Friday 23 December 2016

Brooding behaviour in deep sea Incirrate Octopus.

Incirrate Octopus (Octopus without membranes connecting their legs) are important parts of most benthic marine communities, and in deep sea environments are among the largest predators. Female Octopus brood their eggs, remaining with and protecting them until the young Octopus hatch, which usually coincides with the death of the parent. This behaviour has been observed in Octopus at depths of down to about 3000 m, with one specimen off the coast of California being observed to brood a clutch at a depth of 1397 m for over 53 weeks, the longest observed brooding behaviour in any animal, a period which was probably necessary due to the extremely low temperature at this depth, which would slow the metabolism of the developing eggs.

In a paper published in the journal Current Biology on 19 December 2016, Autun Purser of the Alfred Wegener Institute, Yann Marcon, also of the Alfred Weganer Institute, and of the Center for Marine Environmental Sciences, Henk-Jan Hoving of the Helmholtz Centre for Ocean Research, Michael Vecchione of the NOAA National Systematics Lab. at the National Museum of Natural History, Uwe Piatkowski, also of the Helmholtz Centre for Ocean Research, Deborah Eason of the Department of Geology and Geophysics at the University of Hawai‘i at Manoa, Hartmut Bluhm, also of the Alfred Weganer Institute, and Antje Boetius, agian of the Alfred Weganer Institute, and of the Center for Marine Environmental Sciences, and of the Max Planck Institute for Marine Microbiology, describe nesting behaviour in deeps sea Incirrate Octopus from depths of between 4120 and 4197 m on the deep Ka‘ena and Necker Ridges of the Hawaiian Archipelago, and in a nodule-abundant region of the Peru Basin.

The Octopus were observed between 2011 and 2016 using remote operated vehicles and towed cameras. Twenty nine individual Octopus were observed, and while it was not possible to identify them to species level, there were at least two species observed, one being translucent and having a single row of suckers on each arm (refered to as the 'Casper' morphotype), while the second was more opaque and had two rows of suckers on each arm, possibly being a species of Vulcanoctopus.

The morphotypes of deep-sea incirrate octopods observed in the study. (A) The Necker Ridge ‘Casper’ Octopod (4,290 m), 6.4 cm mantle length, slowly crawling across a basalt outcrop.  (B) Octopod observed in the deep Peru Basin nodule rich DISCOL experimental area (4,099 m), mantle length ~9 cm, potentially Vulcanoctopus sp. (C) The Ka‘ena Ridge ‘Casper’ Octopod (3,116 m), mantle length 6.5 cm, utilising a nook in a pillow basalt. (D) A ‘Casper’ Octopod observed in the DISCOL area (4,151 m), mantle length 5 cm, the most abundant morphotype observed in the region. Purser et al. (2016).

Two Octopus were observed brooding clutches of eggs on the stalks of dead Sponges in fields of manganese nodules, at depths of 4150 and 4181 m, in the Peru Basin. Given the extremely low temperatures at depths bellow 4000 m, typically about 1.5 °C, Purser et al. suggest that these Octopus are likely to have extremely long brooding periods, possibly years in length. The Sponges upon whose stalks they grow are known to be extremely dependent on the presence of the manganese nodules and highly sensitive to disturbance of the environment, potentially placing them at risk from proposed schemes to mine manganese from the sea floor. Purser et al. suspect that these Octopus, which seem dependent on the presence of both the manganese nodules and the Sponges, would be even more sensitive to environmental disturbance of the nodule fields.

Brooding eggs at the approximate mid-point of a dead Sponge stalk, itself attached to an underlying manganese nodule. Purser et al. (2016).

As well as the Octopus brooding eggs on Sponge stalks other individuals were observed in cracks, joints and fissures in manganese nodules and exposed basalt rocks on the seafloor. The Octopus appeared to have cleaned the sediment around these locations, possibly as a result of foraging behaviour; some specimens were observed with their limbs penetrating the sediment, in some cases undulating their limbs while doing this.

Typical Octopod behaviours observed during the current study. (A) Flat on seafloor, tentacles extended and curled, (B) curled close to manganese nodule, (C) flat on seafloor, penetrating sediment with undulating tentacles, (D) curled between two adjacent manganese nodules. Purser et al. (2016).

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