The green sea turtle food chain is unique since their predatory diet is clearly defined as carnivorous youth and herbivorous adult. Archie Carr originally described the maturation at sea as the “lost years” since studies have not been able to determine why the diet preference shifts from pelagic carnivore to nearshore herbivore. What is not lost is the appreciation and complexity of the green sea turtle diet.
Hatchling green sea turtle food chain includes dining on easy prey once their attached yolk sac is depleted. They eat whatever crosses their path as they swim to Sargassum algae islands in the open waters. They consume jellyfish, small mollusks, crustaceans, sponges, ctenophores, larval crabs, and shrimp, macroplankton, invertebrates, barnacles, fish larvae and terrestrial wind-blown ants, beetles, leafhoppers, and flies while swimming among Sargassum algae near Bermuda in the North Atlantic gyre. While these Sargassum archipelagos serve the turtle food chain by acting as dinner cruises for a number of sea turtle hatchlings, it has been observed that the juvenile greens will swim the open waters and choose a resident feeding location until they mature and decide to head to nearshore areas.
Herbivorous adults search seagrass territory to reside. Green sea turtles have beaks with a serrated ridge instead of teeth and their keen underwater vision and ability to see color are desirable attributes for a seagrass hunter. Green sea turtles have been observed eating green and red algaes, Zostera, Cymodocea, Thallasia, Halophila, Syringodium, Posidonia, Halodule; Chaetomorpha, Sargassum, and Hyphea species. In general, green sea turtles will eat less during mating season.
Green sea turtles are challenged to find intake resources like freshwater, protein, and vitamin D; making salt management, food type, and sunlight driving forces in this established food chain.
Salt management is a function of the circulatory system, esophagus, and a salt gland located behind the eyes. Physiology allows for salt to be concentrated and expelled by the salt gland. Salt water intake is reduced since the esophagus is lined with papillae that hold incoming food so throat muscles can contract and expel any salt water that is taken in with food consumption. Green sea turtles prefer nearshore areas and estuaries for their adult feeding grounds since salinity (salt concentration) is lower in these areas as flow from freshwater rivers and streams dilute the salty waters.
To help obtain protein, Atlantic turtles prefer shallow, sandy seagrass flats and select “grazing plots” to chomp since new growth seagrass contains more protein than older seagrass. Eastern Pacific species will reside among coral reefs and have been observed capturing sponges, mollusks, fish, polychaete worms, and jellyfish while foraging in seagrass beds. In captivity, Chelonia mydas species are strictly omnivorous since seagrass beds are not an abundant protein source.
Green sea turtles sunbathe on beaches and reside in shallow waters to supplement vitamin D from sunlight.
Ripple, Jeff. Sea Turtles. 1996. Voyageur Press. MBI Publishing Company, St. Paul MN pgs. 61-66, 16-23.
Ingle, Robert. Sea Turtles and the Turtle Industry of the West Indies, Florida, and the Gulf of Mexico. 1949. University of Miami Press. Parker Art Printing Association, Coral Gables Florida pgs. 21-22,31,37-38.
Spotila, James R. Sea Turtles. 2004. The Johns Hopkins University Press. Baltimore, Maryland pgs. 97-109
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