Global warming is altering marine ecosystems and sea turtles are being heavily affected with an increase in the average temperature of the earth’s surface. The sex of sea turtles is determined by the heat of the sand they incubate their eggs in. A warmer environment means more and more turtles are born female leading to a lopsided sex ratio within populations that could ultimately lead to their extinction.
Raine Island, Australia, reveals an unfolding crisis that is fast becoming a global problem. This is one of the planet’s largest and most important sea turtle rookeries where female turtles now outnumber males 116 to 1 - a discovery, which has shocked scientists worldwide. 200,000 turtles nest on Raine and the research by marine biologist Michael Jensen, Camryn Allen and Ian Bell has unearthed yet more unsettling truths. Sufficient data allowed scientists to determine the age of the turtles along this northern stretch of the Great Barrier Reef, where increasing heat has also lead to significant coral bleaching. Findings revealed that the ratio of females to males had grown more severe with time. Turtles that hatched there around the 1970s and 1980s were also mostly female, but only by a ratio of 6 to 1.
If turtle populations turn predominantly female, then there is the real risk that there will not be enough males to sustain populations. With so many turtle species already classified as either, vulnerable, endangered or critically endangered by the IUCN, if temperatures continue to rise the future of the sea turtle is far from certain.
Some reptiles such as sea turtles use incubation temperatures to determine the sex of their offspring. Females need warmer temperatures to develop. For example in green sea turtles, the temperature needs to be 31.1°C or above for the eggs to become female. Males will develop at the lower incubation temperature of approximately 27.7°C. Temperatures falling between the two will produce a mixture of male and female turtles. Heat produced by the eggs will also have an affect on sex determination as eggs at the centre of the nest will become predominantly female whilst those at the periphery Male. The point at which the sex of sea turtles is irreversibly determined is referred to as the temperature sensitive period, which typically spans the middle third of incubation.
Rising temperatures as a direct result of climate change will have significant consequences for all temperature dependant species around the world from alligators to iguanas and many fish found in estuaries and streams. Jensen says “temperatures are changing incredibly fast. Evolution requires many generations for animals to adapt. But turtles live for 50 years or more, and things are changing dramatically just in their lifetimes."
Since male sea turtles often mate with more than one female, and males usually mate more frequently, a minor female bias could be considered beneficial. A recent study of turtle rookeries around the world showed the ratio of females to males was roughly 3 to 1. In order to find out how much these figures have changed work needs to be done to assess the changing sex ratios of green sea turtles in other parts of the world.
Climate change also affects the nesting grounds of marine turtles. Rising sea levels flood nesting sites and drown the eggs. Beaches currently being used by turtles may vanish under the sea. The erosion of turtle nesting beaches also has an incredibly significant impact on populations. The erosion may produce cliff-like structures causing adult turtles to fall on to their backs and die unable to right themselves. 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). Marine turtles select their nesting sites based on low salinity, sufficient space above the tide line, adequate vegetation and high humidity; all of which may be affected by an increase in average global temperatures. Turtles are also at risk from logging as the absence of trees can’t provide sufficient shade to produce males.
It has been suggested that if there is warming of just a few degrees Celsius of average temperatures, an even more significant bias could occur. Such highly skewed sex ratios could potentially lead to population extinction resulting from decreased male recruitment. If temperatures climb too high the mortality rate of eggs will be devastating.
Camryn Allen emphasises that "the northern Great Barrier Reef is one of the largest genetically distinct populations of sea turtles in the world. What's really scary, though, is to think about applying this problem to populations where the numbers already are extremely low."
Did you know there are 7 species of sea turtle (via Conservation Status by IUCN)
1. Green turtle Endangered
2. Leatherback turtle Critcally Endagered
3. Hawksbill turtle Endangered
4. Flatback turtle (data sufficient)
5. Kemp’s Ridley turtle Critically Endangered
6. Olive turtle Vulnerable
7. Loggerhead turtle Endangered
We need to focus on educating the public on how to share beaches with turtles and what they can do to protect the species. When we collaborate and share this information it is brilliant for conservation.
Things you can do at home to help
Use reusable containers to avoid the single use plastics in food wrappers and plastic bags. Plastic bags look like jellyfish which is the staple diet of many turtes which will choke them.
Discontinue the use of q-tips and plastic straws, as plastic doesn’t ever disintegrate but merely break down in to microplastics.
Don’t release balloons as they can choke and strangle sea turtles.
Adopt a turtle nest through various schemes.
When on Sea Turtle beaches
Avoid taking chairs and cooler boxes as they can inadvertently crush nests
Dim mobile phones from dusk to dawn as artificial lights disorientate turtles and deter them from coming ashore to lay eggs
Choose watersports with care as turtles may be drawn to the sound of outboard motors and don’t see boats until it is too late
Don’t fish near nesting beaches or instead visit fish by snorkeling or scuba diving.