Voyage to the bottom of the Bight

By Mary O'Callaghan 4 December 2017 7 min read

AS the net is winched aboard the research vessel, the scientists gather round, anxiety quickly turning to relief and excitement as they see that it is not empty—it has taken 5 hours to get the net to the bottom of the Great Australian Bight 5000 metres below, tow it across the seabed to collect the sample, and bring it back up again.

Best known deep-sea region in Australia

In November–December 2015, over two back-to-back voyages on board the research vessel RV Investigator, the 40-strong team of scientists collects more than 63,000 specimens, representing 1073 species—including, it turns out, a whopping 277 species new to science.

The sampling is part of the first ever systematic study of the deep-sea floor of the Great Australian Bight, conducted under two separate programs, which agreed to share their data: the $20 million 4-year Great Australian Bight Research Program—a collaboration between BP, CSIRO, the South Australian Research and Development Institute (SARDI), the University of Adelaide and Flinders University which finished in November; and the Great Australian Bight Deepwater Marine Program—a collaboration between Chevron and CSIRO which concludes in 2018.

On board both voyages, running the operations and spending a marathon 69 consecutive days at sea, was CSIRO scientist Dr Alan Williams. He explains the importance of the research: “From a benthic ecology perspective, this research has transformed the Bight from one of Australia’s most poorly known deep-sea regions to the best known.”

Lanky spiders and cock-eyed squid

As well as the new species, the team found many rare species, with one third of all species known only from single specimens. And of the 350 species previously recorded in Australia, 164 were not previously known to be present in the Bight, highlighting the lack of sampling in the region.

These are mostly small animals—food is generally scarce in the deep sea, and of poor quality. “The deeper you go, the worse the food situation gets,” explains Alan Williams. “Most food is produced near the sea surface and is consumed several times in the food chain as it descends to the seabed. We catch the occasional large scavenging fish—they feed on carcasses of large fish or mammals that fall rapidly from surface waters—but, typically, the animals are small.”

Small is relative. “We caught some large sea spiders with long, gangly legs, measuring up to 60 cm across. These giants belong to the genus Colossendeis; we collected six species, one of which is almost certainly new. Sea spiders are capable swimmers, treading water rapidly to lift themselves into the water column where they are carried, spread-eagled, by slow-moving currents over vast distances.”

Despite living in total darkness, the cock-eyed squid (Histioteuthis miranda), dark red in colour, has a giant left eye. “It’s an active predator of fish, crustaceans and probably other squid, and it’s thought that the big eye can operate in low light. Gazing upwards, it can see its prey silhouetted against the faint light from above.”

Thousands of gelatinous, purple blobs swimming sedately just above the sea floor was a sight to capture the imagination, says Alan: “These sea cucumbers (Enypniastes eximia) were a lovely purple colour but what was extraordinary was how many there were. They seem to aggregate 5 metres off the seabed, swimming along, filtering out phytoplankton.”

Collecting samples – a long haul

Planning exactly where on the seabed to take the samples was part of Alan’s job.

“The first thing we do at a new location is make a map of the seabed using a multibeam sonar, which is just a fancy echo sounder. We make most impressive seabed maps and we use them to work out different habitats. In the deep sea, a lot of the sea floor is flat, muddy plains of sediment but there are also rocky outcrops, canyons, and seamounts, which are undersea mountains.”

A mix of nets are used to collect samples from just above the surface of the seabed; a core sampler is used to collect sediment from the seabed.

“The beam trawl is 4 metres wide and half a metre high,” explains Alan. “It’s like a stocking on a metal frame. It’s attached to a tow wire and we pull it along the bottom. At some of the deepest sites, over 5000 metres, we had 7.5 kilometres of tow wire out.

“My job was to make sure that when the device hit the bottom, it hit in the right place, it stayed on the bottom, and it came off at the right place. With a combination of geometry and timing, we can calculate how much wire to put out and how fast to put it out while the ship is moving forward.”

ID please, and fast

Figuring out what species have been collected in the samples is a two-phase process that starts on board the ship.

“We had a team of taxonomists onboard so we were able to do a very good first pass over the collections and identify them at a good level,” says Alan. “One of my team, Karen Gowlett-Holmes, is like a walking encyclopaedia of marine animals. She’s also a photographer so she photographs everything.”

The scientists worked daily 12-hour shifts. “Most people worked even longer hours,” says Alan. “It was a total marathon of working effort.”

This type of work is an ecologist’s dream. “We had a Russian scientist on board, working on worms,” says Alan. “She was looking at some specimens on a glass dish under the microscope. ‘How’s it going’, I asked. ‘Actually, I am in heaven’, she said. She had never before had live specimens of this rare group—only preserved ones, dead and somewhat dishevelled.”

All the specimens were preserved onboard, in alcohol or formaldehyde. Back ashore, they were taken to the lab and those needing formal identification were sent to a network of specialist taxonomists, mostly associated with museums, who provide authoritative identifications.

“We sent some to Poland, some to the US, some to New Zealand. We had more than 25 people in that process.

“We preserve the specimens in groups. So, for example, we put all the sea spiders in the same barrel and that barrel goes to the sea spider specialist.”

It typically takes weeks to months for a specimen to be formally identified. With tens of thousands of specimens to be examined, Alan is proud that the entire collection was identified within 18 months: “We ended up with very rigorous identifications. The rigour and timeframe make for an impressive feat.”

30-year identity crisis

One creature whose identity had been in question since 1986, when it was first described, has finally received some closure.

Dendrogramma was hypothesised as being a missing piece of the animal kingdom jigsaw puzzle, but the specimens at the time couldn’t be DNA tested because of how they had been preserved. The intriguing, scientific mystery was solved last year when Alan’s team found more specimens.

“We were able to throw the most modern genetic techniques at our specimens and found that they were pieces of a complex animal, but from a known animal group. So we proved that it’s not the missing link, though it’s still weird and interesting.

“Dendrogramma is a siphonophore—a kind of jellyfish but attached to the seabed, like a parachute held down with numerous ripcords. The pieces we collected are like protective discs. It’s soft and delicate which is why you never see whole ones.”

Oil-loving bacteria

Using ‘next-generation’ molecular sequencing technologies, the researchers were also able to show that a variety of oil-loving bacteria live in the Bight. “Although it is difficult to conceive, about half of the oil that spilled from the Deepwater Horizon in the Gulf of Mexico in 2010 was consumed by bacteria,” says CSIRO scientist Dr Sharon Hook. “There is high interest about the potential of bacteria in the Bight to respond in a similar way if oil and gas exploration and production proceeds in region in the future.”

This research will lead to the development of a sensitive tool for rapid ecological monitoring. One day, it may be the smallest of organisms that are first to signal changes in the deep waters of the Bight.