When people first discovered that hydrothermal vents sustained entire ecosystems thousands of metres beneath the sea, incredible claims were made about the creatures that flock around the superheated waters; they seemed capable of surviving at temperatures that most surface creatures couldn't endure. But Bruce Shillito wasn't sure that it was that simple; after all, thermal gradients close to a smoking vent are very steep, maybe vent fauna weren't getting quite as hot as everyone thought. Working with Juliette Ravaux and a team from the Ifremer Research Institute, he travelled to the Rainbow vent in the Atlantic Ocean, to gather shrimps and watch the crustaceans' reactions to warm water. But instead of recording an all-time high-temperature survival rate, the shrimps tried to flea as the temperature rose, and more surprisingly, none survived above 43°C (p. 2345); which is lower than many desert animals experience on a daily basis!
Safe on the surface, the team directed a remote operated vehicle towards the crustaceans gathered at the vent, sucking them up into boxes for transport to the surface. The shrimp seemed unaffected by the enormous pressure drop as they ascended, and once at the surface the team transferred the crustaceans to specialised aquaria where they were pressurised to 230 atmospheres. Shillito explains that `one thing we were really conscious about... before we tested anything on these creatures, was that they were healthy after collection, and repressurising' so he and his colleagues measured the crustacean's metabolic rate over a period of hours to insure the shrimp's fitness. Surprisingly, the pressurised shrimp's metabolism was remarkably similar to other crustaceans of a similar size. And by inserting an endoscope through the top of the pressure vessel, Shillito could see that the shrimps seemed undisturbed after transfer to the tank. Convinced that the shrimp were relatively unaffected by the ascent, he began to see how they reacted as the temperature rose.
But it soon became apparent that the animals were not comfortable in hot water. First they tried escaping from the warm current as the temperature rose, losing the ability to swim at 37°C, and none survived when the temperature rose to 43°C. When the team repeated the experiment by slowly increasing the temperature to 25°C, the crustacean's activity increased again, but this time, they survived.
Back in the Paris at the Université Pierre et Marie Curie, Shillito and Ravaux wondered how the shrimps protect themselves from high temperatures. Had the shrimp developed a suite of heat shock proteins to defend themselves from rising temperatures, or had they evolved a specialised mechanism to protect themselves from overheating? Ravaux tested the crustaceans that survived the mild heat shock, and found that the shrimp had begun producing a protein that was very similar to the heat shock protein, Hsp70.
Hsp70 is known as a `rescue protein', protecting cellular proteins from degradation as the temperature rises, and Ravaux suggests that `this probably means that the temperature exposure is beginning to be a problem, and probably sets the shrimp's thermal limits even lower than 25°C'. So how do the crustaceans survive so close to the vent's superheated waters? Shillito suspects that, protected by their heat shock proteins, they can dart into jets of hot water just long enough to collect the toxic hydrogen sulphide that the shrimps need to survive, before retreating to safety.
- © The Company of Biologists Limited 2003