For the endangered green turtle, Chelonia mydas, a fundamental component of recovery and conservation is an understanding of its foraging ecology. Foraging optimality models suggest animals will select resources of high quality over those of low quality. For green turtles, this behavior is important, as sufficient quantities of nutritionally adequate forage items are necessary for growth and reproduction. One intrinsic element in the understanding of green turtle foraging ecology is to identify and document the availability and quality of forage resources preferred by green turtles.
The diel foraging behavior of juvenile green turtles (Chelonia Mydas L.) ~ 7 to 8 kg in size was studies by visual observations from a fixed point and by acoustical tracking of three tagged animals, two of which were followed for >1 wk. Green turtles fed in a shallow seagrass-covered bay most commonly by day. There were usually two feeding bouts, one in the morning and one in the afternoon and each turtle visited a characteristic feeding area. Turtles were inactive at night and usually in mid-day in characteristic resting sites in coral reefs separated from the feeding sites by 0.2 to o.5 km. Pre-sunrise feeding activity was noted consistently in one tagged turtle while the other entered the feeding area later in the morning and remained there much of the day. Approximately 9 h per day were spent on the feeding sites by both turtles where the major food of one was determined by fecal examination to be turtle grass Thalassia testudinum König. Turtles were occasionally observed in groups of up to three, but they appeared to be generally solitary rather that social in their behavior.
The green turtle, Chelonia mydas, is a circumglobal species that exhibits several important developmental or ontogenetic shifts throughout its life history. The first major shift occurs when juvenile turtles migrate from pelagic habitat, where they forage as omnivores, to coastal neritic habitat, where they become primarily herbivores, foraging on algae and seagrass. Anecdotal evidence and gut-content analyses suggest that juvenile green turtles in south Texas bays, such as the lower Laguna Madre and Aransas Bay, undergo an additional ontogenetic shift during this important life history stage. Evidence from stable isotope analysis (SIA) of scute tissues of green turtles from Texas' lower Laguna Madre and Aransas Bay supports an intermediate stage between this species' shift from pelagic waters to seagrass beds in neritic waters; this additional shift comprises an initial recruitment of post-pelagic juveniles to jetty habitat located on the channel passes Gulf-ward of adjacent bays before subsequently recruiting to seagrass beds in these bays. Examination of stable carbon ([delta]13C) and nitrogen ([delta]15N) isotopes in microlayers of scute tissue from several size classes of green turtles from the lower Laguna Madre and Aransas Bay was used to confirm the occurrence of two ontogenetic shifts. Smaller green turtles (35 cm SCL) exhibited more depleted [delta]13C signatures and more enriched [delta]15N signatures, consistent with jetty habitat, compared to those of larger counterparts ( 45 cm SCL) that displayed enriched [delta]13C signatures and depleted 15N signatures, consistent with seagrass habitat. Changes in the isotopic composition between these size classes indicate distinct shifts in diet. Post-pelagic juveniles first recruit to jetty habitat and forage primarily on algae, before subsequently shifting to seagrass beds and foraging primarily on seagrass. These findings indicate the use of a characteristic sequence of distinct habitats by multiple life history stages of green turtles in Texas bays, a conclusion with broad management implications for this endangered species.
ABSTRACT: In recent years, scientists have recognized the need to conduct in-water studies to better understand the biology of juvenile sea turtles. Little is known regarding the seasonal abundance of juvenile populations in temperate developmental areas such as those in the Gulf of Mexico. It is likely that the Gulf of Mexico supports a year-round population of juvenile sea turtles.
Marine turtles are distributed in temperate, sub-tropical and tropical waters and beaches worldwide, often in areas heavily impacted by humans. Although there are many threats to marine turtle populations, the growing threats of nutrient pollution and harmful algal blooms are relatively understudied despite their widespread impacts on coastal marine ecosystems that marine turtles depend on. By studying juvenile green turtles (Chelonia mydas) in the Indian River Lagoon, Florida, where nutrient pollution and HABs are a widespread and longstanding issue, I aimed to conduct a case study of how these threats may affect this federally Threatened species. In Chapter 2, I used four concurrent, 18-year data sets to characterize and assess the interrelatedness of long-term trends in seagrass cover, macroalgae occurrence, juvenile green turtle abundance, and juvenile green turtle growth rates. From 2000 to 2018, IRL seagrass cover declined precipitously, macroalgae rose slowly through 2011 then declined during two severe HABs, juvenile green turtle abundance declined slowly, and growth rates declined through 2011 then rose through 2018. In Chapter 3, I conducted a 9-year study of juvenile green turtle foraging ecology using a comparative stable isotope approach. I found that carbon and nitrogen stable isotopic variance declined during and after two severe HABs in the IRL. In Chapter 4, I used two complementary methods to assess the diet of juvenile green turtles after two severe algal blooms in order to assess changes compared to previous diet studies. Visual identification of forage items showed that juvenile green turtle diet remained dominated by nutrient-tolerant red macroalgae with smaller components of seagrass and green algae; metabarcoding techniques largely failed to resolve their diet. My results highlight the web of complex effects and responses that factor in to determining the effects of nutrient pollution and HABs on juvenile green turtles. Future studies of habitat selection, foraging ecology, and the effects of these on juvenile green turtle growth and survival are needed to fully assess the threat of nutrient pollution.
