Water wildlife: Sea gooseberry

Susanne Masters introduces us to the sea gooseberry (Pleurobrachia pileus), an iridescent comb jelly that refracts light like a rainbow.

If rainbows were alive this is one of the creatures they would be. See-through sea gooseberries catching a beam of sunlight in water become outlined in a rainbow shimmer. The colourful part of this effect is light refracting on cilia arranged in rows, like a comb, on their body. Shimmering is caused by the cilia, as the sea-gooseberry beats them in waves to move through water. Their two tentacles are also rendered more visible by light at the right angle to highlight filaments on them. These tentacles are used for catching small prey like copepods, tiny crustaceans, and won’t sting human skin.

On dry land when sea gooseberries are washed ashore, they look and feel like squelchy marbles, about 2cm in diameter. Many records of their presence come from stranded sightings. You are most likely to encounter them near the surface of the sea in warm months in the afternoon, as in the early morning they descend to deeper water and in winter they stay near the seabed. Seeing them in the sea relies on clear water, and swimming speed that is leisurely enough to catch a glimpse and quickly pause to enjoy the view.

Where to see a sea gooseberry

• Long Sands Beach, Tyne and Wear
• Blue Pool, Abereiddy, Pembrokeshire • Gorleston Beach, Norfolk
• Wicklow Harbour, Co. Wicklow

This article is from the May 2023 issue of Outdoor Swimmer. Click here to subscribe to the magazine. Illustration: Alice Goodridge.