By Amruth Chinnappa
Humanity faces one of it’s biggest challenges in fighting global warming. It has directly and indirectly affected human life with sporadic climate changes resulting in the loss of life and property. While it can be explained as nature’s grotesque retaliation borne from the actions of man, other creatures often bear the brunt of its effects. As a result of global warming, more than 99 percent of newly hatched green sea turtles are now, female.
Green sea turtles do not develop gender-determining chromosomes as many other creatures do. The temperature of the egg’s environment determines the turtle’s gender. There exists what is known as a ‘Pivotal temperature’ at which there is almost an equal chance of a male or female hatching to be born. A few degrees higher leads to the birth of a female and if lower, a male is born. For these turtles, the pivotal temperature is exactly 29.3 degrees Celcius.
Conditions in the Great Barrier Reef
Temperatures in the Great Barrier Reef off the northern coast of Australia vary between 24 degrees Celcius to 32 degrees Celsius. Indelibly, the green sea turtle population presents a skewed gender ratio. For the past couple of years, it has been found that there are about 116 females for every male offspring. The effect of temperature on gender change was known before but this is the first time it has been recorded on such a large scale.
“This is extreme, like capital letters extreme, exclamation point extreme,” says turtle scientist Camryn Allen, of the National Oceanic and Atmospheric Administration in Hawaii. “We’re talking a handful of males to hundreds and hundreds of females. We were shocked.”
The species nests in only two regions, a collection of islands along the southern Barrier Reef and a small island named Raines toward the North. After their birth, the turtles mingle in the surrounding stretches of water and return to their respective islands to give birth. The research was undertaken by Michael Jensen, a research fellow with NOAA’s Southwest Fisheries Science Center in La Jolla, California. He aimed to find out the number of turtles belonging to each particular area by performing genetic tests. Yet, his demographic study lacked a vital part: the turtle’s sex.
Analysing the trend
A mature male turtle has a slightly longer tail compared to its female counterpart. However, it is impossible to determine the gender of turtles which haven’t reached maturity by everyday observation. The process involves an invasive method to check the animal’s gonads and was rejected for being impractical. Jensen worked with Allen, another marine researcher, and used the hormone levels present in a turtle’s blood to determine its species. The results of their study indicated that Raine island had been producing almost exclusively female turtles for the last 20 years. Previous records showed that the population of females was six times that of the males in the 1960s and indicates the rate of change in the phenomenon. Further validation was seen from the colder waters of the south, where the females outnumbered males just twice over.
“This combined with some neat modelling shows that cooler beaches in the south are still producing males, but that in the more tropical north, it’s almost entirely females hatching,” says Brendan Godley, a sea turtle expert and professor of conservation science at the University of Exeter.
Turtles have existed for a 100 million years and have seen the rise and fall of atmospheric temperatures. The present change, however, may be too fast for evolution to catch up. Female turtles occupy 87 percent of the total population till date but male turtles have a lot more sex than the females. So, researchers are not worried about any immediate consequence of the less gender ratio. The worrisome aspect involves the next generation which consists of more than 99 percent females while the global temperature does not show signs of reducing any time soon.
Necessity for sustained existence
Like a lot of nature’s inhabitants, turtles play an important role in the ocean’s ecosystem. They keep other populations in check and graze seagrass beds. A reduction in their population would have far-reaching effects on the ecological diversity as a whole. Along with green sea turtles, a number of other species are facing similar problems. The leatherbacks of Costa Rica and the Loggerheads of Florida have shown an increasing female bias.
Global warming aside, it is impossible to determine when the number of males is too low. It depends on a lot of local factors such as habitat change and human encroachment. Deforestation along the coasts have been identified to have reduced cool regions for nesting turtles. Further, poaching has taken its toll with turtle meat and eggs being popular among different communities. The study was conducted in a region with an abundance of turtles, disregarding their gender. The results show terrible consequences for smaller populations.
“The northern Great Barrier Reef is one of the largest genetically distinct populations of sea turtles in the world,” says Allen. “What’s really scary, though, is to think about applying this problem to populations where the numbers already are extremely low.“
Turtles are vital components of nature and hopefully, conservation efforts can help their continued existence.
Featured Image Source: Visual Hunt