Author: Barrett Benziger
When you picture where you might find a snake, a pile or rocks or a grassy field may come to mind, maybe even a tree if it is a tropical species. But how many people would picture a river, or a lake. That, however, is the preferred habitat for the Viperine snake, Natrix maura, which despite its name is not actually classified as a viper, a nonvenomous water snake native to Europe and Africa. Being a water snake, it primarily eats other aquatic organisms such as fish and frogs. While having an aquatic diet prevents it from competing with other terrestrial predators, it does pose some unique threats when it comes to human actions.
In disagreement with some people, heavy metal cannot cause you harm, however heavy metals can lead to a whole host of negative effects. More specifically the metal mercury, which is the metal affecting the Viperine snake. Mercury is a unique metal, as it is completely liquid at room temperatures, and while an incredibly interesting metal, it is one of the more dangerous ones. Exposure to mercury can cause birth defects and impaired brain function, as well a host of other nasty effects. (More information about the effects of mercury exposure can be found here).
You may have heard about mercury regarding seafood, as certain fish are unsafe to eat in larger quantities due to the risk of mercury poisoning. This happens as most organisms do not have a way to remove mercury from their tissues, and animals will absorb it throughout their lives, due to its presence in the environment or their food. Mercury ends up concentrating within the animal, this is then amplified for animals higher up in the food chain, as the amount of mercury they consume each meal will be higher, due to their consumption all the mercury their prey has ever absorbed alongside the prey itself. Therefore, many of the seafood with mercury warnings on them are predatory species, such as the tuna.
This means that any animal that primarily preys upon aquatic organisms, mainly fish, will on average have a higher risk of absorbing dangerous amounts of mercury than animals with a primarily terrestrial diet. And due to being a water snake, the Viperine snake fits that criteria. In a 2018 study, it was found that Viperine snakes that consumed mostly fish had much higher mercury concentrations within their body than those who consumed more ‘terrestrial’ prey, such as amphibians. The snakes found to have the highest mercury concentrations were those near a commercial fish farm. The fish at the farm were most likely fed food of a marine origin, where mercury concentrations are higher, causing the snakes that had preyed upon the farm to have the highest concentrations measured. This implies that commercial fish farming can lead to high concentrations of mercury moving inland into terrestrial environments. This could pose a large risk to the Viperine snake, as well as any animal that preys upon it.
As with most things involving conservation, there is more than one threat facing the Viperine snake. Besides rivers and lakes, they can be found in wetlands across their range. This causes problems when humans want to use those lands for agricultural purposes. Two studies have surveyed wetlands converted to agricultural fields, specifically rice terraces, within the snake’s range. The first had a 13-year window, the first survey in 1995 and the second in 2008. The survey found that the snakes had all but disappeared from the fields, only being found near the undeveloped areas. This fact helped inspire a second study at a similar location, with surveys in 2015 and 2018. This study was focused on the population structure in protected and unprotected habitats. They found that the snakes in the protected areas were on average older and larger than those in the unprotected regions.
This means that while the population is overall decreasing, protected areas can serve as refuges for the snakes, allowing them to grow larger and more mature, and avoid the risks from human activity within agricultural areas.
These studies reflect a large portion of the studies done on the conservation status of the Viperine snake, and it is currently not known if these problems are apparent throughout its entire range, or if they are isolated within these two agricultural areas. Further research is needed in this department. The influence climate change could have on this species has also not been fully researched, and it is not known to what extent it will affect the lives of these snakes.
If it is found that these problems are widespread, these studies have already shown some possible method for lessening the impacts humans are having on this species, such as the creation of protected areas within their ranges, as well as preventing mercury contamination of fish farms that the snakes have access to.
- “Health Effects of Exposures to Mercury” United States Environmental Protection Agency https://www.epa.gov/mercury/health-effects-exposures-mercury May 2021
- J. Lemaire, P. Bustamante,, A. Olivier, O. Lourdais, B.Michaud, A. Boissinot, P. Galan, F. Brischoux. Determinants of mercury contamination in viperine snakes, Natrix maura, in Western Europe. Science of the Total Environment. 635, 20-25 (2018).
- X. Santos, G.A. Llorente, Decline of a common reptile: case study of the viperine snake Natrix maura in a Mediterranea wetland. Acta Herpetologica. 4 161-169 (2009).
- R.M. Drechsler, P. Vera, D.C. Martinex, J.S. Monros. The effect of biological microreserves in a highly anthropized environment on the biology of Natrix maura (Linnaeus, 1758. Amphibian and Reptile Conservation. 14 64-72 (2020).
1. Christian Ferrer / Wikimedia Commons / CC BY-SA 4.0, https://commons.wikimedia.org/wiki/File:Natrix_maura,_Olargues_01.jpg
2. GNU Free Documentation License and CC BY 3.0, https://upload.wikimedia.org/wikipedia/commons/thumb/9/99/Pouring_liquid_mercury_bionerd.jpg/1024px-Pouring_liquid_mercury_bionerd.jpg
Author: Vanessa Morales
Even the largest hard shell turtles in the world can face problems bigger than themselves. With their population numbers already dwindling, ingesting metals may have the opposite effect of giving these endangered sea turtles an ironclad defense. But, how are these sea turtles getting their unlimited supply of metals in the first place? If green sea turtles are mainly herbivorous, how are metals a part of their food pyramid? It all starts with ocean pollution. But, before jumping into ocean pollution, we need to learn more about who these green sea turtles are.
As mentioned before green sea turtles, or Chelonia mydas, are the largest hard shell sea turtles in the world (1). These turtles can be found in two distinct populations, the Atlantic and Indo-Pacific. Even though they are found in two different populations, these turtles mainly stick to temperature and subtropical ocean waters. Weighing between 300-350 pounds and are about 3-4 feet long, it's hard to believe that a majority of their diet consists of sea grasses. In order to distinguish these gentle giants from other large sea turtles you can usually look at their coloration. Their shells are a dark brown color while their undersides are lighter ranging from a yellow white to a cream color (1). Their name and green pigmentation that can be found all over the turtle is attributed once again to their herbivorous diet (1). Along with their enormous size and weight, their life span is quite long, with some sea turtles living up to 70 years old. Within these 70 years of life they have multiple life stages that they undergo. These stages can be divided into a couple of categories: hatchling, juvenile, adult. In early development, hatchlings are found in shallower waters and only when they mature into juveniles do they depart into the open ocean. Hatchlings do not become juveniles until about 3 years old. Once they are juveniles they roam the open ocean but do not reach sexual maturity until about 20 years (1). When both males and females are adults, they will mate and the female turtles will return to nesting beaches every 2-5 years to lay about 110 eggs. Thus, the life cycle begins again. Even with their amazingly long life span and abundance of offspring, these green sea turtles are listed as endangered. There are many threats that these turtles face but their biggest one so far is ocean pollution.
