Temperature Effects on Sea Turtle Sex Ratios and the Potential Impact of Climate Change
Admittedly, I know very little about sea turtles. After starting my internship at the National Marine Life Center I decided to order a book specifically dedicated to the biology and behavior of these mysterious oceanic reptiles. One interesting fact I came across while reading was that the temperature at which the eggs are incubated determines whether or not the turtle will be male or female.Most vertebrates have sex chromosomes (XX for female and XY for male), however, sea turtles lack these chromosomes.
Females need warmer temperatures in order to develop. For example, in green turtles, temperatures need to be 88 F or above for the eggs to become females. For males to develop the temperature is around 82 F. If the temperature of incubation falls somewhere between 82 and 88 F, a mixture of the sexes develop. Heat produced by the eggs themselves can also contribute to the incubation temperature – eggs in the center of the nest become females and the eggs along the periphery become males (Spotila 2004).
If temperature affects the sex ratio of sea turtles, how might climate change impact populations in the future? Currently, sea turtle populations that nest in the southern portion of the United States are predominately female biased. It has been suggested (Hawkes 2007) that if there is even a 1 C warming of average temperatures, an even more significant bias could occur. If average warming exceeds 3 C, mortality rates of the eggs may also occur.
Climate change may also affect the nesting grounds of turtles if sea levels rise. Beaches currently being used by turtles may vanish under the sea. Ocean acidification (caused by increased CO2 levels) could potentially alter the sediment of the beaches, which may lead to inadequate conditions for incubation (Fuentes et al 2011). Sea turtles select their nesting sites based on several factors, such as low salinity, sufficient space above the hide tide line, adequate vegetation (for some species), high humidity, etc (Hawkes 2007). All of these may be affected by an increase in average global temperatures.
Future studies need to be conducted to better estimate the current sex ratios of the various sea turtle species in order to better predict how these will be affected by changes in nesting/incubation environments. Some possible ways that sea turtles may prevent extremely biased female sex ratios are by nesting earlier (cooler periods), nesting at higher latitudes (more north), changing the depth at which they bury their eggs, or changing the type of substrate they bury their eggs in (i.e. type of sand). That way more eggs will develop into males that might have otherwise been females (Fuentes 2011).
Just recently (August 18 2011), the first sea turtle nest was discovered in Delaware. Sea turtles are not known to nest that far north as well as that late in the season. They typically lay their nests on the coasts on South Carolina, Georgia and Florida. Alex Hoar, the U.S. Fish & Wildlife Service’s Northeast Endangered Species Coordinator said that, “And with global warming, events such as this may be a sign of what is to come” (Delaware Online).
Fuentes M.M.P.B, Limpus C.J., Hamann M. 2011. Vulnerability of sea turtle nesting grounds to climate change. Global Change Biology. 17(140-153)
Hawkes L.A., Broderick A.C., Godfre M.H, Godley B.J. 2007. Investigating the potential impacts of climate change on a marine turtle population. Global Change Biology: 13(923-932)
Spotila, James R. 2004. Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation. The Johns Hopkins University Press.
Sea turtle’s nest is so egg-citing: Sea turtle lays her eggs at Cape Henlopen in what may be the first such nesting herehttp://www.delawareonline.com/article/20110819/NEWS08/108190348/Sea-turtle-s-nest-egg-citing
Posted by Kristen S.
Kristen is a Fall, 2011 Intern at the National Marine Life Center. She recently graduated from U Mass Dartmouth with a degree in Marine Biology.