Coral, Full Moons and Hearing Hair Cells

Occasionally, The Audiology Condition posts on scientific studies that catch our interest, not because they necessarily have clinical application, but because they give insight into how hearing works and why hearing is important not only to humans but to other species as well.  

Today’s post looks at tiny organisms less than a millimeter in size.  Who knew they had ears? Who knew they could hear with them? Who knew their hearing could be tested?

Coral larvae are no bigger than fleas but recent research proves that they “hear” sound and use directional hearing in a sophisticated manner to increase their survival odds.  The proof was gathered by observing larvae floating aimless around in water tanks.  Aimless drifting behavior turned intentional, or at least non-random, when speakers in the tanks started playing reef sounds and the larvae headed for the speakers.

For several reasons, this is big news for marine biologists, but also for hearing scientists.  

  • First, it helps explain a crucial coral survival  strategy.  Every month when the full moon comes out, coral larvae use sound navigate to select and settle into the prime real estate of reefs.
  • Second, it establishes the hitherto unknown fact that these tiny creatures have “ear(s)” of some sort.  The form and function of these new ears remains a mystery, but scientists speculate that surface hair cells are disturbed by sound waves traveling through water.  This would be akin to us humans wearing our inner ears–with their 40,000 hair cells– out on our arms or finger tips.

Coral larvae live in a fragile survival system with fragile ears.  It wouldn’t take much noise to confuse the larvae and keep them from landing on a reef.  The scientists hypothesize this may be happening:

 “small boats, shipping, drilling, pile driving and seismic testing” are masking the reef sounds so that the larvae can’t find a safe home, thus providing an explanation for coral’s “well-charted decline in recent decades.”


ref:  Coral Larvae Move toward Reef Sounds

photo courtesy of Darwinism in Ruins