Tuesday, March 6, 2012

The Turtle & the Octopus

Hapalochlaena sp. from New South Wales. Photo
Credit: David Brenemen
Moreton Bay in Queensland, Australia is estimated to support 20,000 sea turtles. The bay has extensive seagrass beds used as feeding areas by the green sea turtle, (Chelonia mydas). The seagrass beds also provide habitat for many marine creatures, including the blue-lined octopus, Hapalochlaena fasciata, a visually cryptic species that hides in tide pools by blending with its surroundings using pigmented chromatophores. When threatened, the octopus displays bright blue rings and lines, which act as a warning to potential predators. The blue-lined octopus delivers the neurotoxic tetrodotoxin (TTX) when it bites, a molelcule that has been hypothesized to be used for defense although evidence to support this has been absent. Two dead adult green sea turtles were recently found in Moreton Bay, despite the outward appearance of being healthy, the turtles showed no life threatening injuries. Upon dissection both turtles appeared normal, their digestive tracts contained large quantities of the seagrass (Halophila ovalis) and inspection of the contents revealed a bluelined octopus encased within a seagrass bolus in each of the two turtles. In both cases esophageal tissue directly around the octopus was red and inflamed suggesting the turtles had been envenomation, further tests on the turtles' tissues confirmed TTX poisoning. This case provides the first evidence of the octopus using TTX as a possible defense mechanism, and is the first evidence to suggest that this small octopus is a hazard to turtles.

CitationKathy A. Townsend, Jens Altvater, Michael C. Thomas, Qamar A. Schuyler and Geoffrey W. Nette. 2012. Death in the octopus’ garden: fatal blue-lined octopus envenomations of adult green sea turtles. Marine Biology 159, 689-695

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