Species Report Rhopilema Nomadica (Nomad Jellyfish)

Mediterranean invasive species factsheet www.iucn-medmis.org

Species report Rhopilema nomadica (Nomad jellyfish)

AFFILIATION CNIDARIANS

SCIENTIFIC NAME AND COMMON NAME REPORTS Rhopilema nomadica 18

Key Identifying Features

This solid, large jellyfish is light blue in colour with tiny granules on the bell. The bell of this jellyfish can range from 10 to 90 cm in diameter, usually 40–60 cm, and the whole animal can weigh 40 kg. Hanging from the centre are eight large mouth-arms divided at mid-length into two ramifications with numerous long filaments.

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Identification and Habitat

This species can form dense aggregations in coastal areas during summer months, although it can also appear all year round.

Reproduction

Its life cycle involves a small (usually < 2 mm) benthic polyp stage that reproduces asexually, and a large swimming medusa stage that reproduces sexually. Spawning usually occurs in July and August.

Similar Species

The most similar jellyfish is the native Mediterranean Rhizostoma pulmo. It differs from Rhopilema nomadica in its smooth bell surface and a dark purple band around its undulated margin. It has four pairs of very large mouth arms on its under surface but no tentacles.

Another common native species is Pelagia noctiluca. It is much smaller and mushroom-shaped, with a bell up to 10 cm in diameter. The medusa varies from pale red to mauve-brown or purple in colour and the bell surface is covered in pink granules. It has eight tentacles, pink in colour. The mouth arms can be 5 times the bell height.

Other species that look similar

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Economic Impacts

This jellyfish can inflict painful injuries to bathers and affect coastal tourism. Furthermore, large swarms can clog fishing nets, consequently reducing catches, and block cooling water intakes of coastal industrial facilities and desalination plants.

Management Options

Eradication may be impossible in practice. Public awareness campaigns to alert authorities, first-aid workers and the general public might prevent injuries caused by this species.