Metal Pollutant Threat
With ocean pollution being one of the biggest threats this endangered sea turtle faces (1) there are many forms that this threat takes on. Whether it be ocean plastic debris, or liquid pollutants, the main one that we will be focusing on today is dumping of insecticides or other toxins containing metal pollutants in or near green sea turtle habitats. Most nesting beaches now have urbanization near and around them that has brought pollution closer to these fragile locations, through the use of insecticides (3). With chemical pollutants entering these habitats, these toxins are then taken in by other organisms such as plant life and other marine creatures (5). Since these metals are then found in plants and green sea turtles are herbivores, then they are inadvertently being exposed to these metals through their diet(4). Scientists over many years have been able to track the concentrations of specific metals in green sea turtles bodies, however, with green sea turtles being endangered, it is difficult to run specific tests on them since it causes an ethical/moral dilemma (2,3,4). What scientists have been able to conclude with the tests that they are able to run is that there are often high levels of heavy metals such as mercury, lead, and cadmium in the green sea turtles organ systems and blood (2,3,4). Another study even reported that there have been traces of these heavy metals found in hatchlings (4), indicating a jump start in these turtles' transformation into iron men. But, with further investigation, the effects of high concentrations of these toxins in the green sea turtle’s bodies is much more negative than granting them superpowers. Scientists have found correlations with higher levels of heavy metals leading to higher chances of the sea turtles having health concerns such as: shortened life span, birth defects, and issues with kidney and liver functions (2,3,4). These correlations haven’t been officially proven because of the limitations that scientists have on running experiments on this endangered species. What we know for certain is that our green gentle giants have had increased intakes of heavy metals in their bodies with each passing year (4).
So what can we do about this? How do we stop these sea turtles from dying out? It’s not too late to save these green sea turtles, conservation effects are already in place to help preserve these magnificent creatures alive. The lack of concrete knowledge only means that we need more scientists and activists involved in our scientific community to tackle problems such as this one. An easy thing to do is to get involved in environmental activism (6). By calling out bigger companies about their wasteful and destructive tendencies, we can help limit the amount of heavy metal pollutants that our marine life is being exposed to. Another way to get involved is to jump start a career in marine biology or other related fields of study, so you can be the next person involved in saving the sea turtles. There is so much you can do, all that it takes is the first step.
- Fisheries, N. (n.d.). Green turtle. Retrieved April 23, 2021, from https://www.fisheries.noaa.gov/species/green-turtle#overview
- Andreani, G., Santoro, M., Cottignoli, S., Fabbri, M., Carpenè, E., & Isani, G. (2008). Metal distribution and metallothionein In loggerhead (caretta CARETTA) and GREEN (Chelonia mydas) sea turtles. Science of The Total Environment, 390(1), 287-294. doi:10.1016/j.scitotenv.2007.09.014
- Godley, B. J., Thompson, D. R., & Furness, R. W. (1999). Do heavy metal Concentrations pose a threat to marine turtles from the Mediterranean sea? Marine Pollution Bulletin, 38(6), 497-502. doi:10.1016/s0025-326x(98)00184-2
- Komoroske, L. M., Lewison, R. L., Seminoff, J. A., Deheyn, D. D., & Dutton, P. H. (2011). Pollutants and the health of green sea turtles resident to an URBANIZED Estuary in San Diego, CA. Chemosphere, 84(5), 544-552. doi:10.1016/j.chemosphere.2011.04.023
- Ocean Health Index Chemical Pollutants http://www.oceanhealthindex.org/methodology/components/chemical-pollution
- Lauwrens, M. (2021) Seven Ways to Get Involved in Marine Conservation https://www.gviusa.com/blog/7-ways-can-help-save-worlds-oceans/
- Green Sea Turtle by Chris Neltner, CC BY-ND 2.0: https://www.flickr.com/photos/earthraceconservation/5576536635
- Large Banner Green Sea Turtle, Pixabay License: https://pixabay.com/photos/sea-turtle-green-sea-turtle-547163/
Author: Audrey Peshkam
As global temperatures rise higher and higher with each passing year, many organisms are at risk. One species that is especially vulnerable to climate change is the Leatherback sea turtle. They are the largest living species of sea turtle in the world, yet they face some of the most severe threats to rising environmental temperatures. This is due to a unique biological process they undergo that dictates the sex of their offspring: temperature-dependent sex determination (TSD). This aspect of Leatherback physiology makes it so that the temperature of their external environment determines whether or not the offspring will be born male or female. Typically, higher temperature ranges result in females while lower ranges result in males.
While TSD can be quite evolutionarily beneficial to Leatherbacks as well as a number of other organisms that also utilize this mechanism under normal circumstances, this has become a major concern for conservation biologists everywhere as climate change intensifies (3). The range of temperatures that determine sex in this species is very marginal, which essentially means that even slight fluctuations can have a huge impact (1). So as the sand on the beaches where these turtles lay their eggs only gets hotter, the more female hatchlings researchers will begin to see in Leatherback populations. While having more of one sex over the other doesn’t seem like such a bad thing, the problem is that temperatures are rising so high that the external temperature range is producing little to no males in some populations, putting a halt on the turtles’ ability to reproduce (1). Unfortunately, this means that if conservations and other environmentalists don’t step in to try to fix this problem, Leatherback sea turtles will eventually go extinct.
As we currently live through Earth’s sixth mass extinction, we may be becoming numb to the loss of yet another species. Though this animal may seem irrelevant and unimportant in the grand scheme of things, it’s important to understand that every organism has a place in its respective ecosystem. This becomes especially true when looking at the feeding habits of different organisms and how their actions impact entire food chains. Leatherback sea turtles feed almost exclusively on jellyfish. Because of this specialized diet, these turtles help to control the population levels of jellyfish, making them a keystone species or a species whose presence is critical to the health of its ecosystem. If there are fewer Leatherbacks, then this will result in there being more jellyfish. Though jellyfish are incredibly important to the oceans too, if their populations grow too large, then this will affect a number of smaller organisms that they feed on such as phytoplankton, zooplankton, and more. These much smaller species, especially phytoplankton, are necessary in maintaining the health of the world’s ocean, as they help regulate global nutrient cycles which help promote deep sea carbon sequestration. So the presence and ongoing survival of this single species of sea turtle can actually make a huge difference both locally and globally! Ecological examples like this continue to provide evidence of just how interconnected all organisms are, and why it is so crucial for us to protect all life on Earth.
