Blue sea slugs are biological control of the stinging bluebottle

February 4, 2012 by · 1 Comment
Filed under: Beaches 
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Everyday Bluebottle Predators

I have always wondered what on earth eats the bluebottles that wash up onto our beaches during the summers. The bluebottles can give a very painful sting and can leave large welts on your skin. Bluebottles, or Pacific Man o’ War float on the surface of the ocean and move around with ocean currents and the wind. Bluebottles are ecologically known as plankton because they are organisms that drift on the surface of the ocean, without having any formal means of locomotion to move themselves. Bluebottles eat small planktonic organisms that come into contact with their stinging tentacles that hang into the water.

Bluebottle on sand at MacMasters Beach

Bluebottle washed up on MacMasters Beach  (Physalia utriculus)

The damage from the bluebottle sting

Skin welts caused by a bluebottle sting, courtesy Travelling.Steve, flickr

Killcare beach views - Marine Stingers sign

Bluebottle warning sign at Killcare Beach, courtesy Tim Gillin, flickr

Another type of floating organism that commonly washes up on our beaches is the  By-the-wind-sailor which has the special name of Velella velella. This animal is related to the bluebottles in that it also has stingers that capture small plantonic organisms, but this animal is not known to sting people.

By-the-wind Sailor on sand at MacMasters Beach

By the wind sailor washed up on MacMasters Beach

All animals have predators, and the By-the-wind sailors and Bluebottles that wash up on most east coast Australian Beaches are no exception. Recently at MacMasters Beach two really interesting animals washed up which are the natural predators of bluebottles, both are molluscs, one a snail, the other a sea slug or nudibranch. The common purple snail, has a “bubble raft” that enables the snail to float on the surface of the ocean and it is a predator of both the bluebottle and the By-the-wind sailor’s.

Common Purple Snail with bubble raft, courtesy wikipedia

The predator I find really interesting is the Blue Sea Slug, (Glaucus atlanticus), which is a predator not just of the bluebottle and the By-the-wing sailor, but also the Common Purple Snail. I collected a couple of these sea slugs, photographed and videoed them and then released them back into the water. Apparently these creatures travel upside down when floating, the stripy side is in fact the underside and the top is silver in colour. They eat the body of the bluebottles, and the stinging cells in the tentacles get stored in the slugs body and acts as a protection against predators.

Blue Sea Slug - Glaucus atlanticus

Blue Sea Slug from MacMasters Beach, it is about 20mm long

A little more information:

Common Purple Snail

By-the-wind Sailor

Bluebottles

Blue Sea Slug

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