Green turtles (Chelonia mydas) are marine reptiles found in tropical and subtropical waters worldwide. These creatures undergo a notable dietary transformation throughout their lives. Their feeding habits shift significantly from early developmental stages to adulthood, influencing their growth and role within marine ecosystems. Understanding these changes provides insight into their biology and the environments they inhabit.
The Initial Diet of Young Green Turtles
Young green turtles are omnivorous, consuming various food sources to support their rapid growth. As hatchlings, they primarily feed on animal matter near the ocean surface, accessible due to their weaker swimming abilities. This includes small invertebrates like crabs, jellyfish, worms, and crustaceans, along with fish eggs, hydrozoans, and bryozoans.
This protein-rich diet is important for providing energy for their initial development. As they grow, they incorporate marine plants like algae and seaweed. This mixed diet provides nutrients during their pelagic (open ocean) phase before transitioning to coastal habitats.
The Primary Diet of Adult Green Turtles
As green turtles mature, they undergo a dietary shift, becoming almost exclusively herbivorous. This transition occurs when they reach a carapace length of 20 to 25 cm, or approximately five years of age, as they recruit to nearshore foraging grounds. Their adult diet consists of seagrasses and marine algae. Common items include green and red algae, sea lettuce, crinkle grass, green seaweed, and seagrass species like Thalassia testudinum (turtle grass).
Green turtles possess adaptations that allow them to process tough plant material. Their jaws are finely serrated, functioning like a saw to scrape algae off rocks and tear grasses and seaweeds. Internally, they utilize hindgut fermentation, where specialized cellulolytic microbes in their cecum and proximal colon break down complex plant matter. This digestive process enables them to extract nutrients from their fibrous diet, which is unique among sea turtles as most other species remain carnivorous or omnivorous into adulthood.
The Ecological Significance of Their Feeding Habits
The feeding habits of adult green turtles impact marine ecosystems, particularly seagrass beds. They are often called “lawnmowers of the sea” due to their grazing. By consistently cropping seagrasses, they prevent overgrowth, maintaining the health and productivity of these underwater meadows. This grazing stimulates new, more nutritious growth, benefiting both the turtles and other species that rely on these habitats.
Their foraging activities also contribute to nutrient cycling within marine environments. Grazing by green turtles helps aerate sediments and prevents anoxia, a condition where oxygen is depleted. By consuming older seagrass biomass, they redistribute digested nutrients throughout the habitat via their feces, enriching the environment. These actions ensure the vitality of seagrass ecosystems, which serve as breeding grounds and shelter for marine organisms.