Jellyfish
Jellyfish · Safety-caution species
Nemopilema nomurai · Aurelia coerulea
A planktonic invertebrate that paralyzes prey with the nematocysts (stinging cells) on its tentacles. The core of summer blooms is the large venomous Nomura's jellyfish and the native moon jellyfish — not a protected species, but a safety-management concern.
A drifting animal armed with stinging nematocysts
A planktonic invertebrate of the phylum Cnidaria (class Scyphozoa and others). Its tentacle nematocysts paralyze prey, and human contact can cause pain, rash, and systemic symptoms. The two key species are Nomura's jellyfish and the moon jellyfish.
Summer coastal blooms
In summer (mainly June–September), warm-current inflow and rising water temperature drive mass appearances along the coast. Native species have a year-round life cycle, while the presumed introduced species develops in the East China Sea and moves north into the South Sea, Jeju, and the East Sea.
Where to encounter jellyfish
Rather than a specific dive site, this is a caution species that appears region-wide along the South Sea, Jeju, and East Sea coasts in summer (June–September). In 2024 Nomura's jellyfish reached 108 individuals/ha, the highest density since 2015, and the moon jellyfish advisory came about a month earlier than usual.
A sting from the tentacle nematocysts can cause pain, rash, and systemic symptoms. It appears region-wide along the South Sea, Jeju, and East Sea coasts in summer, so minimize exposure.
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