Luckily, researchers have been studying the effects of climate change on TSD in this species as well as a number of others for decades now. Scientists were able to identify this as a potential issue as early as the 1990s and have been collecting data to find solutions ever since (1). Based on current research, what seems to be the most viable solution available for this species is clutch relocation (2). This is a fairly self-explanatory process, as it involves conservation biologists literally relocating groups of hatchlings. This can help regulate the sex ratios of Leatherback populations because by moving the eggs found in nests to shadier and cooler areas, conservation groups can actually help to produce more males since these shadier parts of the beaches tend to fall into the range of temperatures required to produced male offspring (2). However, researchers have warned about the potential dangers as well as limitations of this method (4). Firstly, the biggest concern is that sea turtle eggs are quite sensitive at this early stage in their life; therefore, relocating the clutches may actually create excessive disturbance and thus, may not produce as many healthy and viable hatchlings. The second concern is that if global temperatures continue to rise, then perhaps moving the clutches to cooler parts of the beach may not be enough to produce a sufficient number of males for the populations to persist, as even locations under shade may still be too hot for these turtles.
The ultimate solutions to this problem, as well as a number of other issues pertaining to the wellbeing of threatened species, will ultimately stem from large, institutional changes on a global scale. The current epoch in which we are living has been termed the “Anthropocene”: the age of humans. This is due to the immense impact that humans have had on our planet and how our activities are leading to irreversible changes in the natural world. However, many scholars challenge this term and instead choose to call this era the “Capitalocene”, thereby acknowledging the fact that not all human individuals have an equal impact in causing environmental destruction, but rather these horrific changes are a result of extractive capitalism. Large corporations contributing to greenhouse gas emissions from fossil fuel extraction, deforestation, and more are the true villains of our time, and in order to ameliorate our current climate situation, they will need to be held accountable by governments around the world. So while metal alternatives are obviously better, it’s not really our individual use of plastic straws that is killing the sea turtles, but rather greed and pollution on behalf of the world’s largest transnational corporations. Want to save the sea turtles? Get involved with an organization that holds the world’s largest polluters accountable, and don’t fall for the myths of buying your way to a sustainable lifestyle.
"A leatherback turtle hatchling stretching his legs. #animals #baby #turtle #babyanimals #wildlife #CostaRica #beach #conservation #volunteer #volunteerabroad #frontier #frontiervolunteers" by Frontierofficial is licensed with CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/
"Leatherback sea turtle/ Tinglar, USVI" by USFWS/Southeast is licensed with CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/
1. C.A. Binckley, J.R. Spotila, K.S. Wilson, F.V. Paladino. Sex Determination and Sex Ratios of Pacific Leatherback Turtles, Dermochelys coriacea. Copeia. 291 (1998). doi:10.2307/1447425
2. M.L. Rivas, N. Esteban, A. Marco. Potential male leatherback hatchlings exhibit higher fitness which might balance sea turtle sex ratios in the face of climate change. Climatic Change. 156, 1–14 (2019). doi:10.1007/s10584-019-02462-1
3. P. Santidrián Tomillo, M. Genovart, F.V. Paladino, J.R. Spotila, D. Oro. Climate change overruns resilience conferred by temperature-dependent sex determination in sea turtles and threatens their survival. 1-9 (2015). doi:10.1111/gcb.12918
4. P. Santidrián Tomillo, D. Oro, F.V. Paladino, R. Piedra, A.E. Sieg, J.R. Spotila. High beach temperatures increased female-biased primary sex ratios but reduced output of female hatchlings in the leatherback turtle. Biological Conservation. 176, 71–79 (2014). doi:10.1016/j.biocon.2014.05.011
Author: Faith Piercy
If you are ready to ride the surf and dive beneath the waves, then “gimme some fin… noggin’... dude”. If you know this quote off the top of your head, that means you have seen Finding Nemo. More specifically, I hope that you remember the green sea turtles that were traveling via the EAC. Green sea turtles are named after their green-colored fat, which they get from their herbivorous diet of seagrass and algae. Humans are one of the biggest culprits for causing problems for these turtles, thus leading to the decline of their populations worldwide. In order to prevent further decline, we need to be aware of how what we do affects the lives of these poor creatures. Understanding the impacts that humans have on this species, throughout their life cycle, is vital to preserving the ecosystems that they serve.
Why should we care about their populations?
If you have switched to using eco-friendly straws, then you might have seen the video of someone removing a straw from a sea turtle’s nose. This is just one out of many ways in which humans have a direct impact on sea turtle species. Green sea turtles are a keystone species in which they play an important role in ocean ecosystems by maintaining healthy seagrass beds and coral reefs, providing key habitats for other marine life, helping to balance marine food webs and facilitating nutrient cycling from water to land. Since they play such an important role to the ecosystem that they are a part of, watching their population levels is crucial to ensuring these habitats remain stable. As of 1978, green sea turtles are listed as an endangered species and the individuals that are left in the population are faced with many problems throughout their lifespan, specifically anthropogenic threats. Understanding the many impacts that humans have on this species, throughout their life cycle, is vital to preserving the ecosystems that they serve.
Making their way to the ocean
What came first, the turtle or the egg? We should simply begin with the egg. A female will lay her eggs, cover them with sand, and then return to the ocean. Meanwhile, the eggs have an incubation period of about two months. When it is time for the eggs to hatch, which is typically at night, they collectively push the sand down so they can all successfully merge out to the surface of the beach. Once they are out of the nest, the hatchlings go through a 24 hour frenzy period where they must make their way to the ocean by crawling from their nest across the sand. Hatchlings have an innate instinct that leads them in the brightest direction, which is normally the moonlight that reflects off of the ocean. During this frenzy, these turtles are subject to natural predation, thermal stress and dehydration. With the urbanization of beaches, light levels have increased causing the hatchlings to become disoriented. This disturbance makes it so that these baby turtles are on land for a longer period of time, thus increasing their exposure to what was mentioned earlier (5).You can read more about the impacts that crawling has on hatchlings here. If they are lucky enough to make it past this stage in their lives, then they must face the next set of challenges.
Watch your head little one
A major challenge that juvenile turtles face is the presence of boats in shallow waters. Green sea turtles need to come to the surface in order to breathe. So when they come to the surface for air, they are more likely to get hit by a boat, especially when they are juveniles because more boats are present in shallower waters. Propeller and collision injuries from boats are not uncommon and these types of injuries are more frequent in areas with a high level of recreational boating. If the sea turtle gets brain damage from the collision, it won’t be able to do normal behaviors such as feeding or evading predators (1). The anthropogenic presence of boats have significant impacts to turtles in the juvenile stage of life and this can cut the numbers of sea turtles present in our oceans even further.
Adulting is overrated
The threats that are associated with the presence of humans do not go away once turtles reach adulthood. At this point, turtles are faced with problems such as pollutants and marine debris.
