This symbiotic relationship has already been demonstrated by a certain number of macro-invertebrates such as worms, echinoderms and bivalve molluscs. Moreover, in some of these animals, the digestive system is inexistent or has partially disappeared. Although it still has a functional digestive system, the abyssal shrimp Rimicaris exoculata belongs to this category of symbiotic invertebrates, as suggested by the presence of a large quantity of bacteria on the inner surface of the tegument of its branchial chamber. Julie Ponsard wanted to know if these bacteria served as a ‘larder’ for the abyssal shrimp, insofar as they are the main source of the organic molecules that the crustacean needs to survive and reproduce.

A miraculous catch 2,300 metres down!

Julie Ponsard’s demonstration began in 2007 when one of IFREMER's submarines went down to explore several of the Mid-Atlantic Ridge’s hydrothermal chimneys, especially the Rainbow site where our abyssal shrimp proliferates: an average of 2,500 individuals per square metre; it was just a matter of leaning over... At 2,300 metres deep, with the help of an articulated arm with a ‘vacuum cleaner’ attachment, the IFREMER researchers were able to take samples of living organisms, including Rimicaris exoculata. “The advantage of this organism”, Julie Ponsard explains, “is that it manages to survive the change of pressure when it’s brought to the surface. It’s therefore possible to carry out analyses on living animals." Once on board, the shrimps were nevertheless placed in a special aquarium that recreates the pressure conditions this crustacean is accustomed to; it lives with the weight of a two kilometres column of water above its head (approximately 200 bars).

(1) Inorganic carbon fixation by chemosynthetic ectosymbionts and nutritional transfers to the hydrothermal vent host-shrimp Rimicaris exoculata, Ponsard Julie et al., ISME Journal, 2012.