Bluebottles and by-the-wind sailors, sea surface predators. Abel Tasman National Park

Bluebottles and by-the-wind sailors, sea surface predators. Abel Tasman National Park

Every so often after a big onshore blow,  we get large wash ups of these beautiful creatures.  The Indo-Pacific Portugese Man o’ War or Bluebottle (Physalia utriculus) and  the by-the-wind-sailor (Vellella vellella) are the only ocean going species that occupy the  ‘pleuston’ niche (half in and half out of the water). They both start their lives in the mid-ocean ‘blue water’ and find themselves washed up on distant shores.

Portugese man o' war
Bluebottle Jelly Fish / Portugese man o’ war (Physalia utriculus), Abel Tasman National Park, Photo: Stew Robertson

Bluebottles are not classic cnidarian jelly fish,  but colonies of hydroids, known as siphonophores,  They are composed of four separate colonies of polyps and medusoids. The colony comprises a gas-filled polyp called a pneumatophore that keeps it afloat, and three other polyp types called the gastrozooids (digestive cells), gonozooids (reproductive cells) and dactylozooids (stinging tentacles).  The dactylozooids fire nematocysts (stinging cells) at zooplankton and small fish swimming below, bringing them up to the gastrozooids for consumption and distribution to the rest of the colony.  The Pacific bluebottles are distinct from the Atlantic species Physalia physalis in that they only have one long tentacle and are generally smaller.

Abel Tasman National Park
By-the-wind-sailor (Vellella vellella), washed up in the Abel Tasman National Park, New Zealand. Photo: Stew Robertson

By-the-wind-sailors (Vellella vellella) are the only species known in the Porpitidae family of Hydrozoa.  They have a similar colonial form to the Bluebottle,  however instead of a pneumatophore,  they have a rigid sail that carries them on the wind,  giving them their common name.

Both species are known to be predated on by by Purple Janthina snails and pelagic nudibranchs which also float near but not out of the waters surface.  Loggerhead turtles and ocean sunfish are also thought to feed on them.

In large numbers, these can have huge impacts on fish recruitment.  In Australia 10,000 – 30,000 bluebottle stings are reported every year, often leading to the closing of beaches.  We regularly see these in the shores of the Abel Tasman,  however,  if caution is exercised,  we don’t see many dramas.  Unlike other jellyfish,  vinegar or urine (we keep both on the boat!) is not the wisest treatment as it can aggravate the injury further.  Heat packs,  are the way to go and then the area should be treated with shaving cream and shaved with a clean razor to remove the stinging cells (might have to update the first aid kit!).  Hydrocortizone cream is also recommended.

Although we saw a lot today,  don’t worry they are a mid ocean wanderers and will be gone tomorrow once the wind swings round!

By Stew Robertson

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