Coastal development contributes to the pollution of sea turtle habitat from runoff and wastewater discharge (4). Additional chemical exposure that humans have put into the environment can also cause abnormalities in embryonic development, disrupt endocrine balance, and alter important metabolic functions (4).
When you have walked along the beach, have you ever noticed how much trash is laying around? Over 8 million tons of marine debris enter the oceans annually from both ocean and land sources (2). A majority of the trash and debris that covers our beaches comes from storm drains and sewers, as well as from shoreline and recreational activities such as picnicking and beachgoing. Abandoned or discarded fishing gear is also a major problem because this trash can entangle, injure, maim, and drown marine wildlife and damage property. Green sea turtles interact with considerable quantities of marine debris, most specifically plastics, which have both lethal and sub-lethal effects (2). Both of these anthropogenic contributions to the marine environment can cause many detrimental effects to an already small population.
Finding the right nesting place
Scientists have uncovered that turtles return to the same place every year to lay their eggs by sensing the specific magnetic field of the beach where they were born. Each beach has a distinct magnetic pattern which becomes imprinted on a turtle's brain to help them find their way back to that particular beach. It has been determined by research that the number of green sea turtle nests is positively correlated with the presence of vegetation on the beach and negatively associated with the presence of predators such as dogs, seabirds, raccoons, and ghost crabs. Females select where to lay their eggs based on the slope of the beach. Flat beaches have lower nesting density whereas beaches with a median slope is preferred (3). This is likely due to flat beaches lacking protection from the tides and a beach that is somewhat sloped is still easy enough for the females to make their way up the beach without exerting an abundance of energy. However, with urbanization, coastal development, vehicle traffic on beaches, and other human activities could alter the layout of a beach to render a location unsuitable for females wanting to lay their eggs. The female turtle will then have to find a new nesting ground.
To wrap things up
Green sea turtles have been living and thriving in the world’s oceans for 150 million years and yet they are now in danger of extinction largely because of changes brought about by humans. So what can you do? You can reduce the amount of marine debris in our oceans by reducing the amount of plastic you use; this includes using reusable water bottles and shopping bags. You can also participate in your local coastal clean-up events to help keep our beaches clean. When you happen to see a sea turtle while you are at the beach, remember to keep your distance so that you don’t disturb nesting females, nests, or hatchlings. If you live in an area where it is known to be near a nesting beach, try to keep nesting beaches dark and safe at night. Lastly, If you see a stranded, injured, or entangled sea turtle, contact professional responders and scientists who can take appropriate action. Numerous organizations around the country are trained and ready to respond.
Keystone species, incubation period, marine debris, magnetic field
- D. W., Goldberg, A., Adeodato, D. T., Almeida, L .G., Correa, J., Wanderlinde, Green turtle head trauma with intracerebral hemorrhage: Image diagnosis and treatment [WWW Document], (2010).
- F., Yaghmour, M., Al Bousi, B., Whittington-Jones, J., Pereira, S., García-Nuñez, J., Budd, Marine debris ingestion of green sea turtles, Chelonia mydas, (Linnaeus, 1758) from the eastern coast of the United Arab Emirates. Marine Pollution Bulletin 135, 55–61, (2018).
- I. S., Siqueira-Silva, M. O., Arantes, C.W., Hackradt, A., Schiavetti, Environmental and anthropogenic factors affecting nesting site selection by sea turtles. Marine Environmental Research 162, 105090 (2020).
- L. M., Komoroske, R. L., Lewison, J. A., Seminoff, D. D., Deheyn, P. H., Dutton, Pollutants and the health of green sea turtles resident to an urbanized estuary in San Diego, CA. Chemosphere 84, 544–552 (2011).
- Pankaew, K., Pankaew, S.L., Milton, The effects of extended crawling on the physiology and swim performance of loggerhead and green sea turtle hatchlings. J Exp Biol 221, jeb165225, (2018).
"Green-Turtle_Projeto_Tamar_1" by Oregon State University is licensed with CC BY-SA 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/2.0/
"Entangled green sea turtle" by NOAA Marine Debris Program is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/
Author: Rachael Alcala
Sea Turtles are often associated with good luck and endurance; these are some of the same attributes they will need in these coming years. Since the 20th century, global and sea temperatures have been on the rise due to climate change, with an expectation to increase by 5 degrees celsius by 2100 (5). Chelonia Mydas, otherwise known as the green sea turtle, are expected to take a major hit to their population as a result of these rising temperatures. Hatchlings, or baby sea turtles, sex is determined by nest temperature. A warmer nest temperature means more females and cooler temperature means more males (2). As this warming continues, there is a good chance that 100% of future hatchlings born will be females (4). You might be thinking, how is this a bad thing? That’s a great question. Sure, a sudden boost in females has the potential to bump population numbers, but this would only be temporary. In reality, they would still be reliant on male sea turtle availability (3). Without enough male sea turtles, there is a high risk of population loss faced by these ancient creatures. However, there is light at the end of the tunnel. In combination with lowering CO2 emissions, green sea turtles can make major evolutionary adaptations to come back from this setback.
As of now, there doesn’t seem to be any sign of climate change slowing down. Right now, a lot rests in the flippers of green sea turtles. A possible solution comes from these evolutionary adaptations. Studies have shown that sea turtles have a genetic basis for selecting microhabitat nesting characteristics (3). Micro-what? Trust me, I’m thinking the same thing. Microhabitat nesting characteristics refer to characteristics sea turtles look for when preparing to lay their eggs. Some characteristics include nest shade, nest depth, or nesting beach (1). More on these nest characteristics can be found here. There’s no “right” nest per se, sea turtles just dig what feels right. Their nesting behavior really depends on their location and the species type (6). However, by adapting some of these nesting behaviors, there is a better chance that their nests can become cooler and lower the amount of female hatchlings (1).
Looking deeper into the ways they can alter their nesting behaviors, we will first turn our attention to nest depth. By making their nests deeper than the typical 30-90 cm, the nests have less of a temperature fluctuation and are overall likely to become cooler(1). The same outcome will occur through adjusting nest shade. Shading the nest in areas of vegetation, such as near bushes or under trees, will help make the nest on average 1 degree celsius cooler (1). In fact, it was found that nests made in the open sand were found to produce a larger number of females compared to nests made in more forested areas(3). To learn more about the benefits of vegetation for nesting sites, you can visit here. Nesting beaches are a little bit more difficult to work around. After hatching, green sea turtles spend their juvenile years living in the open ocean, and once they become adults they will migrate from coastal areas where they forage to the beach they originally hatched in order to reproduce. It is an innate ability, something they are born with, to return to the beach where they are born to lay their eggs. Future generations are dependent on this generation to nest on beaches where they are not at risk of overheating or land erosion (6).
