Chemical and thermal description of the environment of the Genesis hydrothermal vent community (13 degrees N, EPR)

The objective of this study is to describe the chemical and physical environment surrounding the vent organisms at the Genesis site (EPR, 2640 m). The main chimney is colonized by Riftia pachyptila, fishes Zoarcidae and crabs Bythograeidae. The top of the smoker is covered with tubes of polychaetes Alvinellidae, the frontier zone by limpet gastropods. Temperature measurements and water sampling were made on an axis along the chimney. The environment was characterized using relationships between chemical concentrations and temperature to provide a chemo-thermal model of the site. Discrete temperature ranges were 1-1.6 degrees C in sea water, 1.6-10 degrees C among Riftia plumes (up to 25 degrees C at the tube base), 7-91 degrees C close to the alvinellid tubes, fluid emission was 262-289 degrees C. This study describes the habitat of Alvinellidae emphasizing its chemical (Sigma S [H2S + HS- + S-2-] 3-300 mu mol l(-1), CO2 3.5-6 mmol l(-1), pH 5.7-7.5) and thermal specificities compared to the Riftia ones (Sigma S 4-12 mu mol l(-1); CO2 2-3.5 mmol l(-1;) pH 5.8-7.7). The size of Riftia allowed us to define its environment at the organism (temperature gradient along the tube 0.5-1 degrees C cm(-1)) and population scales (temperature difference between organisms from the same clump: 10-20 degrees C). Such spatial heterogeneity may play a significant role in the animal physiology and calls for further investigations.