Today we celebrate one of the most ancient marine populations on our planet.
Sea Turtles
In total, seven distinct species of sea turtles inhabit all tropical and subtropical seas of our planet. From a zoological perspective, however, only six actually belong to the sea turtle family (Cheloniidae = hard-shelled sea turtles). The leatherback turtle represents its own genus and is the sole surviving species of the family Dermochelyidae.
The following characteristics serve to distinguish between the individual species:
Flatback sea turtle (flat back sea turtle - Natator depressus): This species nests and resides exclusively in the tropical waters of the Australian-New Guinean continental shelf. Unlike the hatchlings of other species, flatback sea turtle hatchlings do not disperse into the open ocean, but remain over the continental shelf.
Hawksbill sea turtle (hawksbill turtle - Eretmochelys imbricata): Driven to the brink of extinction due to the trade in its shell (tortoiseshell), this species is classified as "Critically Endangered" on the IUCN Red List of Threatened Species. It is easily distinguished by its hawk-like beak.
Green sea turtle (Green sea turtle - Chelonia mydas): The fat underneath its carapace is green, as it is the only sea turtle species that subsists on an almost strictly herbivorous diet (adult individuals only).
Loggerhead sea turtle (Loggerhead sea turtle - Caretta caretta): This species possesses a robust head with powerful jaws adapted for crushing hard-shelled prey.
Kemp's ridley sea turtle (Kemp’s ridley sea turtle - Lepidochelys kempii): This is the smallest species of sea turtle. It nests in mass synchronized nesting aggregations (arribadas) and is the only species to nest primarily during the daytime.
Olive ridley sea turtle (Olive ridley sea turtle - Lepidochelys olivacea): This is the most abundant sea turtle species. It nests both in mass synchronized nesting aggregations (arribadas) and individually. Its carapace has a slightly heart-shaped profile.
Leatherback sea turtle (Leatherback sea turtle - Dermochelys coriacea): It dives to depths of up to 1,200 m when foraging and possesses a specialized counter-current heat exchange system to maintain its core body temperature in colder waters.
Conservation Status and Threats
Turtles are among the oldest marine inhabitants on Earth. They have inhabited the oceans since the era of the dinosaurs, persisting through environmental shifts for over 100 million years. Yet, what natural disasters and ice ages failed to achieve, human activities have accomplished in just a few centuries: driving these species to the brink of extinction. The pressures are diverse, but they share a common thread: they are anthropogenic. Today, sea turtles face a multitude of existential threats:
Marine Debris and Pollution
- Turtles frequently become entangled in drifting fishing nets and lines. Since they must surface to breathe within a maximum of 45 minutes, such incidents are often fatal.
- Drifting plastic bags are mistaken for jellyfish, a primary food source. Because plastic cannot be digested, it obstructs the gastrointestinal tract, causing the animals to starve with a full stomach.
- Nesting beaches are rendered inaccessible by marine debris washed ashore.
Coastal Development and Light Pollution
- Nesting beaches are degraded or rendered inaccessible by tourism activities.
- Obstacles on the beach (such as sun loungers) prevent female turtles from finding suitable nesting sites. For hatchlings, such obstacles are often impassable and rapidly become lethal traps.
- Upon emerging, hatchlings orient themselves toward the sea by seeking the brightest horizon. However, artificial light sources near the nesting beach can disorient the hatchlings, causing them to move inland.
Bycatch
An estimated 250,000 sea turtles drown annually due to longline fisheries and gillnets.
Vessel Strikes
Turtles frequently collide with vessel propellers, resulting in severe physical trauma.
Climate Change
- Female turtles exhibit high natal homing fidelity, returning to nest on the exact beach where they hatched. However, storm surges and rising sea levels can lead to the permanent loss of nesting beaches, with long-term impacts that are not yet fully understood.
- The sex of turtle hatchlings is determined by incubation temperature. Excessively high average nest temperatures result in exclusively female hatchlings, leading to biased sex ratios in the population.
Poaching
Despite increased anti-poaching enforcement in many nations, turtles continue to be targeted for their meat, and hawksbill turtles for their tortoiseshell. Turtle eggs also remain highly sought after as a delicacy in several regions.
All 7 species are listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), representing the highest level of protection. Consequently, international commercial trade in specimens or derived products is prohibited.
Why protect sea turtles?
Sea turtles function as keystone species within marine ecosystems.
- The hawksbill sea turtle feeds on marine sponges, thereby regulating sponge populations and protecting reef structures. Uninhibited growth of sponges would outcompete reef-building corals, destabilizing the reef ecosystem.
- Green sea turtles maintain the health of seagrass meadows. By grazing selectively on young, nitrogen-rich seagrass blades, they facilitate continuous seagrass regeneration.
Conserving sea turtles is essential to maintaining the ecological equilibrium of the oceans.
They are not only ancient organisms, but also vital components of marine ecosystems. Their loss would disrupt the complex trophic interactions between marine plants, animals, and habitats.
Their conservation is therefore more than a matter of ethical concern—it is a critical ecological responsibility for our planet.
Sources:
Ashlan Cousteau, Philippe Cousteau, Ozeane für Dummies, Weinheim, Wiley-VCH 2021
Christine Figgener, Meine Reise mit den Meeresschildkröten, München, Piper Verlag 2023
Esther Gonstalla, Das Ozean Buch, 2nd ed., München, Oekom Verlag 2021
https://www.turtle-foundation.org/meeresschildkroeten/artenportraits/
https://www.turtle-foundation.org/meeresschildkroeten/bedrohungen/
https://www.stiftung-meeresschutz.org/foerderung/meeresschildkroeten/
