The jellyfish of Port Melbourne

The big blobby one — blue blubber

The blue blubber (Catostylus mosaicus) is the heavy, rounded jelly you'll see drifting on the tide, often in numbers. A firm, fleshy bell up to about 35 cm across, brown, bluish or white, with a pale cross showing through the top and eight frilly arms beneath. No long trailing tentacles. It's in the bay from spring through autumn.

The sting is mild — the stinging cells sit on the arms, not on long streamers, so a brush is a minor nip at most. What it has is bulk: sail over a solid one and you may feel it nudge the centreboard or rudder. No harm done, to you or it.

The stinger — lion's mane

The one to watch is the lion's mane (Cyanea annaskala) — native to Victorian and Tasmanian waters, pink to deep red, a ruffled bell trailing a mane of fine hair-like tentacles. The tentacles do the stinging, and they reach well beyond the bell.

It used to be a winter jelly here, rarely seen in the sailing season. That has changed. It bloomed thick along the sea wall between the Port Melbourne piers in January 2022, and again across the summer of 2024–25, part of bay-wide washes from Altona to the Peninsula. Warm water and onshore winds drive the blooms and push them inshore. They come anything from coin-sized to dinner-plate.

October 2026 — a few small lion’s mane were seen in the bay between St Kilda (RMYS) and Station Pier, about 500 m offshore, on the 18th. Small and early rather than a bloom, but worth knowing they were already in the sailing area before summer.

A bloom of lion's mane is the reason to keep hands out of the water and think twice about anyone swimming — the sting is sharper than the blubber's, and enough to close beaches.

Bluebottles — not a jellyfish at all

The bluebottle (Physalia) is a blue gas float with a single stinging tail — not one animal but a colony, and not a true jellyfish. It doesn't swim; the wind sails it. North-east winds blow them into the bay, mostly in summer. The sting is in the same class as the lion's mane, and the same first aid applies.

If you're stung

For the bluebottle and the lion's mane — the temperate stingers we get here — the steps are the same:

• Don't rub it, and don't handle the tentacles with bare hands.
• Lift off any tentacles — flick them with a gloved hand or the edge of something, or wash them away with seawater.
• Rinse with seawater, not fresh water. Fresh water sets off more stinging cells.
• No vinegar — it's for the tropical box jellyfish, and it makes these ones worse.
• Hot water is the painkiller: hold the stung part in hot water — about 45 °C, no hotter than you'd comfortably bathe in — for twenty minutes. A hot shower does it. A cold pack if there's no hot water.

A sting to the eye or face, a very large sting, or any sign of a whole-body reaction — trouble breathing, widespread swelling, faintness — is Triple Zero (000).

On the boat

Sailing through them is fine; the hull doesn't care. The risk is to bare skin in the water — a capsize into a bloom, or a hand trailed over the side. On a jellyfish day that's the whole of it: a wetsuit on, hands inboard, and swap the swim for another time.

When they're about

For why the water's cold enough to want a wetsuit in the first place, see the water-temperature page.