The relationship between these 'Shrimp Goby' and their 'Shrimp' reminds me of the expression 'which came first, the chicken or the egg?'
The Goby has pretty good eyesight and lives on sand. The trouble with living on sand is that there is nowhere to hide when something comes to eat you.
The Shrimp has pretty bad eyesight and lives on sand. The trouble with this is that you cannot see the predator that is about to eat you.
So these two very different creatures have formed a very clever relationship. The Shrimp is very good at digging and digs extensive tunnels under the sand. The tunnels, due to the nature of the shifting sands, are always collapsing and in constant need of repair. When excavating and repairing the tunnels, the shrimp have to push the debris out of their tunnel. At this point they are very vulnerable to predators.
The Goby, which cannot dig, acts as a lookout, with it good eyesight. It sits just outside the entrance to the tunnel and keeps a sharp eye out. When it sees anything approach, it wiggles it's body and shoots back into the tunnel.
The shrimp, if you look at the video, when it's out of the tunnel, always keeps one of it's antennae on the body of the goby. This way it can tell if there is danger nearby, as it can feel the goby twitch and then it too can rapidly disappear into the safety of it's tunnel.
It is rather hard to film these guys, as my camera has to be pretty close to the action, and usually the Shrimp Goby senses danger and goodbye goby and shrimp. By remaining very still for a long time and finding the idiot goby, I managed to finally get some good footage.
The shrimps are amazingly good at digging and moving small rocks around, while all the time keeping one antenna on the goby.
And so back to my first sentence...how did this relationship start. Nature is a wonderful thing indeed. This relationship is called Mutualism, which is where different species both benefit from their relationship with each other.