JAMES CAMERON knows how to make a splash. Literally. On March 25th the director of “The Terminator”, “Titanic” and “Avatar” plunged into the Challenger Deep of the Mariana Trench, 500km (300 miles) from Guam. When he reached the bottom, he sent a self-congratulatory tweet, and then tootled about for a couple of hours before taking Deepsea Challenger, his lime-green one-man submarine, back up the 11km to the surface.

This venture certainly scores high in the jaw-dropping department. The only other people to plumb the Challenger Deep—as its name suggests, the most profound point in the ocean—were Jacques Piccard and Don Walsh, who did so in 1960, in a vessel called Trieste. The latest dive, however, was not very successful on the scientific front. It brought back no specimens.

This was in sharp contrast to a less publicised mission, to the paltry depth of 2.5km, where the pressure is a mere 250 times that of the atmosphere (the Challenger Deep's pressure is four times that). This was organised by Ifremer, France's oceanographic institute. Its three-man craft, Nautile (named after the submarine in Jules Verne's novel, “20,000 Leagues under the Sea”), not only brought back samples, but brought them back alive.

That is no mean feat. Because creatures of the deep ocean have evolved to tolerate so much pressure, their cell membranes tend to liquefy when that pressure is released. To stop this happening Nautile's samples were transported in a special chamber called PERISCOP. This chamber, designed by Bruce Shillito and Gerard Hamel, of Pierre and Marie Curie University, in Paris, is a tank with a capacity of 2.7 litres which is capable of containing a pressure of more than 200 atmospheres.

In 2008 PERISCOP was used to reel in a live fish from a then-record depth of 2.3km. The fish had been living near an underwater hot spring, known as a hydrothermal vent, in the Mid-Atlantic Ridge. This time, Nautile's mother ship, L'Atalante, had spent three weeks trawling around a similar vent in the East Pacific Ridge as part of the MESCAL project, a collaboration between a dozen American and European oceanographic research institutions. On March 26th she sailed into Manzanillo, in Mexico, bearing a trove of specimens including a dozen or so Pompeii worms. These polychaetes (relatives of the common ragworm) are the most heat-tolerant animals known. They are able to live at 60°C. Biologists would like to understand how they do it.

To help them find out L'Atalante has been fitted with a second chamber, BALIST, into which PERISCOP's catch can be transferred. Researchers on board ship were thus able to study the worms alive for several weeks. For the unfortunate worms, however, Manzanillo was the end of the line. They were killed, frozen and transported back to France.

Future trophies may be luckier. Ifremer's researchers are searching for a way to keep deep-sea animals alive indefinitely, so that their entire life cycles can be studied. This means building high-pressure, onshore fish tanks. On April 7th the Océanopolis, a big aquarium in Brest, will unveil two such chambers. Each Abyss Box, as the contraptions are known, costs €100,000 ($134,000) and contains 16 litres of seawater held at 180 atmospheres. Crucially, each has a window: a glass visor 15cm across and 8cm thick.

At the moment, one of the boxes is inhabited by 43 deep-sea shrimps. The other houses three crabs. Both come from Atlantic vents located around 1.8km below the surface. It will be the first time members of the public who are not James Cameron have had a chance to behold such creatures alive.