Green sea turtles are large marine reptiles found in tropical and subtropical waters around the world. These mariners undertake impressive migrations across ocean expanses. Their appearance and nature make them captivating, prompting interest in their diet and daily lives.
The Herbivorous Diet of Adult Green Sea Turtles
Adult green sea turtles are primarily herbivores, unique among sea turtles. Their diet consists exclusively of seagrasses and marine algae, which they graze in shallow coastal waters. This diet gives their fat a greenish hue, the origin of their common name.
Their specialized jaws are well-adapted for this diet. Green sea turtles possess serrated beaks, which allow them to effectively crop seagrass blades and scrape algae from hard surfaces. Common seagrass species they consume include turtle grass (Thalassia testudinum), shoal grass (Halodule wrightii), and manatee grass (Syringodium filiforme).
Dietary Changes in Young Green Sea Turtles
The diet of green sea turtles undergoes a significant shift as they mature. Unlike herbivorous adults, young green sea turtles are omnivores. Their early diet is more diverse, reflecting a need for different nutrients during rapid growth.
Their diet includes invertebrates (crabs, shrimp, mollusks, worms, jellyfish), fish eggs, hydrozoans, bryozoans, and plant matter like algae and seaweed. As they grow, typically once they reach a carapace length of about 200 mm (around 8 inches), their diet gradually transitions, with plant matter becoming a dominant component until they become fully herbivorous.
The Ecological Importance of Their Diet
The grazing habits of adult green sea turtles play an important ecological role in marine ecosystems, especially in seagrass meadows. They are often referred to as “lawnmowers of the sea” due to their grazing. This continuous cropping of seagrass helps maintain the health and productivity of these habitats.
Their feeding prevents seagrass overgrowth, which can otherwise obstruct currents, shade the seafloor, leading to decomposition and unhealthy conditions. By consuming older growth and promoting new shoots, green sea turtles stimulate seagrass productivity and nutrient cycling. This action benefits other marine species that rely on seagrass meadows for food, shelter, and breeding, thereby contributing to biodiversity and stability of coastal environments.
What Not to Feed Green Sea Turtles
Feeding green sea turtles human food or foreign objects is harmful. Such actions can lead to negative consequences. Human food is not nutritionally appropriate and can cause digestive problems or nutritional deficiencies, impacting long-term health.
Interacting with humans for food alters their natural foraging behaviors, making them associate people with meals. This causes turtles to approach boats or swimmers, increasing their risk of injury from propellers or fishing gear entanglement. They may also accidentally ingest plastic debris, mistaking it for food, causing internal blockages or toxicity. Observing green sea turtles from a respectful distance is the most responsible way to appreciate them.