hypnea musciformis, Gracilaria salicornia, Eucheuma denticulatum, Gracilaria tikvahiae, Kappaphycus striatum and Kappaphycus alvarezii. Non-native algae now represent 0.64 proportion of the Turtle diet. The present study for the additional 8 years 2005–2012, shows the utilization of non-native species for food has increased 24% since the last study that included 28 years 1976–2005. Average time for the Turtles to make the shift to non-native species is 10–12 years for the more invasive species and 20–30 years for the slower growing species. During this same time period the numbers of C. mydas, body size, and growth rates have also increased, partly due to the increased abundance of the additional non-native food items. This study verifies that the trend of Turtles eating higher amounts of non-native algae in Kaneohe Bay is now stronger than first reported in 2009.
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Regional and local factors determining green turtle Chelonia mydas foraging relationship with the environment
Article
  • Jun 2015
Changes in green turtle Chelonia mydas foraging patterns were evaluated within a latitudinal gradient along tropical and subtropical coasts in the southwestern Atlantic and investigated as to how green turtles responded to regional and local changes in their foraging habitats. In addition, we evaluated how changes in feeding ecology caused populations to be more susceptible to various anthropogenic threats. The literature and original diet data of 427 green turtles were analyzed. Turtles from tropical and subtropical reefs exhibited the classic pattern of herbivorous benthic foraging, turtles from estuarine areas exhibited a more generalist diet and pelagic foraging, and turtles from colder reef areas, located between the winter isotherms of 10°C and 20°C, exhibited an omnivorous diet and pelagic foraging strategy. The amount of ingested animal matter was higher in occurrence and abundance in the green turtle diets in the most southern foraging areas. Foraging ecology was influenced by regional (phycogeographical provinces and water temperature) and local (urbanization and rivers) factors. Green turtles exhibited high foraging plasticity, and their importance to the ecosystem was not restricted to their role as herbivores. Green turtles may also have an important role as second-order consumers in certain areas, mainly in the cooler waters at the extremes of their distribution. Foraging plasticity was observed both in the type of diet item and foraging strategy, which implies that there may be variation in the exposure of populations to threats.
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Movements and Feeding Ecology of Immature Green Turtles (Chelonia mydas) in a Florida Lagoon
Article
  • Dec 1983
  • COPEIA
The seasonal and diel movements of 14 green turtles (Chelonia mydas) in Mosquito Lagoon, Florida were monitored using sonic telemetry. The feeding ecology of this population was also studied using dissection and stomach flushing techniques. Immature green turtles made random, long distance movements (x̄ = 8.2 km/day) and occupied deeper waters (x̄ = 1.6 m), apparently not feeding, when water temperatures ranged from 11-18 C; at water temperatures above 25 C they adopted a home range. Turtles were active at temperatures up to 34 C. No diel pattern was evident during winter months, but a definite bimodal pattern was evident at high water temperatures, with green turtles feeding on grass flats in midmorning and midafternoon and moving into deeper waters during the midday hours. Home range area was significantly correlated with body weight but the center of grazing activity was not. Seagrasses made up 88% of the turtles' diet throughout the year.
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Nutritional Ecology of Sea Turtles
Article
  • Aug 1985
  • COPEIA
Analysis of the nutritional ecology of sea turtles, that is, how nutrition influences their biology and determines their interactions with the environment, is necessarily restricted to the green turtle, Chelonia mydas. Our knowledge of the nutrition of the other species of sea turtles is limited to information on diet from gut content studies and a few reports on the anatomy and histology of the digestive tract. The literature on diet and gut anatomy and histology are summarized in the first two sections of this review. The remainder of this review is a discussion of the nutrition of Caribbean green turtles; their digestive efficiencies, adaptations to their major food plant Thalassia testudinum, and the effect the diet has, through nutrient limitation, on their productivity. Although Thalassia is a very abundant food source which is fairly constant in productivity and nutrient quality, few herbivores graze on it. Green turtles have two adaptations that enable them to utilize Thalassia more efficiently. First, they maintain grazing plots where, by cropping the young regrowth, they obtain blades of much higher quality because of lower lignin and higher nitrogen concentrations. Secondly, they have a hindgut microbial fermentation that digests the fiber in Thalassia and yields both an important energy source to the green turtle, in the form of volatile fatty acids, and gives the green turtle access to the highly digestible cell contents. In spite of the advantages of these adaptations-grazing plots and hindgut fermentation-they are not sufficient to prevent nutrient limitation and the resulting slow growth rates, delayed sexual maturity, and reduced reproductive output. Comparison with green turtles on high-quality, pelleted diets shows that the productivity of wild populations is well below their genetic potential. Ironically, nutrient limitation acting through delayed sexual maturity may benefit green turtles during periods of intense exploitation by man.
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