Exploring the deep walls of the Coral Sea using rebreathers is opening up a new world to scientists and aquarists.

Heading away from the Australian coast the turbid inshore reefs give way to the rambling platform reefs of the mid shelf and then to the clear water of the ribbon reefs at the edge of the continental shelf.

But as we enter the Coral Sea the influence of the Australian continent falls away and the waters become truly crystalline.

Only outside of the Great Barrier Reef does the water fall away to oceanic depths. In these clear waters the reef keeps going and you want to follow it. But as many have found the urge to go deeper on air can be lethal. To overcome these limitations and to open up the depths to exploration, Cairns Marine has invested in re-breather equipment and training. This allows us to offer new, rare and unusual species in addition to our classic coral reef selection.

Mixed gas re-breather equipment is complex apparatus, consisting of two independent gas supplies. One of these contains pure oxygen, which is injected into the breathing loop to make up for the oxygen that is consumed by the diver.

The other gas supply is called the diluent, which consists of a special gas mixture such as Nitrox (nitrogen-oxygen, usually with higher than normal oxygen concentration than for compressed air), Heliox (helium-oxygen, usually with lower than normal oxygen concentration than for compressed air), Neox (neon-oxygen) or Trimix (usually helium-nitrogen-oxygen). Using this equipment is the fish collecting equivalent of walking on the moon.

Re-breather diving is "technical diving" - its expensive, hard work and not in any way glamorous. The equipment is cumbersome and awkward and this makes collecting difficult. However, the equipment allows our divers increased time at greater depth. There is increased risk that comes with monitoring complex equipment at depth but it allows divers to explore rarefied environments and to collect a range of species that are little known and some that are not known at all.

So let's go for a dive!

There is a sense of excitement that comes from knowing that on almost any dive you are likely to be the first human to have seen this part of the planet!

Along with this revelation comes discovery. The deeper you go the more likely you are to discover new species. At Cairns Marine we work closely with fish experts to document our finds. Biologists using conventional SCUBA have been limited to maximum depths of about 50m for productive exploratory work.

Scientific research using deep-sea submersibles has primarily focused on habitats at depths well in excess of 150m. The region in between is referred to as the undersea "Twilight Zone" and remains largely unexplored. Collecting fish at these depths allows researchers to learn more about species distribution and abundance that may have implications for resource management in the future. Exploring Coral Sea reef walls can be a dizzy experience.

Falling into the inky blue we pass the usual spectacle of utter beauty that only reefs can offer. Beyond 30 metres depth, the light becomes sombre. As we go deeper, the "light loving" corals give way to sparser cover and new types of fish. Divers encounter variable thermoclines and the temperature may decline rapidly in these areas, sapping energy from muscles.

Perhaps the greatest difference between re-breathers and conventional air based diving is the lack of noise. Re-breathers lack the racket of exploding bubbles that comes with SCUBA apparatus.

Down in the Twilight Zone the outrageous paint jobs on our re-breather casings seem quite comforting. Like guardians for the back of the mind.

Working at depths of 60 and 70 metres on steep walls is difficult unless you can find a ledge or platform. It seems these platforms are likely to be old coastal platforms cut into the wall of the reef at times of lower sea-level - still they do the job.

In the subdued light at these depths, fish that are considered rare in shallow depths are surprisingly plentiful and different. The implications are reshaping the way species abundance and diversity is considered. Exploring the Twilight Zone in the Coral Sea helps expand the known range of species.

World famous underwater photographer and experienced taxonomist Roger Steene says that diving to these depths in the Coral Sea is rewiring the record books for this part of the world. Cairns Marine is exploring these new frontiers to bring a broader marine experience to the aquarium industry and help science and aquarists to better understand life in our seas. Visitors to the Cairns Marine website who are interested in unusual species from the Coral Sea are invited to subscribe to the "Deep Lounge" newsletter, an occasional newsletter dedicated to the deep reef and Coral Sea news.

Resources

Randall J. E. and F. Walsh, 2008. A pictorial review of the Indo-Pacific labrid fish genus Pseudocoris, with description of a new species from the Coral Sea John E. Randall and Fenton Walsh: A pictorial review of the Indo-Pacific labrid fish genus Pseudocoris, with description Aqua: Vol. 14, Issue 2