Re: Hallaxa michaeli on food sponge

September 14, 2009
From: Leanne and David Atkinson

Dear Bill,

To answer your questions about ascidians in our previous message [#22626]. We found the Hallaxa michaeli on sponge on an ascidian. This ascidian is often at the base of the stalked ascidians. There weren't any stalked ascidians in the immediate vicinity but there are plenty in the general area. We dive here at high tide to take advantage of the slack water. There is a very strong current that moves through the area with changing tides and we have witnessed nudibranchs launch themselves or lose their grip and be swept away by the current on occasions. It would be possible for them to have travelled to this ascidian from a stalked one. We have included photos of ascidians from the general area. The middle photos are of the type of ascidian we found them on. They were on the upper surface of the longer arm of the v shape you can see in profile. It was hard to get a photo without having part of the other arm of the v in it so they would be quite well protected in this spot. The lower photo is a single stalked ascidian with one of these at the base. The upper photo is of a group of the stalked ascidians with another one of these at the base we think, it is a bit overgrown and we are not confident of our knowledge about these particular ascidians.

Locality: Halifax Sponge Gardens, Port Stephens-Great Lakes Marine Park, Port Stephens, 10 to 12 metres, Pacific Ocean, 06 September 2009, Sandy bottom with some rocky reef with scattered sponges, ascidians, bryozoans and gorgonians. Length: 160 mm to 300 mm. Photographer: Leanne and David Atkinson.

Hope this answers your questions thank you for your help with our questions.

Best wishes,
Leanne & David Atkinson

atk@hunterlink.net.au

Atkinson, L. & D., 2009 (Sep 14) Re: Hallaxa michaeli on food sponge. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22658

Dear Leanne and David,

Thanks for the information. It certainly looks as though the Hallaxa is not interested in the ascidians for their sake, but because they are the preferred 'home' of the sponge it feeds on. Like you, I am not an expert on ascidians so I can't really say if the unstalked ascidians are a growth stage or form of the stalked ones, but I am sure that observations like this will be useful in the future for anyone studying, not just the local nudibranchs, but also the  sponges and the ascidians.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Sep 14). Comment on Re: Hallaxa michaeli on food sponge by Leanne and David Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22658

Factsheet

Hallaxa michaeli

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