Are Sea Turtles becoming a Girls Only Club?

Who remembers Crush and Squirt from Finding Nemo?  They were easily my favorite characters in the movie.  Crush and Squirt were Pacific Green Sea Turtles, an endangered species found in tropical and subtropical oceans worldwide.  The largest populations of these sea turtles are found in the Great Barrier Reef in Australia (surprise that’s what today’s post is about), and within the Caribbean Islands.  

Depending on their life stage, green sea turtles live in different habitat types.  They lay their eggs on beaches, and as they mature they spend their time in shallow, coastal waters.  Adult turtles spend their time in inshore bays, lagoons, and shoals.  They generally stay near continental and island coastlines, where they can be in protected shores and bays.

Life Cycle

So, female sea turtles lay their eggs on nesting beaches, usually in the tropics.  Within six weeks to two months, hatchlings make their way to the surface of the sand and into the water.  From there, they go through a life phase known as the “lost years”, where it is difficult to track their movements and actions. They return to coastal waters (growing a lot within that time), and continue to mature and forage near the bays.  Green Sea Turtles can reach sexual maturity between 10 and 50 years.  Most species of sea turtles nest about once every 2-4 years over the course of their lifetime, and only female sea turtles actually go ashore to lay the eggs.

 

Why am I telling you all of this?

Recently, it was found that the rising temperatures of the Great Barrier Reef  may be responsible for the feminization of green sea turtles.  Sea turtles are a species in which sex determination is temperature dependent.  Specifically, the sex is determined by the sand temperatures.  For this species, warmer sand dictates female turtles being born, while cooler temperatures give rise to male sea turtles.  It has been found that over the past two decades, temperatures of the sand in the Great Barrier Reef have increased to the point where it is virtually impossible for male sea turtles to be born.

Scientists have known for years that the sex ratio of sea turtles is dependent on the temperature, but this is one of the first times the effects of temperature has been documented across an entire species.  

The National Oceanic and Atmospheric Administration, California State University and the Worldwide Fund for Nature Australia published a paper in Current Biology that examined two populations of turtles on the reef.  They found that of the almost 200 thousand turtles of the northern group were almost entirely female.  Sea turtles from the warmer northern region of the Great Barrier Reef were showing that 99.1% of juveniles, 99.8% of subadults and 86.8% of adults were female.  That means that current sand temperatures have skewed the sex ratio to the point where there are almost no male sea turtles being born.  

Conservationists can hope for a few cooler years to produce a higher population of males, in general the average global temperature is said to increase by 2.6 degrees within the next 100 years.

 

What does this mean for the Green Sea Turtle Population?

Without either unnatural breeding or some form of cooling in the Northern population of the great barrier reef, we will begin to see larger declines in the sea turtle populations within the next few decades (a sea turtle can live up to a century).  On top of that, many of these sea turtles aren’t able to live their full life spans due to human intervention (chemicals in the water, poaching etc).

The research conducted and found also raise question to the effects of global temperatures on other species of marine turtles, and temperature dependent organisms.  In general, for the sea turtle population a female bias is good because most males mate with multiple females in one nesting season.  However, is a 99% bias too high?  Honestly, without substantial data, it is kind of unknown what effect the rising temperatures will have on the population in the long run.

But what are your thoughts?  Like I said, I think turtles are really cool, and their temperature dependent sex determination is only a small factor in why I think that way.  I like to look into the effects of the environment on populations because it’s really interesting to see how animals can adapt or sometimes migrate in order to suffice for their own needs.  I really can’t wait to see where this research goes, or how the population of green sea turtles will change over the next few years.  Anyways, see you all on Monday!

 

More information can be found at:

http://www.cell.com/current-biology/fulltext/S0960-9822(17)31539-7

https://www.theguardian.com/environment/2018/jan/08/great-barrier-reef-rising-temperatures-turning-green-sea-turtles-female

http://www.wwf.org.au/news/news/2017/chemicals-found-in-great-barrier-reef-green-turtles#gs.EWxwano

https://www.sciencedaily.com/releases/2018/01/180111101408.htm

https://news.nationalgeographic.com/2018/01/australia-green-sea-turtles-turning-female-climate-change-raine-island-sex-temperature/

http://www.seeturtles.org/sea-turtle-life-cycle/

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