and the winner is…the goby!
by Professor Ellen Thayer
utterance can be confirmed very clearly in the aquarium: newly introduced symbiotic gobies, compromised
by stress, which fail to perform this sign language, this
rhythmic tail-beating, are immediately attacked, seized,
and, if they aren’t strong enough to struggle free in short
order, disappear into the dark passage system of the pistol shrimp, never to be seen again.
How does tHe symbiosis function?
And this, of course, now raises some fundamental questions. How, on what basis, does this symbiosis function?
Let us take another look at the currently accepted
wisdom: the shrimp is (almost) blind, and hence has
to rely on the sharp-sightedness of its goby. The latter
signals (via tail-beating and antenna contact) either
“No enemy in sight” or “Watch out, enemy coming”,
and then the shrimp knows whether to feed in the open
or not, as the case may be. In return the shrimp digs
away from morning to night, keeping the entrance to the
caves clear or creating new ones. (See The Shrimpgobies of
Raja Ampat by Scott Michael in this issue, page 56.)
But the fact is that the shrimp’s being blind isn’t relevant to any need to come out of the cave to feed (on the
contrary, it finds the bulk of its food in the subterranean
passageway system), but it does need to clear excavated
material out of the passages. And when doing so it is
clearly advantageous to be warned of enemies by its goby.
On the basis of aquarium observations pistol shrimps
with no goby are more circumspect when disposing of
building “spoil” and invest less time in excavation work
outside the cave entrance. From the goby’s point of view
it is clear that the availability of a cave system is advantageous, although any partner goby is perfectly capable
of digging its own hole. So why does it place such value
on the pistol shrimp, which represents a threat to it and
which it must constantly appease via beats of the tail in
order to avoid being eaten?
Perhaps the advantage for the goby lies on a completely different level. And here I return to three observations I have made in different aquaria, all involving
symbiotic-goby and pistol-shrimp partnerships. I am,
you see, fond not only of my symbiotic pairs but also
Cryptocentrus cinctus pair with “bodyguard”: Alpheus bellulus.