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Jellyfish

Barrel Jellyfish

Rhizostoma octopus

Rhizostoma octopus (Gmelin, 1791) · Rhizostomatidae WoRMS 152203

Reference photos

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One of the largest jellyfish in UK seas, with a solid, rubbery bell up to 90 cm across, smooth and slightly flattened, and no marginal tentacles. Eight thick frilled arms hang beneath it, and the sting is generally weak.

Depth

Pelagic in shallow coastal water, from the surface down to about 20 m, moving up and down through the whole water column dozens of times a day.

Size

Bell up to 90 cm across, and reported to reach 1 m; weighs as much as 35 kg.

Habitat

Pelagic in coastal seas, aggregating in bays and also found in open water.

Behaviour

Gathers in large aggregations in coastal bays, and swims actively up and down the whole water column rather than drifting passively.

Diet

I eat

  • Plankton, filtered from the water rather than actively hunted
  • Phytoplankton, copepods and other small zooplankton, with crustacean and mollusc larvae
  • Small prey trapped in the frilled oral arms and swept to the mouth by microscopic hairs

Eats me

  • Leatherback turtles, for which it is a major prey item
  • Ocean sunfish, another fast-moving predator of it

Where you'd find it

Mostly seen in the English Channel, the Celtic Sea and the Irish Sea, and only here and there elsewhere.

ChannelCeltic SeaNorth SeaIrish SeaW of IrelandW of Scotland
Often seenNow and thenWhere PEBL filmsBased on marine survey records (OBIS). Blank seas can mean nobody has looked there, not that the animal is absent.

Sources

Open-access references behind this page. Every statement on this page was read out of one of them; anything that could not be traced to a source was taken off the page rather than left standing. Each link was checked on the date shown, and confirmed then to be about this species.

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