In what appears to be a mysterious petroglyph, a branching groove in a living Porites coral colony is occupied by a pair of snapping shrimp, Alpheus deuteropus. Although the shrimp live in burrows within the grooves and are never seen, they crawl up and down the channels feeding on algae growing between and around the tiny hydroids that line the grooves. It is thought the shrimp may create the grooves using chemicals that kill the coral. (If you're not sure what a petroglyph is, here is one from Puako on the island of Hawaii.)
20 July 2014