New insights into life in the deepest places on Earth

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A feeding frenzy of cusk-eels where nothing was previously thought to live, an entirely new species of deep-sea fish, and large crustacean scavengers, are among the highlights of a recent research expedition that is shedding new light on the ecology of deepest places on Earth.

A team of marine biologists from the UK, Japan and New Zealand working within the HADEEP project have recently returned from an expedition to the Peru-Chile Trench in the Southeast Pacific Ocean on the German research vessel Sonne. There they used state-of-the-art deep-sea imaging technology to investigate life in the deepest parts of the oceans; the Hadal Trenches. The team used an ultra-deep free-falling baited camera system to take a total of 6000 images between 4500 and 8000 metres (three to five miles deep) within the trench.

These results revealed a high diversity and abundance of animals, mainly fish, at depths previously thought to be almost devoid of life. The HADEEP team has been investigating these extreme depths for three years, and two years ago filmed the deepest fish ever seen alive. Their previous findings from off Japan and New Zealand have revealed a strange phenomenon of snailfish (known as Liparids) inhabiting the trenches at a depth of approximately 7000 m, with each trench hosting its own unique species of snailfish.

To test whether this phenomenon occurred in all trenches they repeated the experiments on the other side of the Pacific Ocean off Peru and Chile, some 6000 miles from their last observations, and found that indeed there was another unique species of snailfish living at 7000 m. This species of snailfish is new to science and has never been caught or even seen before.

However this new species of fish was not the only significant find of the expedition. At 6000 m, a depth which previous campaigns had revealed to be a ‘no man’s land’, and where there had always been believed to be an absence of fish, they found more fish than all the other trench observations put together. Here, a species of cusk-eel (known as Ophidiids) aggregated at the camera and began a feeding frenzy that lasted the entire duration of the deployment; 22 hours.

The team leader, Dr. Alan Jamieson said, “These are some fantastic results and will prompt a rethink into fish populations at extreme depths.” He later quipped “We’ll be scratching our heads over this for a while, absolutely not what we were expecting.” He also added, “These results highlight the significance of the individual trench environment rather than simply depth itself.”

Dr. Toyonobu Fujii, a deep-sea fish expert from Aberdeen said, “How deep fish can live has long been an intriguing question and the results from this expedition has provided ‘deeper’ insight into our understanding of the global distribution of fish in the oceans.”

The activity of these fish was interspersed with the presence of scavenging crustaceans known as amphipods; large shrimp-like creatures of which one particular group, called Eurythenes, were generally far larger and occurred much deeper in this trench than found elsewhere. Many specimens of amphipods were collected by the team and are now in New Zealand.

Dr. Niamh Kilgallen, an amphipod expert working at the National Institute of Water & Atmospheric Research in Wellington said, “The sheer abundance of these big amphipods was overwhelming, particularly at 7000 and 8000 m, which is much deeper than they have been found in any other trench. It begs the question of why and how they can live so deep in this trench but not in any other.”.

These findings prompt a re-evaluation of the diversity and abundance of life at extreme depths. Furthermore, it is now apparent that each of the deep trenches hosts a unique assembly of animals which can differ greatly from trench to trench. The immense isolation of each trench draws parallels with island evolution theory popularised by Darwin’s finches.

The HADEEP project is funded by the Nippon Foundation (Japan) and NERC (UK) and is a collaboration between the Universities of Aberdeen (UK) and Tokyo (Japan) with additional support from NIWA (New Zealand).

For comment, contact:

Dr. Niamh Kilgallen,

NIWA (New Zealand)

Dr. Alan Jamieson,

University of Aberdeen

(UK) 00 44 1224 274410,

a.jamieson@abdn.ac.uk

Dr. Kota Kitazawa,

University of Tokyo (Japan),

Email: kitazawa@aori.u-tokyo.ac.jp

Other contacts:

Jennifer Phillips

University of Aberdeen Press Office

Tel:  00 44 1224 273174,

 j.phillips@abdn.ac.uk

Dr. Toyonobu Fujii

University of Aberdeen deep-sea fish expert)

Tel: 00 1224 274430,

t.fujii@abdn.ac.uk

Diversity in the Deep
Research subject: Benthic habitats