Re: Chromodoris daphne from sthn Queensland

January 23, 2009
From: Denis Riek

Concerning message #22165:

Dear Bill,

Chromodoris daphne is also a frequent visitor to the Brunswick River northern New South Wales, Australia and the timing of its (and other opisthobranchs) appearances may indicate if it is a direct developer or, as you believe, lecithotrophic. I have seen at least half a dozen flood episodes in this small river since I have been recording the marine life in it and have observed that the repopulation always follows a constant pattern. Firstly I must say that nearly everything is wiped out in a flood with only the hardiest estuary species surviving and I dont believe that any slugs survive the fresh water and topsoil that pours out.

It usually takes about 3 months before the first slugs show up and they are always Austraeolis ornata and Jorunna sp 1. Plocamopherus imperialis then arrives on the main sea wall and Dendrodoris denisoni and Dendrodoris fumata show up further upstream. Sometimes Aplysia spp also arrive. It is always after these species establish that chromodorids appear about half a kilometre up river and always on the same rock wall. Chromodoris geometrica, Chromodoris daphne, Chromodoris cf reticulata and Hypselodoris obscura all appear about the same time and what is curious is that they are often large animals with almost no juveniles seen, and I have always had a thorough search before hand.

After this amount of time (about 4-6 months) all manner of species begin to show and it becomes difficult to establish a pattern but the diving rapidly improves!

If no slugs survive after a flood (chromodorids definitely dont) how do these species re-establish. The odd animal may come in on weed but the regularity of their arrival seems to indicate that they must have at least a short planktonic stage and can only establish once their food source is present. I have no qualification to make any assumption but I believe that my observation is correct so I would appreciate your opinion


Riek, D.W., 2009 (Jan 23) Re: Chromodoris daphne from sthn Queensland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Denis,

Thanks for this interesting account. We have similar catastrophic events in Sydney Harbour after extended periods of drought. Because of the nature of the harbour the sea water is not totally replaced by fresh floodwater but a layer of freshwater - perhaps a metre deep - overlies the seawater in the harbour and kills off all organisms attached down at least 1.5 metres. This destroyed a research project one time on different colour forms of the little direct developing chromodoridNoumea haliclona  killing both the slugs and their food sponges. It was some months before they returned intertidally and we assumed that as the slug was a direct developer, repopulation occurred from animals living deeper in the harbour.  River mouths such as the Brunswick River probably represent a different situation because the flood water I would assume, would replace all the seawater and kill all the organisms apart from the few hardy species you refer to.

In cases like this species with free-swimming larvae are probably the most likely to return quickly because their larvae are more capable of quich dispersal. The other thing to take into account is when the catastrophe occurs. Some species only reproduce once a year or for a short period duting the year. And some larvae are short-lived and some need months in the plankton to mature. So if the catastrophe occurs at the 'wrong' time it could be months before some species have larvae available to recolonise an available space. Some species, which are commonly called 'tramp species' seem to appear quickly whenever a space becomes available. There are a number of bryozoans which are good at that, and they often occur with attendant bryozoan feeding nudibranchs.

We basically need to know a lot more about the lifecycles of the nudibranchs and of the food organisms - algae, sponges, hydroids, bryozoans etc - before we can say much more about how nudibranchs re-establish themselves at certain places after catastrophes. It is a very interesting - if very complicated topic.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Jan 23). Comment on Re: Chromodoris daphne from sthn Queensland by Denis Riek. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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