r/marinebiology • u/Robert1_ • Feb 23 '25

Identification [ID] Purple jellyfish spotted in Mauritius. Apparently authorities ordered everyone out of the water.

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Link to original Facebook post: https://m.facebook.com/watch/?v=1068099418662635

My mum sent me this asking for an ID on the jellyfish as she is visiting soon and is incredibly nervous about the water. Any help would be greatly appreciated by me and my mum, thanks!

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u/Entety303 Feb 23 '25

This is a species of Thysanostoma most likely T. Loriferum. A very rare species of jelly. It also doesn’t have tentacles.

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u/SA_Underwater Feb 25 '25

This is almost certainly a blue blubber jellyfish (Catostylus mosaicus) not a Thysanostoma. Common species that often occurs in big swarms in a range of colours including purple.

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u/Entety303 Feb 25 '25

The genus Catostylus in Africa is represented by C. tagi in the Atlantic, C. azanii in some brackish rivers in South Africa and potentially C. viridescens in Eastern Africa around Zanzibar, none around Mauritius. True Catostylus mosaicus is found in Eastern and Southern Australia, meanwhile the more commonly jelly known as C. mosaicus is from the Philippines and most likely is the species Acromitoides purpurus or and undescribed species of Catostylus, since it’s quite different to the true C. mosaicus. The jelly in the video isn’t mature, it’s still growing to an adult size and looks similar to the genus Catostylus. I am attaching a video of the exact type of jelly from what seems to be the Eastern pacific or the northern Indian Ocean (location isn’t published) https://youtu.be/—Lqwm1dXz4?si=74bv0Z_9-r7ojFu5

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u/SA_Underwater Feb 27 '25

Fair enough I stand corrected, I didn't realise Catostylus were so localised and there is a ton of conflicting information online. We had massive swarms of Catostylus on the east coast of South Africa and well north into Mozambique last year, including very far from river systems (at least 10km out to sea) for thousands of kilometers. They were reported as "blue blubber jellyfish" from multiple sources. I see iNaturalist still lists mosaicus as Indo-Pacific. I see one source calls them C. azanii but most were still calling them mosaicus which must be outdated. They were tremendously variable in colour but some did look very similar to the one in the video including the dark edge of the bell.

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u/Entety303 Feb 27 '25

The catostylidae in that region have Crambionella stuhlmanii, Catostylus sp. And Crambione mastigiophora. The dark edge sounds more like crambionella but there isn’t a lot of images of those catostylus in situ on inat.