you're reading...


Why Do Sea Turtles Get Tumors?

Paper: Keller, J. M.; Balazs, G. H.; Nilsen, F.; Rice, M.; Work, T. M.; Jensen, B. A. Investigating the Potential Role of Persistent Organic Pollutants in Hawaiian Green Sea Turtles Fibropapillomatosis. Environ. Sci. Technol. 2014. DOI: 10.1021/es5014054


Green sea turtles (Chelonia mydas) worldwide are afflicted by tumors that can impede their movement, block their sight, and prevent them from feeding. The tumors are caused by a disease called fibropapillomatosis, which is now known to be viral and contagious, especially among juvenile sea turtles. Alarmingly, in some areas 50-70% of turtles have contracted the disease, threatening the existence of turtle populations.

Stranded sea turtle with severe fibropapillomatosis

Stranded sea turtle with severe fibropapillomatosis (Source: news.wildlife.org)

Do Chemical Pollutants Cause Sea Turtle Tumors?

Previous studies show that turtles living closer to populated areas have higher rates of these tumors, suggesting that environmental stressors could make turtles more susceptible to fibropapillomatosis. In recent studies, scientists have been trying to identify which of the various stressors associated with human land use is the culprit: Could it be biotoxins arising from algal blooms caused by increased nutrients in the water, or chemical pollutants that don’t break down in the environment and accumulate in the turtles’ bodies?

In this study, Jennifer Keller and others set out to determine whether persistent organic pollutants, a broad class of chemicals released by human activities, may make sea turtles more vulnerable to contracting fibropapillomatosis. Persistent organic pollutants are chemicals like flame retardants, plasticizers, and insulators that leach out of consumer products or are emitted from manufacturing facilities, and don’t break down easily in the environment. They are hydrophobic and bioaccumulative, meaning that they are attracted to fatty tissues and accumulate readily in organisms.

Many persistent organic pollutants have been taken off the market because they are carcinogenic (cancer-causing) or immunosuppressant (weaken the immune system), but they still remain in the environment due to their persistence. Researchers have found that sea turtles, as well as many marine mammals and fish, accumulate persistent organic pollutants through their diets and through exposure to sediments. Turtles with fibropapillomatosis have weaker immune systems than healthy turtles, suggesting that some sort of stressor suppressing the immune system could increase their susceptibility to the disease.


 Locations of turtles in the study.

Figure 1: Locations of turtles in the study. Yellow triangles indicate stranded turtles and blue markers are sites where non-stranded turtles were captured. 13 non-stranded turtles were captured at each of the three blue sites. No turtles captured at Kiholo showed signs of tumors. 8% and 38% of turtles had tumors at Kailua Bay and Kapoho, respectively. (Source: Keller et al.)

The scientists took blood samples from 14 stranded, sick turtles and 39 free-ranging turtles that they caught along the shores of three different Hawaiian sites. The three locations where free-ranging turtles were captured had significantly different prevalence of tumors: At one site, no turtles with tumors were found, while at the other two sites, 8% and 38% of turtles had observable tumors. The stranded turtles were from a variety of locations, and they consistently showed the most severe cases of fibropapillomatosis, suggesting that the disease caused their stranding.


The sick, stranded turtles had the greatest concentrations of persistent organic pollutants in their blood plasma. Does this mean that pollutants made them more susceptible to the disease? The authors state that it is actually unlikely that the measured pollutants caused contraction of the virus, as they also found that the stranded turtles had the lowest lipid content, suggesting these turtles were having trouble finding food and hadn’t eaten recently, and so were using up their stored fat to survive. As the turtles used up their fat stores, pollutants accumulated in the lipids would have been mobilized and released into the blood. This means that increased concentrations of chemical pollutants in the blood of stranded turtles may be more a symptom and less a cause of fibropapillomatosis. However, the release of these pollutants during weight loss in later stages of the disease could make turtles sicker and contribute to their rapidly deteriorating condition.

What about the healthier turtles in the study? Pollutant concentrations were significantly different depending on where turtles were collected, but not in the way researchers had hypothesized. Concentrations were actually greatest in the sea turtles from the “low disease” site where 8% of turtles had tumors (though these turtles still had lower concentrations that stranded turtles). This site was the most densely populated by humans of the three study sites, which helps to explain greater pollutant concentrations but confounds the hypothesis that pollutants are making turtles more susceptible to fibropapillomatosis.

pollutant concentrations

Figure 2: A comparison of pollutant concentrations in the four groups of turtles. PCBs are banned chlorinated pollutants that were previously used in electrical equipment and other infrastructure. PBDEs are a recently banned class of brominated flame retardants. 4-OH PCB 187 was identified by the researchers as a metabolite of PCBs, produced by the turtles after exposure. 6-OH PBDE 99 and 6-OH PBDE 47 are most likely natural products from algae consumed by the turtles. Pentachlorophenol and 2,3,4,6-tetrabromophenol are pollutants about which less is known than PCBs and PBDEs. 2,4,6-tribromophenol is both a manmade pollutant and a natural product of some algal species. (Source: Keller et al.)


This study provided the most comprehensive survey of sea turtle fibropapillomatosis and persistent organic pollutant accumulation to date. While the persistent organic pollutants measured in this study don’t seem to be making turtles more vulnerable to tumors, they might worsen the disease at later stages as weight loss causes mobilization and immunosuppression.

While this study doesn’t explain why turtles in some areas develop tumors and others are healthy, the researchers did contribute valuable new information to our knowledge of pollutant accumulation in turtles. They observed that human population density and weight loss both lead to higher concentrations of pollutants in sea turtle blood and they identified some novel pollutants that had not been previously measured in sea turtles. Their observations about varying concentrations of pollutants at the different Hawaiian sites could help to determine sources of these contaminants.

Additionally, the team detected some compounds in the turtles that look like contaminants but may actually be natural products produced by algal species that the turtles eat. Concentrations of these compounds decreased in the blood plasma of turtles that exhibited weight loss, while persistent organic pollutants increased.



  1. […] Want more turtles: read past Oceanbites posts here, here, here, and here. […]

Post a Comment


  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 7 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 9 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 10 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 11 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 12 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com