Sunday 31 August 2014

Brooding behaviour in a Deep-sea Octopus.

Most Octopus reproduce only once in their life cycle, with the female undertaking an extended period of brooding in which she tends her eggs, keeping them clean and oxygenated and protected from predators, expiring at the end of this period. In most species the female does not feed at all during this period. Species producing more developed offspring will tend to have longer brooding periods, as will species with brooding their offspring in cooler waters, where development occurs more slowly. Females of the Deep-sea Octopus Graneledone boreopacifica have previously been observed to brood a clutch of young for over 20 months, though the full reproductive cycle has never been observed, and it is therefore assumed to be somewhat longer. Even this partial observation gives the species the longest known brooding period of any Octopus, with the next longest being 14 months for the full cycle in the Arctic Octopus, Bathypolypus arcticus.

In a paper published in the journal PLoS One on 30 June 2014, Bruce Robison of the Research Division at the Monterey Bay Aquarium Research Institute, Brad Seibel of the Department of Biological Sciences at the University of Rhode Island and Jeffrey Drazen of the Department of Oceanography at the University of Hawaii, describe the full brooding period of the Deep-sea Octopus Graneledone boreopacifica for the first time.

Robison et al. first observed a female Deep-sea Octopus on an isolated rocky outcrop in the Monterey Submarine Canyon off the coast of central California at a depth of 1397 m using a remotely operated vehicle (ROV) in April 2007. At that time the female was a pale purple in colour and was moving over the rock surface. When the ROV returned to the same sight in May 2007 (38 days later) the same Octopus was seen to be nursing a clutch of eggs and had faded to almost white in colour. This provided a unique opportunity for the observation of a full brooding cycle in a female Deep-sea Octopus. 

Graneledone boreopacifica, female brooding her eggs on a nearly vertical rock face at a depth of 1397 m. The pale columns are stacks of eggs deposited and left behind by the Snail Neptunea amianta. Near the Octopus are two Lithodid Crabs and a nonbrooding Graneledone can be seen above and to the right of the brooder. The mantle length of the specimen, when first encountered, was 21.2 cm. Robison et al. (2014).

The Octopus had a distinct, enabling the confirmation that the same animal was being observed throughout the study. While it was not possible to observe continuously, the ROV did revisit the sight 18 times over the next four and a half years, on each occasion finding the Octopus brooding her eggs, until the final visit in October 2011, when the eggs were observed to have hatched and the mother was absent.

Graneledone boreopacifica, brooding female, May, 2007, on the rock face, covering the recently deposited clutch of eggs. The arrow points to a circular scar on arm L1, which provides additional confirmation. Robison et al. (2014).

This confirms that the Deep-sea Octopus Graneledone boreopacifica, has the longest known brooding period of any Octopus, at approximately 53 months. This also exceeds the brooding period of any known non-Octopus species; exceeding the 2 month continuous brooding period of the male Emperor Penguin, the 4-5 month period of the Magellan Plunder Fish, Harpagifer bispinis, (the longest known brooding period of any Vertebrate) and the 20 months of the Mysid Crustacean Gnathophausia ingens, which until now was the longest known brooding period of any animal. It also exceeds the longest gestation periods known in live bearing species, outlasting the 20-21 months seen in Elephants, the 42 months of the Frilled Shark and the 48 months seen in Alpine Salamanders.

Empty egg cases, October 2011. This is a composite figure, showing empty egg cases, and attachment sites (indicated by green cement residue), used to enumerate the number of egg cases in the clutch, after hatching. Robison et al. (2014).

See also…

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