Smart, tough, and hungry, an octopus is near the top of the ocean’s predatory hierarchy. That makes it odd to see an octopus flee, repeatedly, from a few little damselfish. Watch an underwater mob, and learn what other animals these fish take on.
These damselfish are probably only defending their nest when they chase this octopus away to, presumably, mingle its tears with the salt water around it. That doesn’t make it any less impressive. Damselfish will go after most things that come too near their nest sites. They’ve been known to chase after and bite barracuda exactly this way—but octopuses are their most frequent target. Scientists have seen the behavior many times. Even youtube posters have managed to get multiple shots of it.
In fact, this behavior is so common that some octopuses have devised a way of getting around the constant bullying. While damselfish will go after an octopus without fear, they are afraid of sea snakes. The mimic octopus will run to a hole, hide most of itself, and leave a tentacle waving like a sea snake. That scares the damselfish off.
That’s a clever but cowardly display, coming from an animal that has been known to successfully kill sharks.