Species Description: The common name for the endangered green turtle, Chelonia mydas (Linnaeus, 1758), is derived from the green color of its body fat. It has one pair of prefrontal scales on the head and the lower jaw has a strongly serrated edge. The heart-shaped carapace is serrated posteriorly and lacks a vertebral keel. Scutes on the carapace are olive, yellowish and brown, often with mottling or wavy or radiating patterns (Ernst and Barbour 1989).
Regional Occurrence: The green turtle is a circumglobal species with foraging and nesting occurring throughout the tropics.
IRL Distribution: Chelonia mydas is found throughout the Indian River Lagoon.
Age, Size, Lifespan: Adult green turtles weigh between 110-205 kg (250-450 lbs), with lengths averaging 91-122cm (36-48 in.).
Reproduction: Sexual maturity estimates range from 12-35 years with Lutz and Musick (1997) reporting 25-35 years. However, Female green turtles may typically mature at 8 to 25 years of age (J. Provancha - pers. comm.). Copulation occurs at sea at no particular time of day or night, and nest deposition occurs predominately at night on ocean beaches with well-drained sand dunes. It is estimated that individual green turtles nest approximately three times per season and have remigration intervals of 2.86 years. The result is that in some years large numbers of turtles have cycles that match, therefore yielding considerably higher nesting densities in a given location (Miller 1997).
Nests are clutches of approximately 112 eggs requiring up to 60 days to develop and hatch. Several factors affect the sexual determination of sea turtle hatchlings but much of it can be accounted for by sand temperature around the nest site. Generally, the higher the temperature of the nest environment is above the critical temperature, the more females are produced (Mrosovsky and Yntema 1980).
Temperature: The behavior and distribution of this species is obviously affected by cold temperatures that are common in the northern IRL area during January and February. When water temperatures within the IRL drop below 8 °C, turtles become lethargic and float to the surface (Witherington and Ehrhart 1989). During the winter period they roam greater distances and in unpredictable patterns within the lagoon when compared to summer activities. The atypical movements during winter are assumed to be attempts to leave the lagoon which, due to its configuration, acts as a trap (Mendonca 1983).
Trophic Mode: Young green turtles are omnivorous. Among other things, their gut contents often include ctenophores, insects, pelagic snails, and small fish (Carr 1986). As they move into various habitats, they adapt their diets to their new surroundings. Juvenile greens shift to herbivory, which includes the consumption of macroalgae and seagrasses (Mendonca 1983, Green 1993, Balaz 1982).
Competitors: Nest Predators: Predation on nests by raccoons (Procyon lotor) and to a lesser degree, feral pigs, cats and ghost crabs is an additional threat. The levels of predation vary with the area and predator control methods. In other regions of the world, predators include foxes, jaguars, ghost crabs and humans.
Habitat: At various of its life stages, the green turtle utilizes bays, lagoons, and the mouths of rivers. As with other sea turtles, nesting adults migrate to ocean beaches to deposit their eggs for incubation. Although nesting in Florida appears to be increasing in the late 1990's, key nesting sites are found in Costa Rica, eastern Surinam, islands off of Queensland, Australia and Ascension Island (Ernst and Barbour 1989).
Green turtle hatchlings from Florida emerge from the nesting beach and enter the sea, swimming out to the Sargassum driftlines where they find shelter and food (Carr 1986). These post-hatchling greens apparently drift with oceanic circulation patterns toward the eastern Atlantic where they forage and grow along the Azores and Canary Islands. In the vicinity of the IRL, green turtles use both beach and estuarine habitat areas. The estuary provides a developmental habitat for immature greens (post-yearling to subadults). The Mosquito Lagoon probably represents the northernmost winter range for this species. Mendonca and Ehrhart (1982) estimated this population to be about 135 animals but later, Witherington and Ehrhart (1989) speculated that the population was growing, based on data from cold stunning events. During the winter of 1989, 209 greens were found stunned in Mosquito Lagoon after a cold period (Schroeder et al. 1990).
The beaches along the IRL provide nesting habitat for green turtles, although their numbers relative to loggerhead turtles are quite low. Greens account for about 2% of the sea turtle nests deposited along IRL area beaches.
