adult nudibranch dispersion

November 12, 1998
From: Jussi Evertsen

This message was originally sent to the Opisthobranch listserver at Steve Long's Opisthobranch webpage . As a reply Robert Bolland suggested that I send my message to the the seaslug forum as well. He has "seen the same thing with Berthella martensi, as well as in several other 'branchs on Okinawa".
So here it is:

I have a question about nudibranchiate dispersion based on many observations when diving and collecting nudibranchs here in the coastline of middle Norway (the Trondheimsfjord and Hitra and Frøya).

Is there any information about adult specimens dispersing by "planktonic behaviour"?

I have on many occasions observed Polycera quadrilineata drifting by when ascending from a dive. This species I have only seen doing this in the autumn and wintertime (from september/november to january/february). It seemed like they where drifting up-side down. When disturbing their floating around they would in many cases "fall down" towards the bottom, but only when disturbing the part pointing to the surface. It could seem like they had a mucous string from which they were hanging from. This behaviour has puzzled me a lot, since I have not yet read about this kind of thing with nudibranchs. I could in many cases also observe other bottom dwelling gastropods like Lacuna sp. also floating by.

Jussi Evertsen

MSc stud
Trondhjem Biological Station,
Department of Natural History,
Norwegian University of
Science and Technology,
N-7034 Trondheim
NORWAY
tlf: +47 73 59 14 89
fax: +47 73 59 15 97

jussie@stud.ntnu.no

Evertsen, J., 1998 (Nov 12) adult nudibranch dispersion. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/300

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