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Need a Lift? Seahorses Ride Seaweed to Cross the Ocean, Study Finds

Seahorses aren’t great swimmers. But it turns out they’re pretty good hitchhikers.

A new study found that seahorses, as well as pipefishes, disperse through the Gulf of Mexico and along the Atlantic Coast by hitching rides on rafts of seaweed that follow ocean currents. The findings could have implications for seagrass habitat conservation.

The research was published in Proceedings of the Royal Society B. Authors on the paper include Professor Michael J. Hickerson (The City College of New York, The Graduate Center), former Hickerson lab postdoctoral researchers Laura Bertola and John Robinson, and Ph.D. alumni J.T. Boehm, Alexander Xue, and Isaac Overcast.

Seahorses and pipefishes belong to the Syngnathidae family. Because both are poor swimmers, scientists had wondered how they were transported over large distances. A common guess was that they were transported via large rafts of Sargassum seaweed that are carried along by Gulf Stream currents. The new study confirmed this.

The researchers sampled genetic material from two seahorse species and three pipefish species at 15 sites along the Gulf and Atlantic coasts. By comparing genetic traits from the different areas, they could tell that the fish had been migrating in the same direction as the ocean currents.

If the fish were indeed taking rides on rafts, two of the species would be doing so less than the other three, the scientists hypothesized, because they live closer to shore and associate less with Sargassum. Their results agreed—those two species showed less gene flow along the coasts than the other three.

Both seahorses and pipefishes are considered “indicator” species, meaning scientists can study them to find out how the larger ecosystem is doing. This makes them useful for conservation.

“I believe that we can only effectively conserve biodiversity if we know how species are distributed and what is driving their distribution,” Bertola said. “Genomics is opening up new possibilities to achieve that, because we can get a much better insight into connectivity between populations and a possible link to the environment they live in.”

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Michael J. Hickerson (Associate Professor, Biology) | Profile 1 | Profile 2