Tiny shrimp rely on “odour bouquet” to find their way home

Marine biologists have shown that a migratory shrimp species relies on smell – chemical signatures – to pinpoint their home cave. Some of the chemicals they respond to appear to be sensitive to climate change.

Animals that can navigate back to an original location, such as a breeding spot or nesting site, are said to have homing ability. Homing animals appear across the evolutionary tree, including salmon, bees, pigeons, rats and sea turtles.

Homing animals are known or suspected to use a wide variety of cues such as physical landmarks, Earth’s magnetic field and light from the night sky.

In a new study published in Frontiers in Marine Science, French scientists demonstrate that tiny shrimp called mysids use smell to return home after nightly foraging migrations.

“Here we show for the first time that mysids can tell the water-borne odour bouquet – its so-called chemical seascape – characteristic of their home cave,” says Thierry Pérez, CNRS research director at the marine research station of Endoume near Marseille in France, and the lead author of the study.

To conduct their study, Pérez and colleagues captured hundreds of the cave-dwelling mysid species Hemimysis margalefi from two different caves in the Mediterranean Sea off southern France.

In a behavioural experiment, the scientists presented individual shrimp with a choice between two tanks, each filled with seawater from one of the two home caves, a nearby cave or control seawater. The time each shrimp spent in the tube connected to one of these tanks was used a proxy for their preference.

The results showed that H. margelefi strongly preferred water from their own cave, with individuals spending three to 16 times longer in the water from their home cave.

The scientists also used ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry to identify differences in odour-producing metabolites between the caves. These included natural peptides, fatty acids, steroids and alkaloids, as well as anthropogenic pollutants. 

Pérez and colleagues hypothesise that sedentary or “sessile” marine organisms like sponges, which are abundant in these caves, produce many of the specialised metabolites that give each cave its signature odour bouquet.

“Our results suggest that any change in water quality or sessile fauna inside caves can alter their chemical seascape, with a likely negative impact on the functioning of the whole ecosystem,” says Pérez.

Mysid shrimp are important zooplankton species that provide food for other marine organisms.

“We are currently following up on our results by trying to correlate the chemical seascapes from different caves with the biodiversity of sessile organisms living in them,” says Pérez.