Hebridensis

Nature in the Outer Hebrides

Home
Western Isles
Living Landscapes+
- Coast+
  - Coastal Animals
Fauna
Flora
Fungi
About
Wildlife Website Hub

Hebridensis > Western Isles > Living Landscapes > Coast > Coastal Animals > Jellyfish

Cnidaria: Jellyfish

There are five common species of jellyfish found around our shores – moon, compass, blue, barrel, and lion’s mane. They swim and drift on the currents feeding on plankton. Jellyfish move by pulsating contractions of the bell, and as they are not strong swimmers are vulnerable to being driven onshore by strong winds. They vary in size from between 30-90cm in diameter and the number and structure of the tentacles also differs between species.

Identifying Jellyfish on the Beach

Most of us encounter jellyfish when they are washed-up on the beach, so we have chosen photographs to illustrate the features you will see when they are reduced to "blobs" of jelly.
If you need help with identifying a jellyfish you find on a beach in the Outer Hebrides, you can post a photograph on the Outer Hebrides Biological Recording Facebook page.

Drifting in the clear shallow coastal waters of the Outer Hebrides, with the transulecent bell expanded and supported by the water, with the tentacles floating free, these elegeant animals are very different from the blobs of jelly found washed-up on the beach. It is possible to identify these amorphous blobs of jelly on the beach but take care as you can still be stung by the tentacles. You may also find some smaller marine invertebrates resembling jellyfish, washed up on the beach. These are usually comb jellies or by-the-wind sailors.

Compass Jellyfish Chrysaora hysoscella

Barrel Jellyfish Rhizostoma octopus

Also known as the dustbin lid jellyfish, this is one of the largest jellyfish found in our coastal waters. The dome is smooth, up to 90cm in diameter and varies in colour from white to pale pink, blue, green or brown.The rim is finely divided into lobes. On the undersurface there are four pairs of large arms, which are dived into lobes, each with thousands of mouth openings. This creates a frilled appearance.
Large numbers of barrel jellyfish have been recorded in the Irish Sea during the summer months. Leather-backed turtles, migrate to the area to specifically to feed on these jellyfish blooms.

Blue Jellyfish Cyanea lamarkii

Up to 30cm in diameter with a distinctive blue colour, although younger specimens may be paler. The margin of the bell has eight groups of 40-60 tentacles. On the undersurface there are four thick frilly oral arms, which are slightly shorter than the diameter of the bell.

Compass Jellyfish Chrysaora hysoscella

The diameter of the bell has 32 brown spotted semi-circular lobes, with 24 tentacles arranged in 8 groups. The slightly flattened bell is up to 30cm in diameter and has 16 V-shaped markings radiating from the centre. Hence the name of compass jellyfish. From the undersurface there are four central arms which are longer than the diameter of the bell.

Lion’s Mane Jellyfish Cyanea capillata

This is a large and spectacular jellyfish with a saucer-shaped dome from 30-50cm in diameter. Varying in colour from reddish brown to yellow, the rim has 16 lobes with 8 groups of tentacles, each comprising 70-150 tentacles. Beneath the bell there are four thick, folded arms which are shorther than the tentacles.

Moon Jellyfish Aurelia aurita

A translucent jellyfish apart from the 4 violet horseshoe shaped gonads. The saucer-shaped bell is usually less than 25cm in diameter. There are 8 notches in the rim which has short tentacles. There are 4 thick centrally positioned arms under the bell.