Green sea turtle swimming in a Brazilian estuary, highlighting genetic research and conservation.

Turtle Tales: Unlocking Genetic Secrets of Brazil's Green Sea Turtles

Rhea Morgan in Science & Nature August 2025 • 4 min read.

"Genetic Research Reveals Key Insights into the Diversity and Origins of Green Sea Turtles in a Vital Brazilian Estuarine Complex"

Sea turtles, ancient mariners of our oceans, undertake incredible journeys across vast distances. However, the lives of juvenile sea turtles remain largely a mystery. These young turtles spend much of their time in feeding grounds (FGs), areas where they can grow and mature. These FGs are often populated by turtles from various birthplaces, creating what scientists call 'mixed stock populations.'

A groundbreaking study focused on the green sea turtles (Chelonia mydas) inhabiting the Paranaguá Estuarine Complex (PEC) in Brazil. This unique location, a designated Natural World Heritage site, provides a crucial habitat for these creatures. Researchers sought to understand the genetic makeup of these turtles, trace their origins, and uncover aspects of their demographic history.

By analyzing mitochondrial DNA (mtDNA) from stranded green sea turtles within the PEC, scientists were able to compare their genetic signatures with those of nesting populations across the Atlantic. This allowed them to estimate the contributions of different rookeries (nesting sites) to the PEC feeding ground, revealing important connections and historical patterns.

Decoding the DNA: What the Genetics Reveal

Green sea turtle swimming in a Brazilian estuary, highlighting genetic research and conservation.

Researchers collected tissue samples from 60 stranded green sea turtles in the PEC. They then analyzed a specific region of their mitochondrial DNA (mtDNA). mtDNA is passed down from mother to offspring, making it a valuable tool for tracing lineages and population structures.

The mtDNA analysis identified several distinct haplotypes (genetic signatures) within the PEC green turtle population. When compared to other green turtle populations across the Atlantic, the PEC turtles showed significant genetic differences, highlighting the uniqueness of this group.

Genetic Diversity: The study identified seven main mtDNA haplotypes (CM-A1, CM-A5, CM-A6, CM-A8, CM-A10, CM-A32, and CM-A46). The most common was CM-A8, followed by CM-A5.
Natal Origins: Analysis revealed that the green turtles in PEC share genetic signatures with nesting females from Ascension Island, Guinea Bissau and Aves Island/Surinam.
Population Expansion: Genetic data suggests a population expansion occurred approximately 20,000-25,000 years ago, following the last Glacial Maximum.

The study also found that green turtles at PEC present genetic signatures similar to those of nesting females from Ascension Island, Guinea Bissau and Aves Island/Surinam. Population expansion was evidenced to have occurred 20-25 kYA, reinforcing the hypothesis of recovery from Southern Atlantic refugia after the last Glacial Maximum.

Protecting the Future of Brazil's Green Sea Turtles

This research provides critical insights for conservation efforts. By understanding the genetic diversity and origins of green sea turtles in the PEC, conservationists can develop more effective strategies to protect this vital habitat and ensure the long-term survival of these magnificent creatures. Protecting the PEC and similar feeding grounds is essential for the recovery of green sea turtle populations in the Atlantic.

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This article is based on research published under:

DOI-LINK: 10.1590/s1415-475738320140353, Alternate LINK

Title: Green Turtle (Chelonia Mydas) Genetic Diversity At Paranaguá Estuarine Complex Feeding Grounds In Brazil

Subject: Genetics

Journal: Genetics and Molecular Biology

Publisher: FapUNIFESP (SciELO)

Authors: Juliana Costa Jordão, Ana Cristina Vigliar Bondioli, Flavia Maria Guebert, Benoit De Thoisy, Lurdes Foresti De Almeida Toledo

Published: 2015-09-01

Everything You Need To Know

What is the significance of the Paranaguá Estuarine Complex (PEC) in Brazil for green sea turtles?

The Paranaguá Estuarine Complex (PEC) in Brazil is a significant feeding ground for green sea turtles. Genetic analysis of these turtles' mitochondrial DNA (mtDNA) reveals connections to nesting populations across the Atlantic. This is significant because understanding the genetic diversity and origins of these turtles is crucial for effective conservation strategies, especially in protecting vital habitats like the PEC, which are essential for the recovery of green sea turtle populations.

What is mitochondrial DNA (mtDNA), and why is it important in studying green sea turtles?

Mitochondrial DNA (mtDNA) is a specific type of DNA located in the mitochondria of cells, and it is passed down from mother to offspring. Analyzing mtDNA allows scientists to trace lineages and population structures of green sea turtles. This is important because by comparing mtDNA from different populations, researchers can determine the origins of turtles found in feeding grounds like the Paranaguá Estuarine Complex (PEC) and understand their genetic relationships.

What are haplotypes, and what do they reveal about green sea turtles in the Paranaguá Estuarine Complex (PEC)?

Haplotypes are genetic signatures found in mitochondrial DNA (mtDNA). Different haplotypes indicate genetic diversity within a population. In the green sea turtles studied at the Paranaguá Estuarine Complex (PEC), researchers identified several main mtDNA haplotypes, with CM-A8 being the most common. This is significant because understanding the distribution and frequency of different haplotypes helps assess the genetic health and diversity of the turtle population, informing conservation efforts. A higher diversity of haplotypes generally indicates a healthier, more resilient population.

What does 'natal origins' mean in the context of green sea turtle research, and why is it important?

The term 'natal origins,' in the context of green sea turtle research, refers to the nesting sites (rookeries) where the turtles were born. By analyzing the mitochondrial DNA (mtDNA) of green sea turtles in the Paranaguá Estuarine Complex (PEC), researchers can trace their genetic signatures back to specific nesting populations, such as those from Ascension Island, Guinea Bissau, and Aves Island/Surinam. Determining natal origins is important because it helps identify critical nesting areas and migration routes, allowing for targeted conservation efforts to protect these vulnerable populations at all stages of their lives.

What does the term 'population expansion' mean, and what does it suggest about the history of green sea turtles?

Population expansion, in this context, refers to a period of growth in the green sea turtle population size. Genetic data suggests that a population expansion occurred approximately 20,000-25,000 years ago, following the last Glacial Maximum. This is significant because it suggests that the green sea turtle population recovered from a period of decline, possibly due to climate change or other environmental factors. Understanding these historical population trends can provide insights into the resilience of green sea turtles and inform strategies for managing their populations in the face of current and future environmental challenges.