Jérôme Mallefet’s abyssal fishing


To draw up an inventory of the abyssal fauna; this was the ambitious objective of the Australian international mission in which Jérôme Mallefet participated. Over a month of intensive work in search of bioluminescent species was on the agenda. An interview.

If there is a fauna that remains largely unknown, it is the abyssal fauna, that is, that living between 2500 and 4000 metres in depth. It should be noted that it’s not easy to explore; it’s necessary to go to sea for several weeks with specialised equipment to reach it. These conditions didn’t discourage Dr Tim O’Hara of the Museum Victoria of Melbourne, who decided to set up the first Australian expedition devoted to the abyssal fauna; an opportunity that Jérôme Mallefet of the UCL Laboratory of Marine Biology didn’t allow to slip by! “ I have worked for years on bioluminescent animals and when Tim O’Hara told me that he would be the head of mission for this expedition I notified him that if there was a free slot I was up for it. Very little is known about deep-sea bioluminescence,” explains the researcher. “The abysses represent the largest ecosystem on our planet and not even 1% of them are known. There is already talk at present of mining ores from the seabed, while it’s not known what lives there... So there is a serious risk that this ecosystem will be destroyed before it has been studied.

So the researcher set off for the east coast of Australia, from Tasmania to the coral reef, for a 32-day mission with international taxonomists. The objective: to identify the species living there. “There were 27 scientists divided into two teams. Each team was on duty/scientifically active for 12 hours; the first shift began at 2 a.m. and went until 2 p.m., while the second shift worked the 2 p.m. - 2 a.m. time slot. This allowed work to be carried out continuously while we were at sea.

 Tasmanie - abysses - Mallefet         mission tasmanie - abysses - Mallefet

Extreme fishing

The first challenge in getting access to these sea creatures is sending collection equipment to depths ranging from one to four kilometres on a terrain that the researchers first had to map out. “It’s a bit as if you were in a helicopter between 1000 and 4000 m altitude and you sent a net 4 m wide to catch organisms on the ground blindly, or almost. In practice, to reach the bottom, 2, 4 or even over 6 km of cable must be played out. Imagine managing a net at 4 km depth that is 3 km behind the boat! It’s necessary to take account of the wind, the surface and bottom currents; in short, it was a real balancing act,” Jérôme Mallefet enthuses. To collect organisms living in various locations in the abysses, the researchers brought aboard several fishing tools:

  • a demersal trawl, a net 20 m wide that passes over the seabed,
  • a beam trawl 4 m wide that combs the seabed,
  • a sled with three cameras and lighting,
  • a second sled, called a Brenke sled, that collects the surface sediment,
  • a corer, a type of large box that sinks into the sediment and brings a quarter of a cubic metre of it back to the surface.
  • surface plankton nets.

As for me, I also brought a luminometer to measure the bioluminescence, a microspectrometer to determine the colour of the light emissions (the spectra), fibre optics and an ultrasensitive camera to document the bioluminescence.

Mallefet - microscope - mission Tasmanie                                            jérome mallefet

On the complexity of observing bioluminescence

A second challenge for the biologist was to successfully observe the light emitted by the abyssal animals! In fact, for this to be possible, it was necessary that the animals brought back to the boat be still alive, as light is produced in response to a stimulus. So it was necessary to be quick and observant! “As soon as the animals arrived in the sorting room I made my little tour, taking specimens still in good condition. I immediately put them in the dark, in seawater with sea ice. Once my “shopping” was finished, I isolated myself in a dark room set at 6°C in which I conducted all my experiments: first I stayed in the dark to allow my vision to acclimate as much as possible, and then I mechanically stimulated the organisms in order to be able to observe their luminescence and measure the maximum light by depolarisation. Finally, I attempted to take a photo of the bioluminescence.

Ophiure - bioluminescence - Mallefetbioluminescence - Mallefet     

Ophiure                                                                                                    Pennatule

bioluminescence - Mallefetbioluminescence - Mallefet

Holothurie                                                                                                         Octocorail

Identifying and analysing unknown species

During this expedition, Jérôme Mallefet observed dozens of light-emitting specimens, including numerous specimens he had never seen and about which very little is yet known. “The taxonomists of the expedition are going to deal with determination of the species, and now I am conducting biochemical, morphological and physiological studies of the tissue samples I brought back in the laboratory. I hope to shed some light on this abyssal fauna.

The researcher and his colleagues can already congratulate themselves on the diversity of their harvests, however: “The animals brought up are astonishing and surprising because they are very well adapted to the depths where they live. There was a red coffinfish with a lure on its head, batfish, tripodfish that rest on the rays of their fins on the seabed and await their prey, the famous faceless fish, a starfish over 50 cm in diameter, an anemone over 30 cm in diameter, a bright red spiny crab, etc. Each time the nets or devices were brought back up there were surprises! It was just fascinating; we all waited for the arrivals of the net on deck and we were just as enthusiastic the last day of the expedition as the first. It was a unique opportunity to be able to study this poorly understood fauna. I have studied bioluminescence at UCL for 30 years and I have never had access to these animals. The entire mission was extraordinary; I saw spider crabs emit blue light, brittle stars and starfish shine in green, in blue, bamboo coral produce a blue glow... It was magical. With the exception of three days of storms that kept us from working, there was not a day without living light,” Jérôme Mallefet concludes.

poisson sans tête - Mallefet Faceless fish
Red coffinfish

étoile de mer géante - MallefetStarfish

To find out more about the expedition.


Elise Dubuisson


A glance at Jérôme Mallefet's bio

1982 :             Bachelor of Biological Sciences (UCL)

1982-1988 :    Doctor of Science (UCL) with Prof. Fernand Baguet

1998-1990 :    FNRS Postdoctoral Researcher (UCL)

1989-1990 :    Postdoctoral Fellow, University of Montréal, laboratory of  Michel Anctil, Canadian government Fellow

1990- :            FNRS Research Associate, Laboratory of Animal Physiology (UCL)

1996- :            Part-time Professor (UCL) – Manager of the Marine Biology Laboratory

Published on July 25, 2017