Beyond the abyss

Snail fish

Swarms of snail fish - the latest images of life at extreme depth taken by the Oceanlab team

7 October 2008 by Alan Jamieson

Alan Jamieson and colleagues are on a mission to film the world's deepest-living fishes.

In 1843, the British naturalist Edward Forbes declared life was impossible below 300 fathoms (540 metres). This sparked a 20-year debate on the existence of a lifeless, or azoic, zone.

It was not until the 1940s that scientists resolved the depths at which life exists in the oceans. Marine researchers have split them into four distinct regions: the littoral (0-200m), the bathyal (200-2,000m), the abyssal (2,000-6,000m) and the hadal zone (6,000-11,000m).

For obvious reasons, the deepest of these zones remains the most inaccessible and poorly understood region in the ocean. Getting anything down to these great depths and surviving is a major technical challenge.

The anxiety on board was unbearable.

Much of the hadal zone is found in long, narrow and very deep trenches that form when tectonic plates collide. Most are found around the Pacific Rim and form a chain of trenches sometimes known as the Ring of Fire.

These trenches can plunge, at times quite dramatically, to nearly 11,000m, where pressures can exceed 1,000 bar (one ton per centimetre square).

The technological challenges that come with these extreme pressures means scientists have researched the hadal zone just a handful of times. This leaves a vast gap in our understanding of the oceans and marine life.

That is the backdrop to HADEEP, a project founded between the Universities of Aberdeen and Tokyo. We wanted to observe the transition between abyssal and hadal scavenging species, and any adaptations these creatures had made to survive at extreme depths.

Whale bones on seabed

A whale carcass becomes a ready meal on the ocean floor

The project, which only began in 2007, is as much an engineering challenge as a biological one. At the start of the project there were no instruments or vehicles anywhere in the world capable of descending to these depths. Moreover, we know that any animals inhabiting the hadal zone would certainly die if brought to the surface, meaning that any behavioural or physiological observations had to be done in situ.

A team of engineers at Oceanlab set about designing suitable technology that could withstand these enormous pressures. We worked closely with the biologists on experimental design to ensure we were giving them what they wanted.

We know that life in the deep-sea is very reliant on food sinking from the surface waters ('Whale Fall', Planet Earth Autumn 2007). There are two types of food: dead plankton and carrion such as fish carcasses.

Open ocean processes mean the quantity of plankton reaching the sea floor decreases with depth; food is extremely scarce in the trenches. But in principle, fish carcasses or 'food-falls' can happen anywhere and are independent of depth.

So life in the hadal is likely to be dependent on food-fall. We can exploit this dependency by using bait to attract animals in front of a camera.

In deep

The HADEEP team has many years of experience designing and operating free-fall lander vehicles. These machines descend to the deep-sea and ascend again unattached to the ship. We built two full ocean-depth-rated free-fall baited camera landers; one with a video camera and the other with a time-lapse stills camera. The next step was to get the landers beyond the abyss and into the hadal zone.

One of the packages made it with just one hour to spare

A generous offer of ship time aboard the research ship FS Sonne by the University Of Tübingen in Germany gave us our first opportunity to deploy the hadal landers. In July 2007 we joined the expedition to the Kermadec and Tonga Trenches situated between Samoa and New Zealand in the South Pacific.

To make the expedition in time, we had just six weeks to build the lander and eight weeks to sea-freight it to Apia in Samoa. One of the packages made it with just one hour to spare.

We spent three weeks at sea. During the expedition we successfully deployed the landers to 6,000, 6,500, 7,000, 7,500, 8,000 and 8,500 metres in the Kermadec Trench, and to 9,000 and 10,000m in the Tonga Trench. Free-falling autonomous landers into the deep sea is nerve racking at the best of times; the anxiety on board this time was unbearable.

On our arrival in Auckland, we packed up the landers and sent them on to Japan for the next part of the expedition later that year. In collaboration with the University of Tokyo's Oceanographic Research Institute (ORI) we deployed the landers in the Japan Trench to 7,000m from the RV Hakuho-Maru. We swapped ships a month later and dropped the submersibles 5,500m into the Marianas Region from the RV Kairei. A busy, but successful year by all accounts.

Deep sea fish

A grenadier, more commonly known as a 'rat-tail'

The images and data brought back from these expeditions were very exciting. Not to mention the pleasure and relief of proving our landers can survive the 10,000m descent - and perhaps more importantly, the ascent afterwards!

The footage showed massive swarms of small shrimp-like crustaceans known as amphipods. Surprisingly these creatures increased in numbers with depth. Most belonged to the genus Hirondellea, which is found throughout the oceans. Although we were amazed by the sheer volume of individuals feeding at the bait, this is what we expected to see at these depths.

What we weren't expecting to find were much larger lobsters, crabs and prawns, known as decapods. Before this expedition, marine biologists assumed decapods had no hadal representatives. On the contrary, at 7,000m we saw the decapod Benthescymus crenatus in relatively large numbers in both the Kermadec and Japan Trenches. These creatures were actively hunting small amphipods.

Another interesting find were macrourids, a conspicuous deep-sea fish more commonly known as grenadiers or 'rat-tails' at 7,000m in the Japan trench - 1,100m deeper than previously discovered.

Perhaps the most spectacular find was the liparid fishes. In the Kermadec Trench we found the liparid Notoliparis kermadecensis, a fish never before seen alive and had in fact only ever been caught once, in the 1950s. And if that wasn't exciting enough we found another liparid, again never seen alive before, called the Pseudoliparis amblystomopsis in the Japan trench, again at 7,000m.

The most spectacular find was the liparid fishes.

Both these fish are endemic to the hadal zone and we were lucky enough to observe both of them feeding and swimming in their natural habitat.

The next step for HADEEP includes further engineering developments and expeditions. The landers, fitted with temperature and depth sensors, inadvertently picked up some very interesting oceanographic data such as what appear to be approximately 12-hour tidal cycles. We have now upgraded them with custom-built salinity probes and water samplers.

Also, to complement the in situ observations, we've built a fish trap to bring some of these animals to the surface for taxonomic and genetic analysis. We trialled these upgrades in September 2008 onboard the RV Hakuho-Maru - the next Japan Trench mission. We will really put them through their paces in March 2009 during an intensive expedition to the Izu-Bonin Trench just south of Japan on board the RV Tansei-Maru.

So, in just the first year of the HADEEP project, we designed and constructed two full ocean depth capable lander vehicles, deployed them 11 times on three expeditions, discovered two different fish for the first time ever and broke four species depth records.

Dr Alan Jamieson is a marine engineer at Oceanlab, University of Aberdeen.

HADEEP - combining 'hadal' and 'deep' - is funded by the Natural Environment Research Council, with additional funds from the Nippon Foundation in Japan.