Rimicaris exoculata is the dominant decapod species found around hydrothermal vents. It is highly adapted to life in this ephemeral and unfriendly environment. It lives in close association with the warm areas of vents and uses the minerals and warmth of the hydrothermal fluids to 'farm' commensal bacteria which it grow on its highly modified gills. The characteristic lateral bulges of the carapace in this species are caused by the enlargement of the gill chambers. The chelae (claws) of R. exoculata are specially modified to scrape the bacteria from the gills. On my trip on the AMK I found a live copepod in the gut of an adult specimen. It is possible that, as with most shrimp, they are facultative opportunists.

The most interesting adaptation of R. exoculata is the presence of a reflective patch dorsally (the 'Dorsal Organ'). It has been suggested that this functions as an eye capable of seeing the far-red light emitted by hot hydrothermal plumes. However, studies by Cindy Van Dover using spectrophotometric techniques and our electrophysiological investigation (see my example publication for references) have suggested that this species, as with most marine crustacea, is best adapted to see light in the green/blue region. Since visual pigments which are maximally sensitive to light in the red regions of the spectrum have evolved in other species it seems odd that a putative far-red sensor is most sensitive to green light. It also seems odd that the 'eyes' of this shrimp are located on its back rather than at the anterior. What are they looking for??

The seething mass of shrimp found at the heart of a hydrothermal complex such as TAG is incredible to see. The shrimp appear as though they are continually struggling and fighting to get themselves into the best spot to feed their bacteria.

Rimicaris exoculata are by far the most abundant species around the vent but, occasionally a slightly larger shrimp, with a less obvious dorsal organ, stands out from the crowd. These were identified as another species,Chorocaris. Whether these feed on the more numerous Rimicaris is not known. Perhaps they scavenge dead or moribund Rimicaris, maybe cannibalism is not possible for Rimicaris by virtue of its highly specialised feeding appendages?

Away from the vent centre . . . .