Researchers have documented three cases of cannibalism in wild members of the common octopus species – Octopus vulgaris. Previous studies of stomach contents have suggested the existence of cannibalism in wild O. vulgaris in the Western Mediterranean Sea and the South Atlantic. The new research confirms that cannibalism also occurs in octopuses inhabiting the Northeastern Atlantic, which suggests that such behavior "is widespread throughout the distribution range of O. vulgaris," the researchers wrote in the study. [Read full story]
Partially Eaten, Dead Prey
This is a photo of the first of the three recorded cannibalism cases. It shows a male octopus leaving a dead and partially eaten small octopus (upper right) after being disturbed by the diver who was documenting the case. [Read full story]
In this image of the second recorded case of cannibalistic behavior, a male O. vulgaris is shown wrapping an octopus inside the sack formed by the arms and the web (the skin between its arms). The diver who recorded the case realized that "the prey was still alive, because it poked and moved one of its arms between the dorsal pair of arms of the predator," the researchers wrote. The diver disturbed the predator, which in turn let go of the prey, letting it escape, and therefore the researchers classified this case as "an attempted predation." [Read full story]
In the third recorded case, a female of O. vulgaris is shown hidden in a cavity, holding a dead and partially eaten smaller octopus. [Read full story]
Choosing to Cannibalize
Even if an octopus has access to more "traditional" prey such as mussels, it may still choose to feed on another, smaller member of its own species. [Read full story]
When octopuses are in captivity, and too many of them are introduced to the same aquarium or an on-growing cage (a floating cage where octopuses are reared), they may resort to cannibalism as a means of defending their territory, said Jorge Hernández-Urcera of the Institute of Marine Research (IIM) in Vigo, Spain. Territoriality is also one of the possible causes of cannibalism in O. vulgaris in the wild.
"The existence of territoriality in octopuses is, however, controversial," he said, adding that some reports confirm territorial behavior in octopuses, whereas others reject it. [Read full story]
The researchers think the most probable cause of cannibalism in the cases observed in the study is the high net energy gain, which translates into the balance between the energy that octopuses use to catch and eat the prey and the energy they get from feeding on it, Hernández-Urcera said. When an octopus chooses to feed on another member of its species instead of mussels, it may do so because it can get more protein per gram from octopus meat compared with mussels. [Read full story]
Moreover, handling another octopus as prey requires less energy than opening the number of mussels whose weight would be equivalent to the weight of meat provided by a single octopus, Hernández-Urcera said. [Read full story]
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