Colonial forces

A shrimp of the genus Synalpheus, found in a colony in a sponge.


23 May 2010
Discovering a colony of social snapping shrimps of the genus Synalpheus has been a highlight of the CReefs Ningaloo expedition for Dr Arthur Anker of the Florida Museum of Natural History.
"This shrimp, a species of Synalpheus, is presently considered the only social marine invertebrate," Dr Anker says.
"Social colonies have been found in the Caribbean, but the colony we found on Ningaloo Reef is the first clear proof of their existence in the Indo-West Pacific," he says.
Dr Anker found the shrimp colony in a sponge. The colony comprised more than 50 individuals, all descendants of the same female, the "queen".
A shrimp of the genus Synalpheus, found in a colony in a sponge.
"Only the queen has embryos; it is the only reproducing female in the colony," Dr Anker says.
"There must be one or several males to fertilise the queen, but we cannot distinguish the king from the other colony members without conducting paternity testing, which is possible but very expensive and time-consuming," he says.
"We also don't know yet how the queen is able to suppress the reproduction of other colony members," he says.
Dr Anker theorises that living in a colony might allow the shrimp to better defend their home.
"Sponges are in high demand as habitat for animals on reefs. Social shrimp, by forming these large groups, can take over the entire sponge. They probably defend the sponge together, so if a worm or another shrimp is trying to get in, the shrimp may combine forces, snap at it aggressively, and chase it out," says Dr Anker.
Dr Anker's main research focus is on the snapping shrimps of the family Alpheidae. One of the most conspicuous feature of snapping shrimps is an oversized claw that the shrimp snap – hence the name – for self-defence, stunning prey, and possibly also for communication.
"Most alpheid shrimps live in pairs, but like this species, rarely in colonies. Normally they are quite aggressive and they would immediately start snapping at each other, but these Synalpheus shrimps are living together in a similar system to termite colonies," Dr Anker explains.
Shrimps are among the most abundant and diverse creatures found on coral reefs. The genus Alpheus, for instance, has approximately 300 known species, but Dr Anker estimates there may be as many as 800-1000 species worldwide.
Dr Anker is the only researcher in the world currently specialising in alpheid shrimps. His participation in the CReefs expedition to Lizard Island in February 2009 resulted in the identification of at least three new species in this family.