Release of the 2000 Red List is a major landmark for IUCN. It is the first time that listings of animals and plants have been combined and the first time that the Red List has been produced on CD-ROM. The 2000 Red List combines new assessmentsincluding all bird species, many antelope and bat species, most primates and sharks, all Asian freshwater turtles, more molluscs, and many otherswith those from previous publications. The combination of animals and plants into a single list containing assessments of more than 18,000 taxa (11,000 of which are threatened species) and the move towards improved documentation of each species on the list means that a hard-copy version of the Red List would run to several volumes. This, combined with the fact that the Red List will be updated annually, led to the decision to release the Red List in electronic format, via the World Wide Web and as a CD-ROM.
Recent developments in open water research have refined our understanding of green turtle, Chelonia mydas, foraging ecology, but diet characterization among populations remains understudied. Previous hypotheses state that once young green turtles recruit to shallow water habitat they shift rapidly from an omnivorous to herbivorous diet. Supporting evidence has primarily been derived from traditional gut content analysis that only provides a small window in time to perceive the diet of an animal. In contrast, stable isotope analysis explore show a consumer uses its resources over a broad temporal scale. We tested the dietary shift hypothesis using gut content and stable isotope analyses to assess the nutritional ecology of a juvenile green turtle aggregation in the northern Gulf of Mexico. We examined the gut contents of 65 green turtles collected from 2008 and 2011 hypothermic stunning events in St. Joseph Bay, Florida. Gut contents were evaluated using volume, dry mass, percent frequency of occurrence, and index of relative importance (IRI). Juvenile green turtles showed omnivorous feeding behavior, feeding on a variety of animal and vegetal items with a bias towards seagrass and tunicates. In addition, we evaluated feeding consistency by stable isotope patterns from epidermis tissue. We measured the stable carbon (delta13C)and nitrogen (delta15N)isotope values in epidermis of 43 green turtles, ranging from 22.5 to 72.7cm in curved carapace length (CCLmin), and eight known prey items (e.g., algae, seagrasses, invertebrates) collected in 2011. Our study provides a foundation for characterizing the foraging ecology of green turtles in St. Joseph Bay and highlights the value of utilizing isotopic ecology for further foraging studies.
Marine biologist James R. Spotila has spent much of his life unraveling the mysteries of these graceful creatures and working to ensure their survival. In "Sea Turtles," he offers a comprehensive and compelling account of their history and life cycle based on the most recent scientific data and suggests what we can be done to save them. Illustrated with stunning, full-color photographs. 0-808-8007-6$24.95 / Johns Hopkins University Press
Sea Turtles: Field Research and Conservation is a comprehensive reference of experiences with sea turtle species from global experts. This book looks at the human side of protecting and studying these unique animals around the world, as well as the challenges involved, such as cultural differences and conducting research in remote locations. Led by a renowned expert in sea turtle conservation, this book addresses the largest issue facing sea turtle species currently; nearly all species of sea turtles are endangered due to poaching, fishing snares, climate change, and more. Chapters in this book range from the use of cutting-edge technology to learn more about this elusive reptile, to working with communities with long histories of sea turtle trade and consumption. It provides readers with firsthand accounts of sea turtle conservation efforts from conservationists based around the world and offers important suggestions and solutions for ensuring the future of these sea turtle species. Sea Turtles: Field Research and Conservation is the ideal resource for field biologist and marine conservationists, specifically those working in marine herpetology and with sea turtle species. Policymakers concerned with marine conservation, wildlife protection, and sustainable development, will also find this a useful reference for efforts and directions to enact change and save sea turtles from extinction. Offers examples of groundbreaking technology to conduct noninvasive sea turtle research Written by global experts working in the field to study and protect sea turtle species Includes human-to-human case studies and advice for collaborating with cultures and communities to save these endangered animals