So changing their nest is all they need to do? That’s definitely one of the ways they can deal with their dilemma. Another way is through thermal tolerance. Thermal tolerance is essentially how much heat that can be endured by the green sea turtles; it varies among sea turtle species and also has a genetic basis (4). If green sea turtles are able to adjust their body temperatures and adapt to local thermal conditions, they are likely to pass this adaptation onto further generations. This idea suggests that if hatchlings are born at high nest temperatures, they can transfer this tolerance onto the next generation, increasing their overall fitness and increasing their chances of survival (3).
The overall consensus seen in studies is that by altering nesting characteristics and adapting thermal tolerance, there is a high chance that green sea turtles can limit the number of female hatchlings produced in the face of climate change. There you go, problem solved! Easy peasy right? Well, yes and no. Green sea turtles are found all over the world in the temperate and subtropical waters of the Atlantic, Pacific, and Indian Ocean and the Mediterranean Sea. Hypothetically speaking, they have a choice of any beach in the world to choose from to make their nests, but it’s not that easy. They live quite a long time, with a lifespan of about 70 years or more. However, they don’t reach sexual maturity until they are about 25-30 years old. With the implications of climate change creeping upon us, it is important that these adaptations are made sooner rather than later.
Where do we go from here? There is still a lot we need to figure out before we can make any final conclusions. For starters, temperature has been found to be the main driving force behind sex determination in sea turtles, however studies have present other potential influential factors like nest moisture (4). Additionally, there is much to be learned about male sea turtle breeding behaviors, which would be helpful in having a better understanding if current populations can possibly be stabilized through these climate changes (2). Other areas that are lacking include inbreeding or small green sea turtle populations that could lower genetic variation or evolutionary adaptations in the species (1). We also don’t really know how green sea turtles will react to other effects that come with climate change such as rain storms, changing currents, rising sea levels, and ocean acidification. With so much unknown, it is far too early to assume the worst.
The biggest thing we can do to help these shelltastic beauties is to do our part in lowering CO2 emissions. This sounds like a big task, I know, but really the best and easiest way to be involved is to stay informed. You can visit here to find easy ways to reduce your carbon output. To learn more about current and future climate change trends go here. If you’d like to learn more about our green buddies you can visit here. These resilient creatures have endured so much already, they surely have luck on their side.
“A green sea turtle at Maui” by Bernard Spragg licensed under CC0, https://www.flickr.com/photos/volvob12b/17177571549/
Meme made by Rachael Alcala
- J. Blechschmidt, M. J. Wittmann , C. Blüml, Climate change and green sea turtle sex ratio—preventing possible extinction. Genes. 11(5), 588 (2020).
- J.O. Laloë , J. N. Tedeschi, D. T. Booth, I. Bell, A. Dunstan, R.D. Reina, G.C. Hays, Extreme rainfall events and cooling of sea turtle clutches: implications in the face of climate warming. Ecol Evol. 11: 560–565 (2021).
- A.R. Patrício, M.R. Varela, C. Barbosa, A.C. Broderick, P. Catry, L.A. Hawkes, A. Regalla, B.J. Godley, Climate change resilience of a globally important sea turtle nesting population. Glob Change Biol. 25: 522– 535 (2019).
- P. Santidrián, J. R. Spotila, Temperature‐dependent sex determination in sea turtles in the context of climate change: uncovering the adaptive significance. BioEssays 42(11), 2000146 (2020).
- J.L. Stubbs, N. Marn, M.A. Vanderklift, S. Fossette, N.J. Mitchell, Simulated growth and reproduction of green turtles (Chelonia mydas) under climate change and marine heatwave scenarios. Ecological Modelling. 43, 1109185 (2020).
- M.Y. Rumaida, S.A. Putra, A. Mulyadi, S. Nasution, Nesting habitat characteristics of green sea turtle (Chelonia mydas) in the Tambelan archipelago, Indonesia. J Coast Conserv. 25, 6 (2021).
Authors: Chloe Reilly, Hannah Thacker, Jonathan Phu, Richard Urbina
As a society, we have a grim awareness of the problems facing life in our oceans. One issue that many people are familiar with is bycatch, the accidental capture of animals who were not the original targets of fisheries. In many cases sea turtles die when they are entangled in nets. Some lucky animals are rescued and released. However what people, including scientists, don’t fully understand, is whether sea turtles who are rescued end up living healthy lives after they are released. Society’s knowledge on this subject is limited but sea turtles, including the endangered loggerhead and leatherback sea turtles, have been giving us clues to discover how they are faring and it is our time to investigate. These clues can be found in their “physiology”, the study of how the organism’s body functions. But before we jump into the physiological clues sea turtles are leaving us, here are some facts about the species of interest.
Both Loggerhead (Dermochelys coriacea) and Leatherback sea turtles (Caretta caretta) are found around the world in all of the major oceans. While having such a huge range can be perceived as a positive thing, some might also argue that this increases their chance of run-ins with fishing gear. Healthy Leatherbacks and Loggerheads can be anywhere from 3 - 6.5 feet long and weigh up to 2000 lbs (with Loggerheads landing on the lower spectrum) (1,2). While both species of turtles face similar anthropogenic (human caused) effects, their physical characteristics are actually quite different. Leatherbacks are unique in that they lack an external hard shell and instead have a shell covered with a thick layer of leathery, dark skin (3). Loggerheads, on the other hand, have the typical tortoise-shell coloration on their shell and greenish yellow skin on their heads and limbs (4). Many of their unique characteristics influence how their physiology is affected by net entanglement.
To help sea turtles survive entanglement, we first need to understand exactly what they are facing. Luckily for us, scientists have been doing some sleuthing. Fisheries around the world use a variety of techniques to fish and it turns out that each of methods poses a distinct set of problems.
One example is pelagic longline fishing. When caught on one of these longlines the sea turtles are usually able to reach the surface to breathe. Williard et al. found that loggerhead sea turtles tangled in longlines have only low levels of lactate (5). If a turtle is stuck underwater, they are unable to breathe. Low levels of lactate show that they are using anaerobic metabolism and other processes to compensate for awhile until they are able to surface and breathe normally. However longline fishing is not without issues! Crognale et al. described how longline fisheries use chemiluminescent lights to attract swordfish, but sadly leatherback turtles are also drawn to these lights (6). If we are able to release them quickly enough, these leatherbacks may survive but it is still very worrisome that the lights are attracting them to a source of danger.