Special Status: Endangered Species
Notes on Special Status:: The green turtle, listed by the USFWS as an endangered species, is commercially valued in many countries for its meat, eggs and calipee (the cartilaginous portions of the shell). Threats to the species are numerous and include habitat alteration, boat strikes, nest predation, oil pollution, entanglement, marine debris, disease and incidental capture is fisheries. Until the 1970's, the harvesting of turtle eggs in Brevard County was not uncommon.
As with other sea turtle species, continued existence of this species is severely threatened by human impacts, especially from fishing operations. Shrimp trawlers in particular (Lowe et al. 1990) cause the majority of incidental deaths of sea turtles. Nest predation is an additional threat, particularly in areas where no predator control methods are employed around nest sites. Additionally, disorientation and misorientation of newly emerged turtles is becoming an increasing threat to the species along Florida's coast and many other locations in the world. Various human structures with bright nighttime lighting have been implicated in disorientation events (Raymond 1984, Witherington 1992) which lead turtle hatchlings away from the ocean and into roads and other hazards.
An additional threat to this species is a disease known as fibropapillomatosis, an epizootic affecting a variety of species, but which has been primarily reported for the green turtle. Lesions resulting from the disease have been documented since 1938 but have been noted worldwide with increasing frequency since the late 1980's (Herbst 1994). The disease appears most frequently in juveniles and to date the etiological agent is unproven.
Benefit in the IRL: Aesthetic
Economic Importance: None currently. However, the Florida fishery for immature green turtles was not outlawed until 1974. 19th century reports indicate the green turtle fishery in the region began in about 1878, with the species becoming severely diminished over a period of 17 years of heavy exploitation. Fisheries data for the Mosquito Lagoon in the late 1800s indicated that green turtles were often exported from Florida, with as many as 150 greens exported in 1879. By 1895 captures of estuarine green turtles declined dramatically (Ehrhart 1983).
Balazs GH. 1982. Status of sea turtles in the central Pacific Ocean. In: Biology and Conservation of Sea Turtles. 243-252. Washington, DC: Smithsonian Institution Press.
Carr A. 1986. Rips, FADS, and little loggerheads. Biosci 36: 92-100.
Ehrhart LM. 1983. Marine turtles of the Indian River Lagoon system. Fla Sci 46: 337-346.
Ernst CH, Barbour RW. 1989. Turtles of the World, Vol. 388. Washington, DC: Smithsonian Institution Press.
Green D. 1993. Growth rates of wild immature green turtles in the Galapagos Islands, Ecuador. J Herpetol 27: 338-341.
Herbst LH. 1994. Fibropapillomatosis of marine turtles. Ann Rev Fish Diseas 4: 389-425.
Lutz PA, Musick JA. 1997. The biology of sea turtles. Chelonian Conserv Biol 2: 463-463.
Mendonça MT. 1983. Movements and feeding ecology of immature green turtles (Chelonia mydas) in a Florida lagoon. Copeia 1983: 1013-1023.
Mendonça MT, Ehrhart LM. 1982. Activity, population size and structure of immature Chelonia mydas and Caretta caretta in Mosquito Lagoon, Florida. Copeia 1982: 161-167.
Miller JD. 1997. Reproduction in sea turtles. In: Lutz PL, Musick JA, Eds. The biology of sea turtles. 51-80. Boca Raton, FL: CRC Press.
Mrosovsky N, Yntema CL. 1980. Temperature dependence of sexual differentiation in sea turtles: Implications for conservation practices. Biol Conserv 18: 271-280.
Raymond PW. 1984. Sea turtle hatchling disorientation and artificial beachfront lighting: a review of the problem and potential solutions. Center for Environmental Education: Washington, DC.
Schroeder BA, Ehrhart LM, Guseman JL, Owens RD, Redfoot WE. 1990. Cold stunning of marine turtles in the Indian River Lagoon System, Florida, December 1989. In: Richardson TH, Richardson JI, Donnelly M (compilers). 67-69. Proc Tenth Annual Workshop Sea Turtle Biol Conserv. NOAA Technical Memorandum NMFS-SEFC-278.
Witherington BE. 1992. Behavioral responses of nesting sea turtles to artificial lighting. Herpetologica 48: 31-39.
Witherington BE, Ehrhart LM. 1989. Hypothermic stunning and mortality of marine turtles in the Indian River Lagoon System, Florida. Copeia 1989: 696-703.