How do coral reef critters find home?

The life cycles for many coral reef animals are a bit tricky. Coral reefs are huge feeding bodies with billions of mouths looking for food. Much of that food is provided by the inhabitants of the reef itself – and the smaller the inhabitant the more vulnerable they are to becoming food. This makes the whole business of being born a dicey affair.

Many coral reef animals reproduce by gamete dispersal, so the sea serves as their “womb.”  In order to stay out of harm’s way the larval animals will float or propel away from the reef and live in a pelagic (open water) phase of their life until they become large enough to recruit back to the “mother reef.” But how do they find home?

 Photo:  Iliana Baums.  Penn State University

Photo: Iliana Baums. Penn State University

About a decade ago researchers found that larval stage reef animals imprint on the sound of their originating reef, allowing them to find home when they are large enough to recruit back to the reef. This understanding brought up a concern that human-generated noise from motor boats (or jet skis) might somehow disrupt this imprinting and way-finding adaptation, either by masking important sound cues, or by creating a false imprint signal for the larval animals.

Just recently one aspect this disruption was found to be true – that larval fish swam away from reef sounds mixed with boat noise. Using ‘orientation tubes’ fitted with speakers Steve Simpson and his research crew found that the larval fish were evenly distributed with playback of ambient sounds, swam toward reef sounds, and away from the boat noise/reef sounds mix.

This understanding adds yet another quandary in ocean noise management. In a reef environment where sound is a dominant orienting sense we humans need to find ways of being better neighbors.