MV CHERTAN – Nov. 2002
UNDER THE BOAT
Neville Coleman/Copyright Neville Coleman
"Time and time again I am amazed at what fantastic rare and undiscovered species of sea creatures turn up under the boat, at the mooring line and around the anchor. During another MV Chertan trip around Milne Bay in November 2002 this 'law of nature' once again proved to be true."
MV Chertan camped at the jetty at Tawali Resort in Milne Bay. Since our trip the boat has been extensively refurbished, with a new engine and fittings. ( photo: Neville Coleman)
We were "camped" at Dinah's Beach tied up to the same coconut tree on the beach and anchored out by the stern into the very deep water. Exactly the same position every dive boat that camps at this famous dive spot has done for more than 20 years. Over this period hundreds of dive trips have resulted in thousands of keen divers in the world have dived here and they still return, many on a yearly basis.
So what makes this small piece of black sand slope and shallow boulder coral reef (one can swim along easily in one dive) so good year after year, decade after decade? I don't know if there is a single explanation. It's obvious that the cooler deeper currents bring along different life forms from a myriad locations each year. The slope affords hundreds of micro habitats at a range of depth and the river at one end provides rich nutrients and decaying plant matter every wet season.
One of my favourites are the Painted Anglerfishes Antennarius pictus which inhabit the area looking for all the world like small clumps of sponge on the sandy landscape. ( photo: Neville Coleman)
For the dedicated natural history explorer and photographer it is one of the most exciting frontiers in the Indo-Pacific. We were lucky this trip. Rob van der Loos had a very keen bunch of macro video exponents on board all shooting with the latest gear on a similar principle to how Rob shoots video himself. Everybody came up with exciting critters and we all couldn't help ourselves waiting to see the latest footage showing on the TV monitor at lunch and dinner presentations.
This mystery nudibranch turned out to be a colour varition of Striate Chromodoris Chromodoris striatella, 15m Milne Bay, PNG, Nov 2002. This species had not been found at this location before, yet a similar one turned up at Port Stephens, NSW. ( photo: Neville Coleman)
On one of Rob's tapes I noticed a nudibranch I was not familiar with and asked him where it was…"Under the boat at around 15 metres" was his reply. Next dive saw me idling down the slope with three cameras pulling myself along on my wrist knife so as not to disturb the bottom.
At 15 metres I put the SLR down on the sand behind an embedded rock and proceeded to swim in a search pattern, never losing sight of the camera. I found the nudibranch on a small patch of isolated reef at around 18 metres and worked on getting the pictures for the next few minutes.
The flashlight revealed the dead rocky reef was overgrown with a hard encrusting khaki sponge. I waved the coating of sand off, shone my torch onto the sponge and noticed a funny looking khaki lumpy "thing" burrowed into a hollow in the sponge. It didn't move when touched, felt hard and was to all accounts part of the sponge. However, something in my mind wouldn't let me leave, whatever it was it didn't appear part of the sponge and that could only mean one thing, "critter"!
Due to it's habitat and host it was once thought that this was a new species. On further study it has ben shown to be Cuvier's Slit Limpet Emarginula cuvieri. (15m Milne Bay, PNG, Nov 2002) This mollusc is host specific predator living on an unknown sponge, this is the first record of such an association of this family (Fissurellidae) of molluscs, as all other species are known to herbivores. ( photo: Neville Coleman)
No matter how hard I tried, the thing would not let go or move or give any indication it was alive. My mind went over all the things I knew to live on sponges and the only thing that made sense was an umbrella shell, but they had soft bodies and their shells sat on top of their body like an umbrella and I knew all the species. This was definitely something different.
All interest in the nudibranch dissolved while my endeavours were directed at discovering what sort of critter this was. After 15 minutes I was able to extract the lump without damage to it or me. Another 10 minutes waiting and its tentacles were in plain sight, the foot extended and mantle relaxed, it was definitely a mollusc and it appeared to have a shell on its back. The only molluscs with its general shape and structure were duck-billed limpets (Fissurellidae) but all the known species were algal grazers with black or grey bodies.
In my experience none were associated with sponges let alone sharing such an intimate relationship as I had uncovered. Once it was moving I managed a few pictures and moved up into the shallows. (Consequently the critter was first thought to be a brand new scientific discovery Emarginula sp. but several months later taxonomists found that it was very close to one that was already known).
