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The Emperor and the host living commensally

The Emperor shrimp, Periclimenes imperator is one of the most vivid and beautiful shrimps in the seas. A crustacean of the order decapods this palaemonid shrimp is a delight to behold and striking in it coloration.

Known from the shores of Africa to the Western Pacific it is a wide spread species that can be readily found in some areas by inspecting its common choice of symbiotic host.

The shrimp is commensal and lives commensally with many other reef creatures. The term commensal is derived form the Greek language and means that two animals live together with benefit to one of them but no apparent harm nor advantage to the other. The Emperor shrimp can be seen in such a commensal relationship with various nudibranchs and sea cucumbers. The most common hosts are:

Nudibranchs:

Chromodoris tinctoria
Hexabranchus sanguineus
Risbecia tryoni
Hypselodoris bullocki
Hypselodoris apolegma
Certosoma tenue

Sea cucumbers (Holoturians):

Holoturia fuscogilva
Stichopus variegates
Bohadschia paradoxa
Bohadschia argus

nudibranch hosting two emperor shrimp

Using eight of it’s ten legs for walking makes it very mobile on its chosen host. Indeed once located it is shy and very difficult to keep in visual contact with. It will race to the blind side of the host to keep away from predators or nosey divers whom it considers predatory.The remaining two legs are used specifically for feeding, sorting the detritus and waste found on its host for food and nourishment which is quickly passed to the mouth.

For protection it possesses a hard exoskeleton but normally prefers concealment and flight. On many sea cucumbers it prefers to graze the under parts of the animals making it difficult to see but on many nudibranchs it is readily visible unless hiding in the folds of the Spanish dancer.

As many nudibranchs are poisonous or noxious to predators it appears to be less cautious and is readily visible on their brightly coloured bodies. Whilst the Emperor shrimp comes in different colour forms it is not known if the shrimp can change its own colour form nor is it known exactly what advantages the shrimp garners from a specific colour form. Whilst the deep red colouration on a shrimp living symbiotically with a deep red Spanish dancer nudibranch could be considered camouflage it is not know why they choose other colours on different hosts which obviously do not provide a camouflage advantage in shallow waters on certain hosts. Of course at depth the colouration issue is mute due the natural removal of their prime colours, red and orange, from the visible spectrum.

The next time you are diving make sure to closely inspect its usual hosts. You may be pleasantly surprised with a glimpse at one of the animal’s most delightful residents.

Copyright 2006 Paul Whitehead. All rights reserved.

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Copyright 2006 Paul Whitehead. All rights reserved.

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