What the ?

March 23, 2006
From: Eve Whicker

Hi -
I am very curious about Blue Sea Slug [Glaucus atlanticus] behaviour - - - last weekend we had a huge wash up of Blue Bottle and Slugs on my home beach at New Brighton, just north of Byron Bay. We brought several specimens home to take some photos. Over the course of the afternoon I put them in a container together to get some pix of them en masse and the two largest joined up, rolled over, stayed that way for about 5 minutes then separated with a thingy (?) coming out of their sides. One turned over immediately, the other took a minute or two. I can't imagine that they have a need for male combat but then again who knows ? does any one have a clue ?

Locality: New Brighton Beach, nthn New South Wales, Australia, 18 March 2006. Length: largest 4 cm. Photographer: Eve Whicker.

Eve Whicker

eveii@bigpond.com

Whicker, E., 2006 (Mar 23) What the ? . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16154

Dear Eve,
I don't think this is related to sex, I suspect its related to close proximity in a bottle. Although Glaucus usually feeds on Bluebottles it is related to other glaucid aeolids which are quite feisty and are known to attack and eat their own kind. Have a look at the photos of Phidiana hiltoni {message #2716] fighting. Another name for this species, Phidiana pugnax, was given to it because of its pugnacious behaviour. So what I think your two animals are doing is biting each other. I don't know if this is normal behaviour because we don't know much about their normal behaviour. So far no student has been silly enough to float around with Blue bottles and Glaucus to record their behaviour.

Have a look at an earlier message [8233] for a photo of the penis. If that is what you saw, then it is also related to close proximity. Animals which float around in the sea most of the time are probably adapted to mating quite quickly when they 'make contact' with another of their kind. Your lower photo shows the brilliant silvery colour on the back of Glaucus. However as these animals spend their time floating upside down the silvery colour will be on the functional underside of the animal. If you compare this with pelagic fish, such as tuna, you will see a remarkably similar colour pattern - silver below, dark blue above. This is called 'countershading' and helps to render the animals invisble from predators below in the water and above in the sky.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Mar 23). Comment on What the ? by Eve Whicker. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16154

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