Seahorse ‘hitchhikes’ Atlantic

Navigating the world’s oceans can be a difficult task for anyone.

For a tiny seahorse with only small fins and a tail for locomotion it seems an impossible task.

However, a seahorse that lives on the western coast of the Atlantic has been found in the Azores almost 5000km away from its possible home.

Researchers suggest the seahorse may have completed the epic journey using its prehensile tail to hitch a ride on a raft of floating sea grass.

An international team of researchers from the UK and the Azores publish their discovery in the Journal of Fish Biology.

Lost at sea

The seahorse was found by a fisherman on the isolated Azores archipelago in the eastern Atlantic.

Two species of seahorse Hippocampus guttulatus and Hippocampus hippocampus are native to Europe and the Azores, an autonomous region of Portugal.

The researchers compared the morphology and DNA of the seahorse with the two native species and found it was a lined seahorse Hippocampus erectus usually found along the Atlantic coast and Caribbean sea coasts of North, Central and South America.

“We were surprised to identify the unknown seahorse as H. erectus, as this species is found thousands of kilometres away,” says molecular ecologist Dr Paul Shaw from the Royal Holloway, University of London, UK.

“The specimen DNA sequence was almost identical to DNA sequences from individuals of H. erectus collected in the US, and very different to DNA sequences of H. guttulatus and H. hippocampus which are native to this region,” Dr Shaw explains.

The researchers say that this is the first record of the species in the eastern Atlantic.

Seahorses are cryptic animals and blend into their habitat living among seaweed in shallow water along coastlines.

So exactly how it arrived on the other side of the Atlantic in the Azores was a puzzle for the researchers.

Life raft

They suggest the seahorse may have been released by someone who had kept it in an aquarium.

Another possibility is that the fish may have been transported to the Azores in the ballast water of a ship.

However, the most likely explanation, the researchers believe, is that the seahorse hitched a ride across the ocean on a floating raft.

“The seahorse attaches itself to some floating material such as seaweed or other vegetation, then this ‘raft’ is carried by prevailing Gulf Stream currents away from the American coast and across the Atlantic to the Azores,” Dr Shaw says.

Dr Lucy Woodall, also from Royal Holloway, University of London, led the study.

She belongs to the international research group Project Seahorse and explains how genetic studies suggest that other seahorse species may have undergone long range dispersal.

Seahorses have also been observed in the middle of the ocean holding on to floating seagrass with their prehensile tail, hinting that this transient seahorse may have done the same.

“In the open ocean, fish are found under these type of ‘rafts’, as they provide protection and harbour small prey items, therefore [it is not unusual] for seahorses to use these structures,” Dr Woodall says.

Dr Woodall believes that although the seahorses are hard to find in the wild, due to their excellent camouflage, a lack of sightings in the Azores and Europe suggests it is unlikely that it occurs in greater numbers on the eastern side of the Atlantic.

“It’s interesting and points that further research is required, but it cannot lead to the conclusion that there are more H. erectus in the Eastern Atlantic,” she concludes.

“We just don’t know.”