Gone fishin': decorator crabs use other species as fishing rods, study reveals

A researcher's diving holiday lead to a startling discovery of never-before-seen behaviour: crabs using hydrozoans as fishing hooks

Every night as the sun goes down, on the coral reefs of the Red Sea small, delicate and slightly fuzzy-looking crabs work their way through the maze of coral. They take up stations atop the corals' outermost structures, exposing themselves to the current in the plankton-rich waters. These are decorator crabs, of the genus Achaeus, known for their peculiar habit of covering themselves with an array of invertebrates, including delicate hydrozoans: multi-headed creatures with tiny tentacled polyps that feed on plankton.

In a recent paper published in the journal Marine Biodiversity, Dr Joan J Soto ingel, from the University of Valencia, suggests that the crabs are not only benefitting from the camouflage and defence the hydroids provide, but are also "fishing", using their covering of hydrozoan polyps as the hooks.