Thanks Bernard,
Bill Rudman

Dear Chris,
I'm afraid not every weird shape is a nudibranch. I suspect this is a sponge colony. The pale band around the base, which looks like a foot, is probably part of the colony which was previously covered by sand. In future if you come across a strange object take a photo then give it a gentle prod to see if its attached. If it is not attached then by turning it over you may see some clues to what it is. Of course you should turn it back afterwards.

Any further mysteries - or non mysteries for that matter - from New Zealand are always welcome.
Cheers,
Bill Rudman

Dear Wade,
I hope Janine Collet can organise for the photo of Roboastra arika to be sent to the Forum. For that matter any records are of interest.

Concerning my discussion with Richard Willan. I was not suggesting that divers in the past had poorer observational skills than they have today. The problem is we have no systematically collected baseline data so we do not know if the apparent 'first appearances' of these tropical animals are in fact 'first appearances'. Many nudibranchs are notoriousy patchy in their distribution in both space and time. That is you can never rely on them being present at a certain place or at a particular time of the year. Most opisthobranch enthusiasts who have favourite places are always finding 'new animals' at their collecting spots even after years of visiting. You may be right in saying that more 'tropical' animals seem to be occurring at the Poor Knights now than 20 years ago, but unfortunately we have no way of knowing if this is really so. And even if it were so, we would have to ask whether the fauna 20 years ago was 'normal' or whether the present faunal composition is 'normal'? To know that, we would need baseline data from 50 or 60 years ago. It is interesting that records of tropical shelled molluscs from New Zealand in the 1800s were later dismissed as mislocalised specimens etc, but it is possible that in fact they were recording an earlier warm period.

The other point is that there are many more eyes out there and many more cameras recording things than ever before. While you and the hot young marine biologists were looking 20 or 30 years ago, most other divers then were only interested in what they could shoot with a spear gun, or collect and eat (paua, crayfish, sea urchins etc). As many nudibranchs have very short life cycles, sometimes only a few weeks, I am sure many visitations by transient tropical species could have occurred between visits by interested divers. From what I gather now, the Poor Knights would have diving parties visiting during much of the year, which must greatly increase the chances of animals being seen.

Unfortunately the lack of baseline data is a worldwide problem. Until we begin collecting faunal census data on a systematic and regular basis we will never be able to say with any scientiific certainty just what is happening to our fauna.

Best wishes,
Bill Rudman

Dear Cynthia,
To answer your question about the relationship between the NZ and SE Australian faunas. I used a recent checklist of NZ molluscs (Spence & Willan, 1996) where there are 138 opisthobranch species (excluding the pteropods) reported from New Zealand. After removing a couple of subantarctic animals and a couple of taxonomic anomalies I divided the remaining 134 species into 3 categories. Those endemic to New Zealand (NZ) those found in both NZ and southern Australia (Aust), and those found in NZ but having a broad distribution in the Indo-West Pacific (IWP).

You will see from the table alongside that there is a characteristic endemic NZ opisthobranch fauna, especially amongst the bubble shells and nudibranchs. There are species common to NZ and southeastern Australia, a phenomenon also evident in other marine molluscs, and a much larger element of species with a wide distribution in the Indo-West Pacific.

New Zealand has a rich endemic fauna of marine molluscs which to a large extent have evolved independently from the Australian fauna since the breakup of Gondwana. At present the prevailing currents in the Tasman Sea are from west to east which explains the occurrence of southeastern Australian elements in the NZ marine fauna. The widespread IWP elements in the fauna have probably been introduced both from Australia and from the large cyclic oceanic water movements which occur in the South Pacific from time to time (El Nino etc).

Thanks for mentioning Willan & Morton's handbook. It is certainly a good introduction, giving biological information on the species covered, but it is by no means comprehensive, dealing only with species that have been recorded from the vicinity of the marine station at Leigh. The other excellent book you mention, by Graham Edgar, includes a broad coverage of the temperate Australian marine fauna and flora, but as I explain above, the NZ fauna and flora is quite distinct.

