Gobies and shrimps work together for each of their survival. There are more than hundred species of goby that share a burrow with a shrimp. The two species can even communicate when the shrimp touches the dorsal, caudal or anal fins of the goby with one of its antennae. But how do shrimps and gobies find each other in the first place, for them to establish their alliance?
The gobies and the shrimps find each other by a combination of sight and smell. The shrimp only lets new goby applicants of certain species into its burrow, and it smells the ones are the goby equivalent of Mr Right. The goby picks shrimp by inspecting the patterns on their carapace, and it also chooses only burrow entrances which fits its size.
There is no specific one-on-one pairing between one species of shrimp and one species of gobies. Rather, a complex set of rules governs which species of shrimp wants to work with which type of goby and vice-versa. Typically, one species of goby shares burrow with several species of shrimps.
There is something about shrimps that makes them want to cooperate with others. At the same time, gobies generally have the tendency to hide into dark crevices or burrows, so they would naturally be drawn to a burrow-digging partner. Hence, the alpheid shrimp-goby partnership is such an obvious winner that it got started several times independently, and flourished in every case.
The symbiosis between gobies and shrimp has been successful not only when looking at the number of goby species that live with a shrimp, but also when taking into consideration how frequently one can find such pairs underwater.
If you snorkel above a seagrass meadow or a sandy underwater area, you can observe several of such goby-shrimp pairs per square metre. These relatively featureless places would otherwise be completely off-limits for small defenceless fish and crustaceans with poor visions — they would end up as lunch for the many predatory fishes of the tropics. This success if not due to any spiny fin or poisonous skin that gave the gobies a decisive advantage in the struggle for survival, but their partnership with the shrimp.
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