Observation of a Gelatinous Octopod, Haliphron atlanticus, along the Southern West Mariana Ridge: A Unique Cephalopod of Continental Slope and Mesopelagic Communities

Abstract

The circumglobal deep-sea gelatinous giant octopod, Haliphron atlanticus, reaches 4 m in length and uses both benthic and pelagic habitats in the upper 3000 m of the ocean during different life history stages, but it is rarely observed due to the deep-depths where it typically lives. It has been collected in trawls and observed a few times near continental margins or islands and has been identified in the stomach contents of deep-diving predators such as sperm whales and blue sharks or detected as body fragments after predation events. An individual H. atlanticus (∼1 m in total length) was video-recorded at 12:21 for about 3 minutes in front of the Shinkai 6500 submersible at 586-599 m (6.5 ∘ C, salinity 34.4) along the West Mariana Ridge. It made no escape attempt as the submersible approached and it moved slowly up or down in front of the submersible. It was over the outer seamount-slope (bottom depth ∼3208 m) ∼50 km west of seamounts (≥1529 m summits), but how it fits into the mesopelagic food web along the ridge is unclear. More information is needed to understand the role of H. atlanticus in oceanic food webs and if it typically lives along seamount ridges.

Capture of the Coronate medusa <i>Periphyllopsis braueri</i>, by the Giant Seven-arm Octopus <i>Haliphron atlanticus</i>

“…The notion that deep-sea cephalopods that eat medusae might use the stinging abilities of their cnidarian prey to obtain more nutrition is an intriguing, although unproven, idea. Miller et al (2018) noted an apparent escape response during two separate observations of Haliphron by other authors, but no escape response for the individual of Hoving and Haddock (2017) that was holding a jellyfish in its arms in a manner similar to that described here. Rosa et al (2017) discuss the hitchhiking behavior of one Haliphron holding onto the oral side of a jellyfish.…”

“…Recently, there have been reports of a few live observations of Haliphron (e.g. Miller et al 2018) including some associated with jellyfish (Hoving andHaddock 2017, Rosa et al 2017). Possible explanations for such associations include as an energy-saving mechanism (riding on the medusa), defense (using the tentacles against potential threats), and predation events.…”