Reference:
• Spence, H.G. & Willan, R.C. (1996) The Marine Fauna of New Zealand: Index to the Fauna 3. Mollusca. New Zealand Oceanographic Institute Memoir, 105 (for 1995): [Opisthobranchs on pp 32-37]

Best wishes,
Bill Rudman

Dear Katherine,
I'm afraid the New Zealand sea slug fauna is not big enough to justify its own book but if you are really serious the place to look would be:
Powell, A.W.B. (1979) New Zealand Mollusca: Marine, Land & Freshwater Shells. Collins: Auckland. 500pp.

Powell was an expert on New Zealand shells so he did not have a personal knowledge of the sea slugs. The opisthobranch section of the book was based on published information up until that date, and with discussions he had with experts in the field. It certainly will give you a good idea of the New Zealand fauna but I think it is now out of print so you would need to find a library which has it.

For photos, have a look in the Forum. If you go to the SEARCH facility and type in new zealand you will get a list of specific records to sea slugs from New Zealand on the Forum. Another place to look is Ian Skipworth's 'Skip's Underwater Image Gallery' which has some beautiful images of New Zealand Nudibranchs plus several other pages of underwater fauna, lots of links to other related sites - images, diving & equipment.
URL: http://www.ianskipworth.com/suig/index.shtml

If you have photos to identify, or specific questions, they are very welcome at the Forum.

Best wishes,
Bill Rudman

Thanks Richard,
Perhaps you could see if the divers who found these other two species would be willing to post their photos on the Forum so we have a visual record of their interesting find.

Your comments about global warming are interesting. The biggest problem with finding biological evidence of global warming is the lack of any baseline data. Divers have certainly been visiting the Poor Knights for some years but I suspect in earlier times most of them were more interested in hunting fish and collecting shells etc than in photographing nudibranchs, so we can't really say whether thse recent tropical finds are evidence of global warming or part of a fluctuating cycle which sometimes allows tropical larvae to reach northern NZ and survive.

You are familiar with Long Reef in northern Sydney. It is a relatively short reef but it sticks out from a headland that juts out into the sea, like an arm waiting to 'catch larvae floating past. I ran a search on the species of the cowry genus Cypraea which we had in our collection from Long Reef. In total there are 25 species represented, 24 of which are tropical in distribution. Anyone seeing the list would think that Long Reef was a shell-collecting paradise in the tropics. But no, it is a fairly rich temperate water reef with a smattering of temporary tropical species. At any time you might find one species of tropical Cypraea, but usually there would be none. The list is based on over 120 years or more of collecting, but without a scientific sampling program over the same period we have no way of knowing whether
Long Reef is becoming more tropical or not. I had thought of comparing the collection dates of all the specimens but I that would reflect the relative activity of collectors over time rather than give us any information on when cowry species were actually present. It is certainly an interesting topic.
Best wishes,
Bill Rudman

Dear Jane,
The most likely species you saw were Ceratosoma amoena for the orange-spotted one, and Tambja morosa for the black one with blue spots.

Have a look at the photos at the top of each species page, and at the messages below them for more information about these two.

However, you haven't given me an awful lot to go on so there is a possibility that I've got it wrong.
Best wishes,
Bill Rudman

Dear Ross,
Thanks very much for the photos which I will post on the site in the next few days.

I am interested in photos of any species from New Zealand, even things I already have photos of from Australia or elsewhere. The aim of the Forum is to provide not just an identification photo but evidence of a species' geographic range and its biology. So any of the animals you listed would be
great to have as they considerably extend the range of what are tropical or at least "Australian" species. Sea hares, side-gilled slugs (pleurobranchs), bubble-shells etc are all of interest as well as the true nudibranchs.

Your mention of photos with egg masses and mating are of interest as are photos of animals feeding etc so we can get some more information on what they feed on. If you can interest other divers in sending stuff it would be very welcome. If we get a bit of stuff I can set up a New Zealand index page so all the NZ stuff on the site could be readily found.

Concerning "pretty" versus "id" pics. I love pretty pics - unfortunately sometimes an id pic is needed as well to clarify things.

Thanks again,
Bill Rudman.