Re: Food of Dutch Geitodoris planata

August 30, 2001
From: Bernard Picton

Hi Bill,
I see you recently posted Peter van Bragt's pictures of Geitodoris planata. He emailed me to say that Rob van Soest had identified the food as Mycale micracanthoxea (see separate message). Rob is a top world sponge expert)

Now it is very interesting that this sponge appears to occur primarily in the Oosterschelde and to be very common there. It was first found in the neighbouring Westerschelde in 1953 and van Soest also had a Vosmaer specimen from Bergen op Zoom which was undated. van Soest says in his 1976 paper that the sponge is exclusively known from Dutch waters.

I wonder if we are seeing here an introduced species of sponge - therefore vulnerable to the (Mycale eating) Geitodoris, which has now found the sponge and will have a big impact on its populations?

Bernard

bernard.picton.um@nics.gov.uk

Picton, B.E., 2001 (Aug 30) Re: Food of Dutch Geitodoris planata. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5171

Thanks Bernard,
It's very interesting idea. Introduced 'foods' can certainly introduce strange events in local ecosystems. I have mentioned an example in New Zealand, elsewhere in the Forum concerning Rostanga muscula. A feeding study by Ayling (1968) showed that in Auckland three poecilosclerid sponges were eaten by this species and there was a clear order of preference. Interestingly, its second favourite food was later discovered to be Clathria seriata, an introduced species from Europe which disappeared after a brief period of 3 years.

If, as you suggest, Mycale micracanthoxea does turn out to be an introduced species which Geitodoris planata has found particularly tasty, it would explain the unusual population explosion of this species in the Netherlands.
Best wishes,
Bill Rudman.

Rudman, W.B., 2001 (Aug 30). Comment on Re: Food of Dutch Geitodoris planata by Bernard Picton . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5171

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