The Twilight Zone is a hitherto unexplored area of the sea too deep to be dived and explored using regular SCUBA gear, but not deep enough for submersibles to be considered worth employing.  It is the in-between zone ranging from 40 - 150 metres (m) which, thanks to recent technical diving technology, can now be accessed by specially trained divers using unique and complicated diving gear. 

Penetrating depths of the sea never previously explored is both intensely fascinating and a bit scary.  It is fascinating and exciting because there are flora and fauna that human beings have never worked with intensively before.  The divers of IUI are literally breaking through the frontiers of science, exploring a region that no one has ever had more than fleeting glimpses of at best.   While there have been brief excursions into the Twilight Zone before, only now has it become possible to stay for extended periods in order to make quantitative measurements, do extensive species collection, and conduct in situ experiments.  It's a mind-blowing prospect, being the first ever to do certain things!

It's also a very valuable one to science.  "There is almost no current knowledge on fish, coral, and other invertebrate communities in the deep coral reefs of the region.  All scientific knowledge and conservation oriented decisions are based on data from shallow water," to quote IUI's head diving officer, Oded Ben Shaprut.   Yet, the reefs at these depths are teeming with life and live coral cover. 

Several possible new species have already been discovered by researchers Eran Brokovich and Shai Einbinder, and are presently undergoing the process of verification.  Some species may be completely unknown to science, while others may be ‘new records', meaning the first discovery of a species that exists but has never been found in a particular geographic area, as with the coral Euphyllia paradivisa submitted by Shai.  The researchers have reason to believe there are probably many more new species or records to be found, as Dr. Avi Baranes has written up 12 news species of fish that had been fished from depths of 200-800 m, as well as a moray eel fished from 150 m which is right within the Twilight Zone.  To quote a pioneer in this field, Richard Pyle of the USA, "Over 50% of all fish collected at depths greater than 45 m were unidentified.... Seven new species per hour of diving..."

A surprising and rather amazing discovery in the Twilight Zone is that species already known in the Gulf of Eilat may appear at deeper depths with a whole different societal structure, distribution, or morphological structure than their shallower counterparts.  The grouper (Epinephelus fasciatus) has always been known as a fish that is solitary in its habitat.  In 50 metres, however, the groupers were discovered living in social groups numbering hundreds!  The groupers do actually group, it seems! 

The Zebra Angelfish (Genicanthus caudovittatus) is seen only as adults above 30 metres, and even at 50 metres very few younger fish are seen.  Only at 65 metres were vast populations of juvenile angelfish found.  An article by Eran shortly to appear in Marine Ecology Progress Series describes an extended depth range of 48 reef species, all found in a region never able to be explored until two years ago.  The differences within a familiar species may also be structural:  The coral Stylophora pistillata was found at depth to have fewer polyps and less defined septae (‘dividers') than the ones known from shallower reefs. 

‘Matrix' - MTRX - is the name the InterUniversity Institute (IUI) has given its Marine Twilight Zone Research and Exploration programme, led by senior diving officer, Oded Ben Shaprut.   The IUI, located on Eilat's South Beach, is one of less than ten institutes in the world exploring the twilight zone and is one of, perhaps even ‘the', leader among them.  Institutes such as the Hawaii Institute of Marine Biology or the Caribbean Marine Research Centre are also engaged in similar exploration, but IUI is fortunate to remain on the forefront of diving technology and hence ever-expanding research opportunities.

The risk in this deeper sea exploration is not due to giant squid or sea monsters lurking down there in wait of their lunch, but due to the complicated array of breathing gasses that must be employed and their proportions balanced accurately at every given depth by a computerised system.  The physics of diving, specifically the effect of pressure (depth) on the gasses being breathed and their effect on the body as a result, require precision control.  Any mistake or malfunction can potentially lead to disaster.   

The first technical diving mixture employed was Nitrox, which has a higher oxygen and lower nitrogen content than air.  This gas mix, used by tens of people at IUI nowadays, is good down to 40-42 m.  Beyond that depth the partial pressure of the oxygen starts becoming too toxic. 

The next gas mix to be adopted, in 2005, was Trimix, which replaces part of the nitrogen and oxygen of air with helium, another inert gas.  As oxygen is toxic at 60 m. and the more nitrogen you're breathing, the more subject you are to narcosis at depth and the ‘bends' upon ascent, reduction of these gasses in the breathing mix allows for far greater depths and/or bottom times.  Approximately ten IUI divers are trained in the use of Trimix.  Trimix, however, is very expensive and one dive can cost hundreds of shekels.

The newest innovation to broaden IUI's diving and research capabilities is the rebreather, introduced at the end of 2006.  This technique uses a gas mixture and a filter, basically recirculating the gas between the diver's breathing and the apparatus but at finely tuned proportions.  Unlike Trimix, where other mixes known as ‘travel' or ‘stage' gasses are used on the way down and the way up (including decompression stops), the rebreather requires only the addition of a ‘bailout gas' tank.  The rebreather allows extended time on the bottom while using little breathing gas, as well as for a very efficient decompression regime.  Plus, it's much cheaper per dive.  However, its use requires very intense training and only four IUI divers are presently qualified in its use.  An instructor was flown from the USA specially to train them in it.  Now, for the first time ever, there will soon be a rebreather instructor in Israel, as Oded Ben Shaprut is being sent next week to the  USA to undergo instructor training at the Megalodon institute.

Over 20 IUI students have been trained in one or more of the technical diving techniques.  Over 1000 dives between 40 - 100 m. have been made by IUI divers.  15 publications have already been produced just in the short time that exploration of the marine Twilight Zone has been possible, and vast opportunities for research still abound in the mysteries beneath the sea.