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Cave-dwelling shrimp (Hemimysis margalefi) use chemical smells of water to navigate home

Cave-dwelling shrimp (Hemimysis margalefi) use chemical smells of water to navigate home

NEWS - Cave-dwelling shrimp (Hemimysis margalefi) find their way home in the vast ocean using the special scent of their cave. Tiny mysid shrimps use scent to track their way home thanks to local differences in the ‘chemical seascape’

Animals have the ability to navigate to their home locations, breeding grounds and feeding areas. Salmon, pigeons, bees, frogs, mice, sea turtles rely on landmarks such as the Earth’s magnetic field, patterns of polarised light in the sky and so on to find their way back.

Cave-dwelling mysid shrimps, also known as possum shrimps because the females have a pouch to carry their larvae, also use chemical cues to navigate underwater caves in the same way that coral larvae and reef-dwelling fish distinguish between healthy and disturbed coral reefs.

“For the first time we show that mysids can distinguish between waterborne scents that characterize their caves, in addition to the scents of nearby caves. This distinctive seascape helps them find their caves again when they return from their nightly migrations,” says Thierry Pérez of Aix Marseille Université.

H. margalefi lives in sea caves in the northwestern Mediterranean forming dense swarms with millions of individuals per cave. At dusk, they move hundreds of meters into open water to feed on algae, detritus and other zooplankton. At dawn, they return to the same caves to seek shelter from predators.

The researchers took seawater samples from three caves in the Calanques National Park off the coast of southern France. The caves are between 11 and 24 meters underwater and are between 8 and 20 kilometers apart. They also collected individuals of another mysid species that does not live in caves but lives in shallow water.

The shrimp were placed in a Y-shaped channel. Each arm was connected to a 10-liter tank filled with seawater from one of the caves. This water flows out of the tank into the channel at a rate of 50 milliliters per minute carrying away all water-soluble metabolites.

The researchers tested 286 individuals of which 230 were H. margalefi and 56 were Leptomysis. Experiments were conducted in the morning and afternoon to test the effect of time on shrimp preferences, but there was no effect.

Individuals from Jarre cave spent 16 times longer in the group with Jarre water than in the group with 3PP water, while individuals from Fauconnière cave spent three times longer in the group with Fauconnière cave water than in the group with 3PP water.

Individuals from Jarre cave did not prefer Fauconnière water to 3PP water, while individuals from Fauconnière cave did not prefer Jarre water to 3PP water. Similarly, non-cave Leptomysis never preferred one type of water to the other.

The seascape was composed mainly of natural peptides, fatty acids, steroids, alkaloids and anthropogenic pollutants. The chemical signature of Jarre water was very different from that of Fauconnière water, while the chemical signature of 3PP water was intermediate between the two. Sessile organisms such as sponges that are abundant in caves and produce many specialized metabolites are major contributors to the local seascape.

“We know that food availability in marine cave ecosystems is highly dependent on the daily migration of zooplankton such as mycids. We show that any change in water quality or sessile fauna in the cave can change its chemistry with possible negative impacts on the functioning of the entire ecosystem,” Pérez said.

“It is worrying that mass mortality of sponges and corals is becoming more frequent due to climate change. We are following up by testing the biodiversity of sessile organisms living in them, focusing on the role of metabolites from sponges and corals,” Pérez said.

Original research

Derrien Marie, Santonja Mathieu, Greff Stéphane, Figueres Soizic, Simmler Charlotte, Chevaldonné Pierre, Pérez Thierry (2024). Circadian migrations of cave-dwelling crustaceans guided by their home chemical seascape. Frontiers in Marine Science, Volume 11, DOI:10.3389/fmars.2024.1448616

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