Although seemingly completely stationary, the beautiful corals that make up the heart of tropical reefs are actually able to swim as larvae (see movie above). Mature coral release eggs that are fertilized in the open ocean, and the resulting (kind of cute!) larvae spend their early days swimming in the currents. But baby corals can’t just settle down anywhere; they need the shallow water and habitat of the reef in order to thrive. So how do these free-swimming coral larvae find a reef? According to these scientists, the little guys use sound waves in the water to orient and swim towards the reef that they will eventually attach to and call home. To test their hypothesis, the researchers put coral larvae in special tanks and broadcast the sounds made by fish and crustaceans that live in reefs. Lo and behold, the baby corals oriented and swam towards the sound sources. Amazing!
“Free-swimming larvae of tropical corals go through a critical life-phase when they return from the open ocean to select a suitable settlement substrate. During the planktonic phase of their life cycle, the behaviours of small coral larvae. Here, we show that coral larvae respond to acoustic cues that may facilitate detection of habitat from large distances and from upcurrent of preferred settlement locations. Using in situ choice chambers, we found that settling coral larvae were attracted to reef sounds, produced mainly by fish and crustaceans, which we broadcast underwater using loudspeakers. Our discovery that coral larvae can detect and respond to sound is the first description of an auditory response in the invertebrate phylum Cnidaria, which includes jellyfish, anemones, and hydroids as well as corals. If, like settlement-stage reef fish and crustaceans, coral larvae use reef noise as a cue for orientation, the alleviation of noise pollution in the marine environment may gain further urgency.”