One of the fascinating things about the underwater world is that no matter how closely you look at something, you can always be surprised by what is living down there.
A sea cucumber or urchin might seem like something worth ignoring by most divers, however our dive guides know that it needs a closer look, because who knows what is living on it!
When you start looking at the mundane things in closer detail, a whole new world will begin opening up to you. Today, we will be talking about the emperor shrimp – a small, yet fascinating species of shrimp, that might not be particularly rare, but is often overlooked by divers who are in a rush to get to the ‘more interesting things’.
Emperor Shrimp, scientifically known as Periclimenes imperator, are a small species of commensal shrimp that are part of the larger family Palaemonidae. They are regular sightings for us in Bunaken Marine Park, however they can also be found throughout much of the Indo-Pacific.
A fully grown Emperor Shrimp measures less than two centimetres from head to tail, but being small is necessary when you spend your life hitching a ride on someone else’s back (or belly, or gills…). They can be easily identified by their orange sides, white back which is flecked with tiny orange dots, and orange claws that are tipped with purple.
They are one of many different species of ‘Commensal Shrimp’, meaning that it forms a symbiotic relationship with at least one other species.
Commensalism is a symbiotic relationship where one party involved benefits from the relationship, while the other (or others) receive no benefits, nor do they come to any harm. An easy land example of this would be a spider building its web on a tree. While the spider is benefiting from having a place to build and hide, the tree is getting nothing from this arrangement, however it is also not suffering in any way.
An emperor shrimp is never spotted on its own.
It will always be hitch hiking on the back of a much larger, slow moving species of Holothurian (the scientific term for sea cucumber) or one of the larger species of Nudibranch, such as the Spanish Dancer (Hexibranchus sanguineus). It is more common to see a single emperor shrimp on a host, but if you keep an eye on the host you may spot a second shrimp hitching a ride. When there are two shrimps on a single host, they will often fight over who gets the best foraging turf – which is usually either around the mouth, or the anus.
The shrimp will live on the host’s surface, which provides it from sanctuary from the many dangers of the ocean. Should any potential predators appear, the shrimp will simply disappear underneath its host, or in other hard to reach places, such as between the branchial plumes of a dorid nudibranch.
It not only gets protection from its giant host. The emperor shrimp will also benefit as it does not need to hunt for food – instead, as the host moves and eats, it churns up sand, and the food is practically handed to the shrimp!
Although the emperor shrimp is considered a commensal shrimp, there is evidence to suggest that they will eat parasites and fungus from their hosts, which actually means that they form a mutualistic relationship (where all parties involved benefit from the relationship) with their host, rather than a commensal relationship.
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This piece was prepared online by Panuruji Kenta, Publisher, SEVENSEAS Media