Other types of fisheries are also hazardous to sea turtles. In fisheries that use submerged nets, turtles are likely to become severely entangled and be stuck underwater, unable to surface. García-Párraga et al. discovered that sea turtles captured by submerged nets display the symptoms of decompression sickness and are likely to pass away from this, even if they are released from the net itself (7). Now that we are familiar with the victims and suspects keep reading to find out about the trail of physiological clues scientists are finding!
What clues do blood analyses give us about the effects of bycatch?
In order to understand how turtle entanglement affects their physiology, many researchers have looked to blood work to unravel the mystery surrounding bycatch. A recent study by Hunt et al. investigated how entanglement is linked to stress effects in Leatherback turtles. Interestingly, blood analyses found that when Leatherbacks are trapped in fishing nets, stress hormones like corticosterone and thyroxine dramatically increase (8). According to Williard et al., this is actually beneficial to the turtles in the short term because these hormones induce a “fight or flight” response to redirect energy towards life preservation (5). Unfortunately, if turtles are entangled for too long, these stress hormones could become permanently elevated, which poses threats by taking energy away from important bodily processes. In many cases of turtle entanglement, individuals are not able to escape the nets in time and often die from the negative long-term effects. With all of the negative effects of bycatch, the future of turtle populations may seem grim. On the bright side, many of our world’s brightest scientists and turtle enthusiasts alike are working diligently to crack the code on this turtle mystery and save lives worldwide.
Help Needed to Solve the Case!
Now that we have discussed the issues these sea turtles have encountered through accidental bycatch by longline fisheries, potential solutions have been brought up in protecting this endangered species. On the bright side, scientists are actively researching ways for fisheries to be proactive in protecting sea turtles. By changing the types of light on swordfish nets we would be able to prevent Leatherbacks from being attracted to and caught in the nets. So far, people have been releasing these turtles back in the ocean thinking the sea turtle is relaxed which isn’t true. The sea turtles may be in shock from being entangled in a net even just for a few minutes. Solutions proposed by Williard et al. explain that in order for us to protect sea turtle deaths from post release, we must study the signs of a stressed turtle (5). If the turtle is conscious enough, releasing them right after they are caught will help avoid injuries to the sea turtles. Stressed sea turtles should be kept dry and under shade for amount of time to recover their regulatory movements. Learning these signs of sea turtles would help protect sea turtles from death at most costs. The future of our shelled friends will rely on the hands of humans if they are accidentally caught in nets not intended for them. Turtle enthusiasts across the world can join the movement and help prevent future sea turtle catastrophes.They can help donate to The State of the World’s Sea Turtles (SWOT) with everyone’s help they can research more ways to help sea turtles. There are also opportunities to volunteer with sea turtle conservation groups to get hands on experience! Just be sure to do your research and pick an organization with values you agree with!
Photograph of Loggerhead and Leatherback turtles were retrieved from https://upload.wikimedia.org/wikipedia/commons/1/13/Loggerhead_turtle.jpg and https://commons.wikimedia.org/wiki/File:Leatherback_sea_turtle_from_flickr.jpg respectively.
Photograph of longline fishing gear retrieved from https://commons.wikimedia.org/wiki/File:Mediterran_fishing_gear.jpg
- J.Y. Georges, S. Fossette, Estimating body mass in leatherback turtles Dermochelys coriacea. Mar Ecol Prog Ser. 318, 255-262 (2006)
- C.K. Dodd, Synopsis of the Biological Data on the Loggerhead Sea Turtle Caretta Caretta (Linnaeus 1758). (No. FWS-88(14)).
- H. Chen, W. Yang, M. Meyers, Leatherback sea turtle shell: A tough and flexible biological design. Acta Biomaterialia. 28, 2-12 (2015).
- P.T. Plotkin, M. K. Wicksten, A.F. Amos, Feeding ecology of the loggerhead sea turtle Caretta caretta in the Northwestern Gulf of Mexico. Marine Biology, 1, 1–5. (1993)
- A. Williard, M. Parga, R. Sagarminaga, Y. Swimmer, Physiological ramifications for loggerhead turtles captured in pelagic longlines. Biology Letters. 11, 1-5 (2015)
- M. A. Crognale, S. A. Eckert, D. H. Levenson, C. A. Harms, Leatherback sea turtle Dermochelys coriacea visual capacities and potential reduction of bycatch by pelagic longline fisheries. Endangered Species Research. 5, 249-256 (2008)
- D. García-Párraga, J. L. Crespo-Picazo, Y. Bernaldo de Quirós, V. Cervera, L. Martí-Bonmati, J. Díaz-Delgado, M. Arbelo, M. J. Moore, P. D. Jepson, A. Fernández, Decompression sickness (‘the bends’) in sea turtles. Diseases of Aquatic Organisms. 111 191-205 (2014)
- K. Hunt, C. Innis, C. Merigo, R. Rolland, Endocrine responses to diverse stressors of capture, entanglement, and stranding in leatherback turtles (Dermochelys coriacea). 4, 1-12 (2016)
Authors: Jillian Petersen, Mary Gomes, Rachel Sequeira, Vanessa Orozco
Are you feeling the temperature rising? Because leatherback turtles are! Do you see that adorable little baby leatherback sea turtle (Dermochelys coriacea) up above? Well, we have some bad news… they are negatively affected by current rising temperatures — a result of climate change. The detrimental effects this species is facing is not just limited to its babies, but also adult leatherback turtles. Rising atmospheric and sea temperatures are affecting all aspects of this turtle’s life history — from hatching success to its hunting ranges.
Because leatherback sea turtles are reptiles, they depend on sunlight for warmth. This kind of animal is referred to as an ectothermic conformer. Baby leatherback turtles’ likelihood to emerge and flourish is really dictated by the environmental temperature that they are surrounded with in their home nest. Just like people prepare for a baby to come home by building them the most sturdy cribs, sea turtle mommas come ashore and lovingly dig a nest along the sandy beaches. The depth of the nest provides protection against temperature fluctuations since the newly laid eggs are very sensitive to heat (1). Leatherbacks turtles eggs are more vulnerable to small changes in temperature because the mothers tend to dig a deeper, bigger nest which eliminates the eggs’ need to defend against naturally occurring temperature changes (1). As rapid climate change drives temperatures to new heights, leatherback eggs are in hot water. Sudden spikes in temperatures cause a higher death rate of these precious embryos. Looking into how sensitive populations, like these sweet babies, respond to temperature increases helps us determine how to approach these types of issues in the future— but it doesn’t end there.
Sea turtles are extra special reptiles because they rely on temperature-dependent sex determination (TSD), which means that if the temperature is hot, they have more female offspring, and if it’s cooler, they have more male offspring (2). Since the temperatures around the globe are changing due to climate change, there’s been a whole lot of female turtles hatching, which isn’t necessarily a good thing. Drastically skewed sex ratios can lead to too many female turtles and too few male turtles. This is very worrisome — an imbalance like this could affect the entire leatherback turtle population. Not only do leatherback have to worry about their TSD, they also have to mind their DNA!
