For millions of years, countless sea turtles have sailed in the world’s oceans and migrated great distances between feeding sites and nesting beaches. But today, those long journeys repeatedly expose them to negative environmental changes and man-made impacts that are detrimental. Despite global conservation efforts, all seven species of sea turtle are Endangered or Critically Endangered at global or regional levels.
The mass movement of these and other animals, whether by land, sea or air, represents one of the great wonders of the planet and weaves crucial living threads that strengthen the structure of the ecosystem.
Now, for multiple reasons—including human-caused physical hazards, climate change, habitat loss, and many others—the fabric of these global ecostructures is rapidly breaking down. Species are disappearing at unprecedented rates and biodiversity loss is disrupting natural systems, imposing adverse impacts on the world’s migrant species.
The important question is: Can sea turtles, people, and conservation strategies evolve fast enough to protect those epic migrations and the animals that make them?
A leatherback turtle laying eggs. Image courtesy of Florida USFWS.
Crossing planetary boundaries poses multiple threats
Biodiversity is one of nine planetary boundaries that allow for a “safe operating space for humanity,” according to an interdisciplinary team of scientists convened by the Stockholm Resilience Center. The other eight limits that humanity must avoid exceeding are climate change, ocean acidification, land use change, freshwater use, ozone depletion, aerosol air pollution, biochemical flows (imbalances in nitrogen and phosphorus cycles) and the presence of other pollutants.
Humanity has already breached the “core limits” of biodiversity loss and climate change, and is stepping on the threshold of biochemical flows and land-use change. While exceeding one of the core boundaries could destabilize the Earth systems that sustain humanity completely, crossing any of the boundaries also risks destabilizing others and creating a domino effect. In the coming decades, human activities will put one million more plant and animal species at risk of extinction according to the 2019 report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).
“Biodiversity and nature’s contributions are our common heritage and the most important ‘safety net’ for humanity’s life support,” said Sandra Diaz, an Argentine ecologist who co-chaired IPBES in 2019. “But our safety net is stretched almost to the point of breaking.”
Baby leatherback turtles go from the nest to the sea in Aruba. Image by Elise Peterson on Wikimedia Commons (CC BY 3.0).
Turtles at additional risk from exceeding boundaries
Sea turtles have a tenuous and unenviable position in the context of planetary boundaries. Its life cycle requires a safe crossing by sea and land. Lued turtle migrations, for example, can cross the borders of more than 30 countries.
As humanity rapidly approaches planetary boundaries, it puts these intrepid sailors ever closer to suffering damage from various origins. If conservation efforts cannot reverse turtle losses, their critical situation could be a precursor to the extinction of other migratory species, including perhaps the world’s largest migrant: Homo sapiens.
Read more | What happened to the Galapagos sea turtles when tourism was halted due to the pandemic?
The most well-known threats to sea turtles have to do mostly with the planetary limit of biodiversity (bycatch and theft of eggs from nests, for example), and the limit of land use change (loss of habitat and nesting sites).
Now, being redefined in the context of other transgressions to planetary boundaries, turtles face a range of new dangers that we understand little.
Assault on nesting beaches
Sea turtles are most visible to us when females come to shore to lay eggs, and that’s the habitat that science studies the most. Climate change is a planetary boundary that we know is altering the beaches on which turtles nest and spend a brief but critical portion of their lives, and raises multiple existential challenges. For example, as the sex of turtles depends on temperature, more females are being born as global warming pushes up temperatures on nesting beaches. Currently, there are three female turtles for every male in many parts of the world.
“But how does feminization affect populations?” asks Mariana Fuentes, a marine conservation biologist at Florida State University. “How many males do there have to be for populations to be sustained? We don’t know.”
The presence of other pollutants, another planetary boundary, could act synergistically with global warming and warm the beach even more. Human-based microplastics could increase the temperature of sand, says Fuentes, who studies the evolution of sand’s thermal profile.
Clearly, all of those females will need nesting beaches with optimal incubation environments, a key factor in the resilience of global turtle populations, Fuentes adds. But another limit, land-use change, is reducing the availability and suitability of nesting sites. As climate change intensifies, there will be more severe and more frequent storms that will erode more beaches, and primary nesting sites could disappear. Simultaneously, rising sea levels due to climate change and the “shielding” of coastlines with human constructions, especially dikes, will worsen the nesting situation.
Turtles have adapted and moved to new nesting areas in the past, but, as humanity blocks access to beaches, will there be enough suitable nesting sites?
A 9 cm sea turtle calf and the pieces of plastic that were found in its gastrointestinal tract. This amount of plastic could take up the space for food the calf needs to grow quickly and be less easy prey, says Jennifer Lynch, co-director of the Marine Debris Research Center at Pacific University of Hawaii in Honolulu. Image courtesy of Jennifer Lynch.
Read the full report on Mongabay
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