A common jellyfish found off the Irish coast, the Barrel Jellyfish, Rhizostoma pulmo, has quite an extensive range. It is distributed in the Irish Sea, the Bay of Biscay, the North Sea, the Black Sea and is found extensively throughout the Mediterranean, so much so that it commercially fished (albeit on a small scale) off the coast of Turkey (1). It has even been found off the coast of Pakistan, where a record again associated with commercial fishing of the jellyfish was reported in 2007 (2). It is quite a striking animal, with a robust appearance and an ethereal, blushed mauve coloration. Despite their their relatively large size (up to 60 cm in diameter), and possibly due to an underreporting of cases, it was assumed for many years that this species was harmless to humans (3). However, this is no longer the case (4).
 |
| Barrel Jellyfish, Rhizostoma pulmo |
R. pulmo, like all jellyfish, is contradictory animal being as it is a relatively simple organism with quite a complex life cycle. This begins with the production of pelagic planulae by sexually mature adult that settle as polyps on hard substrates on the sea bed. These then metamorphose into strobilae, which reproduce asexually to form 8-rayed ephyrae. Up to eight of these may be produced per strobila. These detach to roam the pelagic zone where they mature into the adult medusae (5).
 |
| Barrel Jellyfish, Rhizostoma pulmo |
Adults produce Rhizolysin, a cytolysin, from their nematocysts for subduing prey. This has cytotoxic, hemolytic and clastogenic activity against human cells, which leads to irritation and the production of lesions upon contact with the skin (4, 6). Such lesions last for a few hours, but the subsequent pain can last for a period of days, causing considerable discomfort.
References:
- Omori & Nakano, 2001. Hydrobiologia 451 pp. 19–26.
- Muhammed & Sultana, 2007. JMBA2 Biodiversity Records (Published on-line) pp. 1–3.
- Addad et al, 2011. Marine Drugs 9 pp. 967-983.
- Kokelj & Plozzer, 2002. Contact Dermatitis 46 pp. 179-180.
- Fuentes et al, 2011. Marine Biology 158 pp. 2247-2266.
- Allavenaa et al, 1998. Toxicon 36 pp. 933–936.
