Caridean shrimps, belonging to the family Alvinocarididae,

dominate the vagile megafauna at most Mid-Atlantic Ridge hydrothermal vent sites (Desbruyères et al., 2001). One species, Rimicaris exoculata (Williams and Rona, 1986), is particularly abundant, forming dense swarms (>3000·individuals·m–2) around the chimneys expelling superheated sulfide-loaded fluid (Segonzac et al., 1993; Polz et al., 1998; Gebruk et al., 2000). This species supports a highly specialized bacterial epibiosis within its gill chamber, which constitutes the major, if not unique, diet source of R. exoculata adults (Casanova et al., 1993; Gebruk et al., 2000). The epibionts are believed to be chemoautotrophic sulfur-oxidizers (Wirsen et al., 1993), and mesophilic temperatures (>20°C) have been suggested to be important for carbon fixation (Wirsen et al., 1993; Gebruk et al., 2000). Whatever the reason may be for maintaining close proximity to hydrothermal flui