20 metres – Under the boat
Maleta Luke as cook on the MV Chertan and one of the best 'critter' finders in the Milne Bay area. She has discovered many new species. ( photo: Neville Coleman)
After a couple of hours surface interval my next dive found me once again under the boat looking for another critter which Maleta had found for Rob for his video. At the very best this see-through yellowish-green diaphanous being looked like nothing in recognisable form, yet it crawled along the bottom. After 10 minutes I located it and tried to work out just what it was. There was no doubt it was some kind of opisthobranch but I had never seen anything this fragile looking. Being out in the open on black sandy mud it just looked like a piece of decayed algae. Although the photographs are nothing spectacular it appears that this "mystery being" is an undescribed species of Polybranchia sp. (See NUDIBRANCHS ENCYCLOPEDIA page 68).
Polygon Polybranchus Polybranchus sp. 20m Milne Bay, PNG, Nov 2002. Found by MV Chertan's cook and "critter" finder Maleta Luke. Another unique discovery for the trip. ( photo: Neville Coleman)
I looked further down the slope and saw a big yellowish sea cucumber with spots. It was a deeper water species which is generally only found on silty mud below 20 metres. After getting a few full frame shots I had a closer look and found it to be similar to a beautiful species of sea cucumber which I had first recorded at Lizard Island, Great Barrier Reef in 11/75. Many of the big tropical sea cucumbers have not been described as yet and some have been confused with others. (When I returned home I found that this species had just been described and published. The Ocellate Sea Cucumber Stichopus ocellatus which had always been a mystery to us for 30 years, now had a name! One down, only another few hundred to go……….
Although I had photographed and recorded this species in 1976 at Lizard Island on the Great Barrier Reef, it wasn't till 30 years later that it was described as a new species, the Ocellate Sea Cucumber Stichopus ocellatus. At below 20 metres at Milne bay it can be seen on the black sand slopes.( photo: Neville Coleman)
Four metres – Under the boat
Up in the shallows there are a myriad small rocks, coral nodules, rubble and coralline algae clumps to explore. One small rock was covered in red encrusting sponge and ever searching for the elusive Paron's sponge shrimp I eased over and checked it out with my torch. There were no shrimps but there in the middle of the sponge in a hollow was a nudibranch, the exact same colour as the sponge, even down to having its own sand grains in the pattern. It was incredible camouflage and no wonder I had missed the species on many previous occasions. (It has been identified as an undescribed species of Rostanga sp.).
Sand – speckled Rostanga Rostanga sp. 5m Milne Bay, PNG, Nov 2002. There are red and orange Rostangas throughout southern Australia and New Zealand all of which are associated with red or orange sponges. Tropical forms are not common.( photo: Neville Coleman)
On the underside of a rock on a small rockpile was a small (15mm) familiar-shaped and patterned critter that looks like a high-backed nudibranch. It was a Lamellarid. Lamellarids have internal shells and are related to cowries. (See page 61-62 2002 Sea Shells) and feed on ascidians. There are quite a few species of tropical forms which are undescribed. This was one with colour and texture unfamiliar to me and as such not appear in the scientific literature.
Furry Lamellarid Lamellaria sp. 4m Milne Bay, PNG, Nov 2002. These molluscs generally mimic the species of encrusting compound ascidians they feed on and due to this are very difficult to locate.
This beautiful litle Moon snail Naticarius alapapilionis It was found at night, gliding over the sandy rubble botom. Another sample of nature's 'Gems of the sea". ( photo: Neville Coleman)
Even though I have been visiting this site for over 20 years and have discovered scores of new species on previous expeditions, nothing compares to the number of new species found on the November 2002 expedition and at least half of these were found – under the boat. It's not difficult to discover new species. All it takes is time, initiative, an inquisitive nature, experienced eyes, a brain and a torch…all the rest is there. The Fun is in the Finding!
Even though year after year we would tie up at Dinah's Beach and see the large papery tubes sticking out of the bottom nobody bothered to find out what made them till Roger Steene mounted a quest and discovered it was a new species of huge bristle worm. It has since been named as Van der Loos Bristle worm Polydontes vanderloosi after MV Chertan's skipper.
Juvenile forms of Graeffe's Sea Cucumber Pearsonothuria graeffei are thought to mimic nudibranchs as form of defence and this form could certainly be mistken as one by a visual predator, or even some divers? ( photo: Neville Coleman)
Only seen at night the Sculptured Dendrodoris Dendrodoris sp. is an undescribed species well known at Dinah's beach Dive site. It may also be seen beneath dead coral slabs during the day. It has wine red spots and patches on the underside.( photo: Neville Coleman)