 Every couple of years, during their breeding season, mature female sea turtles make their way out of the sea and onto dry land where they lay clutches of 50 to 350 eggs at a time and they do this in holes that they dig in the sand. After laying the nest, the female won't tend to it. The eggs are left alone to incubate for 50 to 60 days until they're ready to hatch. When they're ready to hatch, the eggs within a clutch hatch at around the same time and make a break for the sea across the sand, which leads to some spectacular sights which you've probably seen on your screen before. But there's something going on in those nests beneath the sand while the eggs are developing which we can't see but might be threatening the future of sea turtles as we speak. Sea turtles are some of the most beloved animals around the world and there are seven species of sea turtles around today. In the modern world they face an array of threats with all of the species able to be classified being labelled as between vulnerable and critically endangered on the IUCN red list for threatened species. You've probably already heard of some of the threats they're facing which include being unintentionally caught in fishing nets, postal development which leads to loss or degradation of suitable habitat, poaching and plastic pollution which can be mistaken for food. And there's one other that you've probably already thought of, climate change. But in order to understand a particular way that climate change is affecting sea turtles, we first got to take a look at their reproduction. In humans like in many other animals including other mammals, our biological sex is determined by a system called genetic dependent sexual determination. We have sex chromosomes which contain DNA that we inherit from our parents which determines our sex. Animals such as some tedious fish and reptiles including crocodilians and sea turtles display what is known as temperature dependent sexual determination where temperature experienced at certain stages in embryonic development determines the sex. There are different types of temperature dependent sexual determination but all we need to know here is that sea turtles are of type 1a and all this means is that above a certain temperature eggs hatch predominantly female and below a certain temperature eggs hatch predominantly male. The transitional temperature that produces 50% of each sex within a clutch is known as the pivotal temperature. This varies among species and populations but the difference between the temperatures that produce 100% females and 100% males is only a few degrees Celsius. It's easy to see how a change in temperature of just a few degrees Celsius could cause some real problems. With surface temperatures rising rapidly over recent decades and global average temperatures expected to rise by 2.6 degrees Celsius by 2100 there's a real risk that sea turtle populations could become extremely skewed towards females. And the bad news is we're already seeing this become a reality. We've known for decades that certain populations have been becoming increasingly female skewed but recent studies have actually found that certain populations are producing almost 100% females. A study by Jensen Etal published in Current Biology in 2018 looked at different populations of sea turtles along the Great Barrier Reef. They found that turtles coming from the cooler southern beaches had a female bias of around 69% whilst those coming from the warmer northern beaches had a female bias of up to 99.8%. What's even more surprising is that it's likely that this population has been producing primarily females for the past two decades and based on current climate change predictions they think that this population could become completely feminized. And what's more, similar trends have been found and similar predictions have been made about sea turtle populations around the world. At first you might think surely this is a good thing because more females means more eggs and more eggs means more offspring which obviously means greater population numbers which sounds pretty good for a species that's class is endangered but ultimately if populations aren't producing males there may not be enough if any males to sustain the population but there are ways that turtles could adapt to combat this. For instance they could change where they breed and where they nest or they could change when they nest to a cooler time of the year. The pivotal temperatures between producing males and females could change in response to increased temperatures and they could even start digging deeper holes for the nest which could provide cooler conditions the deeper down they go. The problem that they're going to face though is the fact that it takes them a long time to reach sexual maturity which in green sea turtles for example is around 25 years and another problem is the fact they display extreme natal homing. This is where they tend to go back to the beaches from where they hatched in order to lay their own eggs. Problems like these are going to make it very unlikely that they're going to start nesting in new areas and it's going to take at least centuries for adaptations to start showing up across generations. This means that they're going to be susceptible to the rapid climate change that we're expecting to see in the coming decades. But not all hope is lost just yet. Research into the effects of climate change on animals like sea turtles is still young and being developed. More studies will provide more data which will allow researchers to make more reliable and accurate predictions. There are also ways that we could intervene that have been suggested. One of the suggestions is simply planting trees along beaches which could provide shade and it could decrease temperatures by as much as 1.8 degrees celsius and of course there is the possibility that we tackle climate change head on before it impacts sea turtles so severely. The battle isn't over sea turtles are still here and we have the ability to make sure that it stays that way. Thanks for watching guys, really hope you enjoyed it. 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