The mixing zone that Rimicaris exoculata frequent consists of hydrothermal fluid and the surrounding seawater is a complex and unpredictable microenvironment (Ravaux et al., 2003). The temperature ranges from up to 350oC at the vent opening to 1 – 2oC in the ambient seawater over a distance in the order of centimetres (Van Dover, 2000). Hydrothermal vent organisms have been recorded enduring high temperatures, such as the caterpillar worm (Hesiolyra bergi) that occupy the chimney walls and can tolerate temperatures up to 40oC, a more extreme example is the pompeii worm (Alvinella pompejana) that can tolerate high temperatures of 60 –80oC (Shillito et al., 2001; Ravaux et al., 2003; Schmidt et al., 2008).The sulphur rich superheated water emanating from the vents is utilised by the epibiotic bacteria that R. exoculata harbour for chemosynthesis. It has been demonstrated that optimal temperatures for carbon fixation are at moderate temperatures, epipbiont activity was recorded to be markedly greater at 20oC as opposed to 50oC (Ravaux et al., 2003). Initial studies that measured in situ temperature ranges of the areas at the TAG site occupied by R. exoculata ranged from 10 – 40oC, and up to 70oC several centimetres away from the shrimp swarms (Ravaux et al., 2003; Schmidt et al., 2008). The shrimp were observed jockeying for space, moving to another location after a matter of seconds (Van Dover et al., 1988).

Experiments have been carried out on live shrimp to determine maximum temperature they can tolerate (Ravaux et al., 2003). These experiments revealed that the upper thermal limit of R. exoculata does not exceed 37oC and above 40oC the shrimp would die. These figures suggest that the earlier in situ measurement were likely to have overestimated the shrimp’s tolerance range. Nevertheless, R. exoculata has exhibited adaptions in response to these fluctuations in temperature (Ravaux et al., 2003).

Read on to learn about the adaptations  – heat shock

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