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New bone-stripping crustaceans discovered from the deep-sea

By: Dr Niamh Kilgallen, Category: Science, Date: 21 Jul 2014

Exploring one of the most poorly-understood ecosystems reveals amazing new species that can teach us about life in their extreme environment

Hirondellea wagneri

Milly Sharkey, University of Bristol © Milly Sharkey, University of Bristol

Scientific exploration of the deep ocean is increasingly vital in developing conservation practises for an area fast becoming more accessible to mineral and petrochemical exploitation, and the fishing industry. Recent scientific expeditions have resulted in the discovery of some very interesting deep-sea species indeed.

Meet Hirondellea wagneri, a lysianassoid amphipod from the Peru-Chile Trench. At just 13 mm long she may not look particularly menacing, but don’t be taken in by her small and harmless looking exterior. In a previous blog I described lysianassoids as vultures in a small, shrimp-like disguise. So think of vultures. Now think of that Hitchcock classic “The Birds.” This girl and her buddies will gang up on you and strip the flesh from your skeleton in a matter of hours. They have voracious appetites and are quick to vacuum up the remains of any carrion that they come across.

Luckily for you, your chances of encountering Hirondellea wagneri are pretty slim given that they live more than 6 km under the sea surface, in the deepest and most inaccessible part of the ocean known as the hadal zone. This is the area of ocean below 6000 m in depth, named after the realm of Hades, the mythological Greek underworld. 

Hirondellea wagneri is just one of three new species of this wonderful genus that I have recently described, all from the same ocean trench. The other two, H. sonne and H. thurstoni live at even greater depths, more than 7km and 8km beneath the sea surface, respectively. Their near relative, Hirondellea gigas is famous for living at the deepest known place on earth, the Challenger Deep in the Marianas Trench, 11kms beneath the ocean surface. They even caught filmmaker James Cameron’s eye during his record dive there in 2012. Few other animals are capable of thriving at such depths, where the pressure is over 11270 tonnes per square meter. To put that in context, a male white rhinoceros averages about 2.3 tonnes, so the pressure that H. gigas lives under is roughly equivalent to that exerted by 4900 rhinos standing on a diving board!

For me, it is the depths at which these animals live that make them so interesting to collect and describe. It is a privilege to study something so exotically inaccessible. These three new species were collected in 2010, when I had the great fortune of participating in a research cruise aboard the German research vessel Sonne, which departed from Guayaquil, Ecuador, and spent three weeks steaming the length of the western South American coastline as far as Valparaiso, Chile. In that part of the world the oceanic Nazca tectonic plate subducts beneath the less dense continental South American Plate creating a V-shaped trench that hugs the South American coastline for about 5900 km, lying about 160 km off the coast, and plummeting to 8065 m at its deepest point.

It is not an easy task to sample at those depths. For the purposes of collecting physical samples and other data, a specially designed autonomous hadal lander was used. The lander itself consists of a 2 m high aluminium tripod with an array of attached scientific equipment, and buoyancy modules connected to a mooring line. Typically, the scientific equipment comprises a CTD (conductivity, temperature, depth) sensor; baited traps for capturing small invertebrates; and a waterproof camera designed to withstand the extreme water pressure. The camera is mounted on the lander frame and pointed towards the sea floor, taking photographs at 1 minute intervals for the duration of the dive. Bait is used to lure fish and large invertebrates into the camera’s field of view. Before each deployment steel ballast weights are attached to the lander frame, the camera is switched on, and then the whole structure is deployed overboard and sinks slowly to the sea floor. Once it reaches the sea floor it remains stationary for 12-24 hours, recording data such as temperature and pressure, photographing animals attracted to the bait, and capturing anything that swims into the traps.

At the end of the sampling period, the lander is retrieved by commanding an acoustic release system to drop the ballast weights via a signal sent from the surface. Once the ballast weights are dropped the lander becomes positively buoyant and begins to float upwards at a rate of about 2000 m per hour. The first few minutes are nail-biting, until the lander returns an acoustic signal to the surface, confirming that it is indeed ascending. Previous landers have been lost forever at sea through the ballast being unsuccessfully jettisoned. Fortunately, there were no such mishaps on the Peru-Chile cruise!

It is often said that we know more about the surface of the moon than we do the deepest parts of the ocean. In 2010, we deployed the lander 5 times to the floor of the Peru-Chile Trench. We discovered these three new species of Hirondellea, in addition to the other new amphipods, and a new species of snailfish that are yet to be published. We only gathered data about animals that were attracted to the bait (scavengers, or predators attracted by the scavengers), or animals that happened to wander into the field of view of the camera. The field of view of the camera is 0.29 square meters. The Peru-Chile Trench covers an area of 590, 000 square kilometres. Imagine what else is down there.

Dr Niamh Kilgallen
Scientific Officer

More information:
Kilgallen, NM (2014) Three new species of Hirondellea (Crustacea, Amphipoda, Hirondelleidae) from hadal depths of the Peru-Chile Trench. Marine Biology Research, 1–15, DOI: 10.1080/17451000.2014.889309

The expedition to the Peru-Chile Trench was undertaken as part of a project called ‘HADEEP’ (HADal Environment and Education Program), and involved a team of scientists from the University of Aberdeen and the University of Tokyo. The purpose of HADEEP was to explore the biology of life at extreme depths in our oceans using new technology designed and operated by the project.

Tags Amphipoda, Crustacea, hadal, Lysianassoidea, new species, Peru-Chile Trench,