Endangered Green Turtle


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Picture credit: Stone Fish Movie

The green turtle, Chelonia mydas (Linnaeus, 1758), is highly exposed and affected by human activities and pollution, resulting in  CITES and  IUCN status « endangered ». According to scientists, plastic particles could have impacts on tissue and cellular levels within marine organisms. Thus, to develop effective measures to protect turtles against threats they face we need to know what exactly affect them, in which ways and with which intensity.

The green sea turtle, is one of the 7 marine turtle species. Its range extends throughout tropical and subtropical seas around the world and it can live 80 years in the wild. Posthatchlings oceanic stage is epipelagic and omnivorous with strong tendency to carnivory. After several years (20-25 cm curved carapace lenght) a non obligatory shift to coastal habitat occurs, becoming herbivorous in neritic zones primarily feeding on algae or seagrass. The green turtle is easy to identify using these external caracteristics:

Image from: Jeanette Wyteken (2001)

Because turtles grow slowly, are late to mature, and produce many eggs which few will mature, they are especially vulnerable to overfishing and slow to recover from depletion. Threats they face can be classified in 3 categories:

  1. Impact of tourism on nesting beaches
  2. Incidental catch through fisheries interaction and intentional fishing
  3. Impact of pollution (including ghost lines and nets)

A massive stranding of green turtles occured in 2012 in Upstart Bay, near Ayr in Queensland, with no obvious reason. This worrying event conducts to a 4 year-study at James Cook University to try to understand what led these turtles to death. Elsewhere, as plastic pollution is an emerging global issue, it cannot be excluded that plastic contamination could cause or contribute to disease or even to death of marine organisms, including turtles.
My project, which is part of the four-year study and of the « Marine Plastic Research » JCU hub, will investigate the digestive tract plastic contamination of 12 stranded turtles. These turtles have been collected by the association Eco Barge in 2014 near Airlie Beach in Queensland, unsuccessfully rescued, and conserved for future necropsy. Another team from the Veterinary school is studying virus on these same turtles. Among these turtles, 10 starved to death without any obvious reason neither, one has the intestine torn apart by a hook, one has the carapace open following a collision with a propeller, and 5 hatchlings died drowned in a stingers net. They were all immature, and died before having the chance to reproduce which is a shame for an endangered species with a slow life cycle.

Picture credit: Stone Fish Movie

In previous research, Stahelin et al. (2012) found a massive amount of debris in a stranded green turtle digestive tract, apparently blocking food passage and conducting it to death. « Starvation is the major cause of death for animals that ingest anthropogenic debris », affirm Laist (1987). Plastic debris can block food passage, or can cause partial obstruction of the digestive tract and reduce the feeding stimulus. Microplastics are also known to absorb persistent bioaccumulative and toxic compounds from seawater, which include persistent organic pollutants and metals, increasing their toxicity when ingested and becoming even more harmful to marine organisms. Moreover, von Moose et al. (2012), working on the blue mussel Mytilus edulis, provided proof of principle that microplastics are taken up into cells and cause significant effects on the tissue and cellular level. This would be possible in other (marine) organisms such as turtles, but it is an emerging area of research and it still needs to be investigated.

To analyse my 12 turtles, I will start with a spiking study, in order to test 2 different methods and to determine their sensitivity. Then, I will be able to start the « envrionmental exposure » study on my digestive tract samples. Let’s start with a lab induction this week, and experimentations soon!

References:
. Laist, D. 1987. Overview of the biological effects of lost and discarded plastic debris in the marine environment. Marine Pollution Bulletin 18:319-326.
. Morais, A. et al. 2014. Direct Evidence for Gradual Ontogenetic Dietary Shift in the Green Turtle,
Chelonia mydas. Chelonian Conservation and Biology, Volume 13, Number 2 – 2014.
. Stahelin, G. et al. 2012. Case Report: Ingestion of a Massive Amount of Debris by a Green Turtle (Chelonia mydas) in Southern Brazil. Marine Turtle Newsletter No. 135, 2012.
. von Moos, N., Burkhardt-Holm, P., & Köhler, A. 2012. Uptake and effects of microplastics on cells and tissue of the blue mussel Mytilus edulis L. after an experimental exposure. Environmental science & technology, 46(20), 11327-11335.
. Wyneken, J. 2001. The Anatomy of Sea Turtles. U.S. Department of Commerce NOAA Technical Memorandum NMFS-SEFSC-470, 1-172 pp.

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