These majestic turtles are getting sick, and it’s not from the flu. When the ocean gets warmer, certain deadly chemicals start to build up in the water. The leatherback turtles absorb these chemicals like sponges and their health declines because of the toxicity. One chemical that is showing up due to rising temperatures is called hexavalent chromium and attacks the turtles’ lung cells and even their DNA, making it hard for the turtles to survive and reproduce (3). If temperature continues to rise, the accumulation of more and more toxins, like this one, is bound to have a negative effect on our friends in the ocean. We can lend a flipper to these turtles (and all that call the ocean home for that matter!) through preventative action, like programs to study and research the connection between temperature and the rise of chemicals that can affect all marine animals.
Fun fact! Did you know that leatherback turtles actually have the largest foraging range in both tropical and temperate areas when compared to other reptiles (4)? As previously mentioned, leatherbacks are animals that rely on external temperature to heat their bodies. Lucky, they are so big that they can retain heat better than other reptiles, allowing them to have such large ranges. They are so good at this that they have an astounding core temperature of 25°C (4)! The turtles’ ability to maintain these large ranges is amazing, but research suggests that as sea temperatures continue to rise, their foraging ranges will be forced to widen even more — maybe past a sustainable point (5). For now, there is little research that investigates exactly how expanded ranges will affect the leatherbacks’ body makeup, overall health, and impact on the environment.
Leatherback turtles are one of many of nature’s many beautiful, yet endangered species. With their population number on the decline, these turtles are in dire need of change — and not the temperature change they have been experiencing. The negative effects on this species in every stage of its life are in many caused by our own human impact. Although human interference is what got leatherbacks into this mess, human interference is just what they need to get out of it. By researching deeper into how climate change affects leatherback sea turtles, we get a peek into the future of not just these special turtles, but all sea creatures alike. With progressive action in this field, we can answer questions that need to be addressed and find solutions to issues that plague the animals in the world all around us.
Want to learn more?
Here are some more fantastic journals about leatherbacks:
Research into Leatherbacks
Browse open access environmental journals
- S. P. Tomillo, M. Genovart, F. V. Paladino, J. R. Spotila, D. Oro, Climate change overruns resilience conferred by temperature-dependent sex determination in sea turtles and threatens their survival. Global Change Biology. 21, 2980-2988 (2015).
- C. Binckley, J. R. Spotila, K. Wilson, F. V. Paladino, Sex determination and sex ratios of Pacific leatherback turtles, Dermochelys coriacea. Copeia. 2, 291-300 (1998).
- J. Davenport, Temperature and the life-history strategies of sea turtles. Thermal Biology. 22, 479-488 (1997).
- R. M. Speer, C. F. Wise, J. L. Young, A. M. Aboueissa, M. Martin Bras, M. Barandiaran, E. Bermúdez, L. Márquez-D'Acunti, J. P. Wise, The cytotoxicity and genotoxicity of particulate and soluble hexavalent chromium in leatherback sea turtle lung cells. Aquatic Toxicology. 198,149-157 (2018).
- M.C. James, J. Davenport, G. C. Hays, Expanded thermal niche for a diving vertebrate: a leatherback turtle diving into near-freezing water. Experimental Marine Biology and Ecology. 335, 221–226 (2006).
Authors: Elaina Noble, Christina Rockrise, Jordan Bakhtegan, Jonathan Flores
Imagine if every person born in the fall and winter months were born male, while everyone born in the spring and summer months were born female. For the painted turtle, a widespread species of freshwater turtle, this is the reality. The sex of the painted turtle, or Chrysemys picta, is determined by the temperature of the environment during its development. When incubated in warmer temperatures, the eggs develop into female turtles, while in cold temperatures the eggs develop into males.
Based on the season you were born in, what gender turtle would you be?
Chrysemys picta is a species of reptile that is native to North America(1). These little turtles have a dark shell with red and yellow markings on their underside, head, legs, and tail(2,3). They spend their time in the water of slow-moving streams or basking on nearby rocks(4). Painted turtles are extraordinary at holding their breath and are known to be very tolerant of cold temperatures as adults. They are able to hibernate underwater or in mud during the winter for months on end. To do this they make energy at a slower rate without the use of oxygen in a chemical process known as anaerobic respiration. If humans were to do this, the chemical byproducts would build up to toxic levels. The turtles, however, are able to take the toxins up into their shell and therefore can tolerate much higher levels of these toxins.
There are four subspecies of painted turtle, all of which enjoy different diets depending on their habitat(6). Western (C.p. bellii) and Southern (C.p dorsalis) painted turtles enjoy both plants and animals in their diet(7,8). Eastern (C.p.picta) turtles prefer fish and Midland (C.p. marginata) turtles feed on a variety of insects(7,8). Between March and mid-June, the turtles swim to deeper parts of their home stream to breed. Between May and July, females leave the water, travelling anywhere from a few yards to a half a mile to dig a hole and lay up to 11 eggs, after which she returns to the water. After about 72 days, typically in the late summer, hatchlings begin to emerge and head straight for the water. Both the eggs and the hatchlings are extremely vulnerable to prey, with only about 10% surviving to adulthood(9).
While these creatures are known to be relatively resilient as adults, warming temperatures pose a threat for them during early development. Two studies, one by Fredric J. Janzen, and one by Fredric J. Janzen and Lisa E. Schwanz, explored the way in which rising temperatures may have a negative impact on the long term survival of this species. Unlike humans where sex is determined genetically upon fertilization of an egg, turtles rely on environmental temperature to switch on the developmental process of either male or female traits during incubation(10). In warmer temperatures, this process results in female turtles while cooler temperatures give rise to male turtles(10). Temperature changes as little at 1℃ (1.8°F ) can significantly alter the sex ratio of nests(10).
Current climate change models project temperatures to rise 1.67 °C to 6.67 °C (3 °F to 12 °F) worldwide by the year 2100 (13). Seeing as how warmer temperatures during incubation result in the development of female turtles, this shift towards a warmer climate could lead to an increased number of females hatching out of nests compared to males(10,11). This kind of unbalanced sex ratio is already being seen in the wild. An excess number of females paired with a shortage of males would result in decreased reproductive success and an overall decrease in the number of these turtles in the wild. This issue is made worse by the females’ polyandrous lifestyles, meaning that they will mate with multiple males during the mating season(12). In theory this allows for greater genetic diversity that protects the population against environmental changes by allowing for adaptive change. These female painted turtles then store the sperm of multiple males which allows for sperm competition, in which the sperm from all of the males attempt to compete with each other to fertilize the eggs. This means that hatchlings from a single nest may have several different fathers, thus increasing the genetic diversity. However, if there are less males to mate with, the diversity level could plummet, giving the species even less of a chance to survive in rapidly changing environments. When diversity is reduced, a single type of environmental disturbance is more likely to negatively affect the survival and reproduction of all viable offspring.
