Long-term Changes in Juvenile Green Turtle Abundance and Foraging Ecology in the Indian River Lagoon, Florida
Long-term Changes in Juvenile Green Turtle Abundance and Foraging Ecology in the Indian River Lagoon, Florida

Author: Christopher Augustus Long

Publisher:

Published: 2021

Total Pages: 0

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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.

Ecological Correlates of the Abundance of Juvenile Green Sea Turtles (Chelonia Mydas) on Nearshore Reefs in Southeast Florida
Ecological Correlates of the Abundance of Juvenile Green Sea Turtles (Chelonia Mydas) on Nearshore Reefs in Southeast Florida

Author: Melanie Stadler

Publisher:

Published: 2013

Total Pages: 41

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Juvenile green turtle (Chelonia mydas) abundance differs among nearshore reefs, but why some sites are preferred over others is unknown. My study had two objectives: to quantify differences in abundance over time (one year) and to determine what ecological factors were correlated with those differences. I conducted quarterly surveys on reefs in Palm Beach and Broward Counties and compared reef sites with respect to (i) water depth, (ii) algal abundance and composition, and (iii) changes in reef area (caused by sand covering) through time (11 years). Turtles were most abundant on shallow reefs exposed to high light levels that remained stable (uncovered by sand) for long periods of time. These reefs had the highest diversity of algal species, in part because cropping by the turtles prevented any one species from becoming dominant. My results suggest that both physical and biological factors make some reefs more attractive to turtles than other

Home Range and Habitat Use of Juvenile Green Turtles in a Shallow Tidal Environment
Home Range and Habitat Use of Juvenile Green Turtles in a Shallow Tidal Environment

Author: Meagan Gary

Publisher:

Published: 2017

Total Pages: 48

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The home range can be further understood by examining: (1) environmental factors that are responsible for its selection, and (2) habitat use. Green turtle (Chelonia mydas) home ranges are characterized by their food abundance, distribution, and quality. The shallow water habitats of The Bahamas are important foraging sites for juvenile green turtle. The goal of this study was to determine how turtles use their home range at a tidal foraging site. I tracked turtle home range using acoustic telemetry. I conducted esophageal lavage on tracked turtles and mapped the vegetation coverage. Turtle home ranges were small, and often overlapping areas (mean ± SD= 0.64 ± 0.24 km2). Turtles consumed primarily seagrass (Thalassia testudinum), which was concentrated inside the tidal creek. This study documented the smallest recorded home ranges of juvenile green turtles and examines the combination of the effects of tide, temperature, and vegetation on green turtle home range.

Ecology of Juvenile Green Turtles, Chelonia Mydas, at a Temperate Foraging Area in the Northeastern Gulf of Mexico
Ecology of Juvenile Green Turtles, Chelonia Mydas, at a Temperate Foraging Area in the Northeastern Gulf of Mexico

Author: Erin McMichael

Publisher:

Published: 2005

Total Pages:

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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.

New Perspectives on the Pelagic Stage of Sea Turtle Development
New Perspectives on the Pelagic Stage of Sea Turtle Development

Author: Archie Carr

Publisher:

Published: 1986

Total Pages: 44

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"Thirty years ago when interest in sea turtles was beginning to spread, the ,habitat of the post-hatchlings for all the species was unknown. After they left the nest and made their way through the surf, they simply disappeared. Very slowly, data to suggest a pelagic life in a sargassum weed habitat accumulated, and eventually I received support to investigate that idea intensively. By the end of that research period it was clear that when sargassum rafts are present in longshore arrays within the swimming range of the hatchlings, they do in fact enter them (Carr 1982). It followed that the early developmental stages are pelagic, with the corollary that, because sargassum accumulates along convergences, the adjacent currents may carry the rafts and their occupants on journeys of either local or oceanic extent or both"--Introduction.

Juvenile Green Turtle (Chelonia Mydas) Foraging Ecology
Juvenile Green Turtle (Chelonia Mydas) Foraging Ecology

Author: Eliza Inez Gilbert

Publisher:

Published: 2005

Total Pages: 47

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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.

Genetic Structure of Green Sea Turtle (Chelonia Mydas) Foraging Aggregations on the East Coast of Florida
Genetic Structure of Green Sea Turtle (Chelonia Mydas) Foraging Aggregations on the East Coast of Florida

Author: Monica R. Reusche

Publisher:

Published: 2020

Total Pages: 26

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The genetic structure of juvenile green turtles (Chelonia mydas) foraging on the east coast of central Florida is not well understood, nor has it been examined over time. In the last three decades, the dramatic increase in the number of green sea turtle nests in Florida, in association with other population parameters, has led to this species being down-listed under the Endangered Species Act from “endangered” to “threatened” in the northwest Atlantic. However, it was unclear if the exponential growth in Florida nest numbers had any influence on the genetic structure of juveniles in nearby foraging aggregations. To understand this potential impact mixed-stock analysis was conducted using mitochondrial DNA fragments that were over 800 base pairs long on samples taken from juveniles captured from 2002-2005 and 2016-2018 in the central Indian River Lagoon and Trident Submarine Basin in Port Canaveral. Results indicate the sampled foraging sites are genetically distinct habitats. In both sites, recruitment from Florida nesting beaches remained low despite increases in nesting while contributions from rookeries in Costa Rica and Mexico dominated both foraging aggregations across time. Haplotype diversity and nucleotide diversity decreased at both foraging sites over time. The foraging sites shared the two most frequently occurring haplotypes, but also had haplotypes that were unique to the site or sample period. Our results highlight the need for broader sampling of rookeries and foraging aggregations to understand the impacts of nesting increases in one rookery on juvenile diversity. Future studies should include all life stages of green turtles to enhance understanding of both the census population and effective population to better inform conservation policies necessary for a continued recovery.

Spatial Distribution and Abundance of Large Green Turtles on Foraging Grounds in the Florida Keys, USA
Spatial Distribution and Abundance of Large Green Turtles on Foraging Grounds in the Florida Keys, USA

Author: Ryan Charles Welsh

Publisher:

Published: 2019

Total Pages: 38

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Discerning distribution, density, and abundance of organisms is essential for conservation and management of imperiled species. However, simple counts of sampled individuals are often not adequate to make such estimates, this is especially true for large and highly mobile marine animals. Green turtles (Chelonia mydas) are a highly migratory, long-lived, late-maturing, marine megafauna, that is beginning to recover from severe global population declines. Distance sampling techniques can be used to generate estimates of abundance of green turtles in foraging grounds which have been relatively unstudied in the Northeastern Atlantic basin, filling in important data gaps in a species that is of critical conservation concern. The Quicksands foraging grounds located west of Key West, Florida, USA is used by both sub-adult and adult green turtles. Standardized transects were performed 18 times between 2006-2018, and using the collected data; abundances, spatial distribution and evidence of spatial segregation were generated through density surface models and null mode analysis. Densities of foraging green turtles rival some of the largest densities known in the world. Spatial segregation of the two size classes is evident on the foraging ground and may be attributed to differing predator detection and avoidance strategies of the size classes Finally, given the high densities of animals found on the foraging grounds and the rise in general population levels of green turtles and drop in population of green turtle predators (i.e. large sharks), concern is raised for the long term sustainably of the Quicksands seagrass pastures.

Foraging Ecology of Green Turtles (Chelonia Mydas) on the Texas Coast, as Determined by Stable Isotope Analysis
Foraging Ecology of Green Turtles (Chelonia Mydas) on the Texas Coast, as Determined by Stable Isotope Analysis

Author: Catherine Concetta Theresa Gorga

Publisher:

Published: 2011

Total Pages:

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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.