Fish Larvae Sniff Their Way Back Home: A Study

Fish larvae that have wandered away from the reef are able to navigate their way back via smell, a new study found, solving a mystery that has long puzzled scientists.

Previously, the team of researchers behind the new study established that reef fish larvae could discriminate between the odors of different nearby reefs; however, the past experiment, published in the Proceedings from the National Academy of Science, was performed under controlled conditions in a shore-based laboratory.

In the new study, which appears the journal PLOS-ONE, the team examined the larvae in a natural open ocean setting using an outflow plume from One Tree Island located in the Great Barrier Reef.

"In this collaborative study we expanded our work to demonstrate that the odor responses can also be detected under the field conditions," Jelle Atema, a professor of biology at Boston University, explained in a statement. "This establishes for the first time that reef fish larvae discriminate odor in situ."

This was done by observing two deployments to the north and south of One Tree Island, wherein single larvae were examined in the central chamber of an o-Disc, a contraption designed to recreate a behavioral arena transparent to light, sound and small scale turbulence. Using it, the scientists were able to track larval movement and orientation using odor cues from the environment.

In doing so, the species from the two reef-fish families reacted differently to the olfactory stimulus, with cardinalfish speeding up in response to odors and adopting a seemingly random swimming pattern while damselfish tended to slow down and orient themselves along the shoreline and westward.

"Ocean currents do not appear to influence the orientation of fish larvae," Claire Paris, the study's lead and a professor at the University of Miami, said. "They do not provide a frame of reference since larvae are transported within. Instead, we find that fish larvae navigate by detecting turbulent odor signals transported kilometers away from the reef. Subsequently they switch to a directional cue, perhaps magnetic or acoustic, which allows them to find the reef."

Knowing this, Paris argues, holds significant implications in regards to human activity and larvae's navigational success.

"If these larvae cannot get their 'wake up' cues to orient back toward the reef they may stay out at sea and become easy prey before finding home," Paris said.