Sex ratios are not the only threat that this species faces due to climate warming. In a paper by Telemoco et al. (2013) titled Extreme developmental temperatures result in morphological abnormalities in painted turtles (Chrysemys picta): a climate change perspective, environmental temperatures higher than 34 °C (93.2 °F) were shown to cause deformities in the scutes, the individual bony plates that make up the shell, of hatchling Chrysemys picta (14). These scute deformities seemed to result in lower survival and reproductive rates in the adult Chrysemys picta in comparison to the normal turtles. A higher rate of scute deformities could cause the population numbers of the painted turtle to drop. However, more studies are needed to find the physiological link between scute deformities and exactly why it lowers their ability to survive.
Unfortunately, researchers believe that turtles will be unable to adapt to the 3°C (37.4°F) rise in temperatures set to occur in the next 100 years. Climate change is happening at a faster pace than the turtles can evolve11. However, more research focusing on microhabitats and nesting site choice could help us understand how these organisms might be compensating for this drastic temperature change. Microhabitats are small areas that exhibit a miniature climate which is different from the surrounding area, such as a shaded area under a bush where temperatures may be cooler. It is still uncertain what factors affect the selection of a nesting site location. We may find that turtles, over time, will adapt to prefer cooler microhabitats for their nesting. This may help to combat the challenges of unbalanced sex ratios and scute deformaties, which would be otherwise intensified by climate change. Additionally, studies are needed on temperature tolerance. The Telemoco et al. (2013) study showed that some individuals had higher heat tolerance than others during development and were born without scute deformities even when exposed to high temperatures during incubation. It is unknown, though, whether this trait can be passed down to offspring. If so, this may prove yet another way the turtles can adapt over time to overcome these rising temperatures and their effects on development.
While the future may seem bleak for these turtles, continued research and conservation will help us to learn more about these little reptiles so that we can help maintain Painted Turtle populations for as long as possible. Of course, doing your part to reduce carbon emissions is significant, however, conserving energy and reducing waste are only helpful when we can all come together to make a difference. Helping to educate the public on the many ways climate change could affect the animals in our own ponds and backyards is an important step to forming a community of change. If you have painted turtles in your area, you can educate the public or participate in local discussions that affect their habitat in nesting sites as well as encouraging their preservation.
- C.H. Ernst, and J.E. Lovich, “Chrysemys picta, Painted turtles” in Turtles of the United States and Canada, C.H. Ernst, J.E. Lovich, Eds. (Johns Hopkins University Press, USA., 2009). Pp. 183–2112.
- J.E. Steffen, et. al., Carotenoid composition of colorful body stripes and patches in the painted turtle (Chrysemys picta) and red-eared slider (Trachemys scripta). Chelonian Conservation & Biology 14(1), 56–63 (2015).
- J. Harding, Amphibians and Reptiles of the Great Lakes Region (The University of Michigan Press, Ann Arbor, Michigan, 1997).
- D.M. Delaney, F.J. Janzen, D.A. Warner, Nesting stage and distance to refuge influence terrestrial nesting behavior of Painted Turtles (Chrysemys picta). Canadian Journal of Zoology 95, 837-841 (2017).
- C. Celley, USFWS. Painted turtle laying eggs. Flickr. 22 June 2019. https://www.flickr.com/photos/usfwsmidwest/48119801783/in/photolist-2gjbyAT-2bWJncZ-HGLAwL-cpS7FQ-3W9Q8M-S6xxm-S8uU8-RY8svb-S8vbK-2hmr2eJ-drX1Eh-TziuXk-S8uAr-25CA8Qo-HsATEE-M2UKxo-nNc11c-25CA9Yq-H568u4-p7bJ1z-H56914-Sjt9H-FW7CJk-qHE7Cy-gkWCEK-VS9V2M-gkW7ki-9uRFKR-YV9EZm-ECZegP-9uRESn-SgZjm-9uRFwt-9uUFA5-9uRExD-25CAaMj-9uRFZV-SgZFY-Tdkv4s-6HX8Nf-2gjbSFu-2gjbyYM-no4mXG-778fWq-SjsP8-gkWnzC-2GfyPy-ZeCprE-ufRQqY-2Gfyyj
- G. R. Ultsch, G. M. Ward, C. M. LeBerte, B. R. Kuhajda, & E. R. Stewart, Intergradation and origins of subspecies of the turtle Chrysemys picta: morphological comparisons. Canadian Journal of Zoology 79(3), 485 (2001).
- K.A. Marchand, R.G. Poulin, C.M. Somers, Western painted turtles (Chrysemys picta bellii) in a highly urbanized system: unexpected variation in resource use among age classes and sexes. Herpetologica 74(3), 217–225 (2018).
- D.J. Padgett, M. Joyal, S. Quirk, M. Laubi, T.D. Surasinghe, Evidence of aquatic plant seed -dispersal by eastern painted turtles (Chrysemys picta picta) in Massachusetts, USA. Aquatic Botany 149, 40-45 (2018).
- J.D. Congdon, R.D. Nagle, O.M. Kinney, R.C. Loben Sels, T. Quinter, DW. Tinkle, Testing hypotheses of aging in long-lived painted turtles (Chrysemys picta). Experimental Gerontology 38, 765-772. (2003).
- F. J. Janzen, Climate change and temperature-dependent sex determination in reptiles. Proceedings of the National Academy of Sciences 91(16), 7487-7490 (1994).
- L.E. Schwanz, and F.J. Janzen, Climate change and temperature-dependent sex determination: can individual plasticity in nesting phenology prevent extreme sex ratios? Physiological and Biochemical Zoology: Ecological and Evolutionary Approaches 81(6), 826-834 (2008).
- D. E. Pearse, J. C. Avise, Turtle Mating Systems: Behavior, Sperm Storage, and Genetic Paternity. J Hered. 92, 206–211 (2001).
- S.W. Veasey. Current climate predictions. U.S. Global Change Research Program, Global Climate Change Impacts in the United States 2009 Report. https://nca2009.globalchange.gov/report-credits/index.html
- R. S. Telemeco, D. A. Warner, M. K. Reida, and F. J. Janzen, Extreme developmental temperatures result in morphological abnormalities in painted turtles (Chrysemys picta): a climate change perspective. Integrative Zoology 8, 197-208 (2013).