Seahorse heads have a 'no wake zone' that's made for catching prey

November 26, 2013
The dwarf seahorse, Hippocampus zosterae, has a head perfectly shaped to sneak up on fast moving copepods. Credit: Brad Gemmell

Seahorses are slow, docile creatures, but their heads are perfectly shaped to sneak up and quickly snatch prey, according to marine scientists from The University of Texas at Austin.

"A seahorse is one the slowest swimming fish that we know of, but it's able to capture prey that swim at incredible speeds for their size," said Brad Gemmell, research associate at the University of Texas Marine Science Institute, which is part of the College of Natural Sciences.

The prey, in this case, are . Copepods are extremely small crustaceans that are a critical component of the . They are a favored meal of seahorses, pipefish and sea dragons, all of which are uniquely shaped fish in the syngnathid family.

Copepods escape predators when they detect waves produced in advance of an attack, and they can jolt away at speeds of more than 500 body lengths per second. That equates to a 6-foot person swimming under water at 2,000 mph.

"Seahorses have the capability to overcome the sensory abilities of one of the most talented escape artists in the aquatic world—copepods," said Gemmell. "People often don't think of seahorses as amazing predators, but they really are."

In calm conditions, seahorses are the best at capturing prey of any fish tested. They catch their intended prey 90 percent of the time. "That's extremely high," said Gemmell, "and we wanted to know why."

This video is not supported by your browser at this time.
Seahorses have heads perfectly shaped to sneak up on copepods without alerting them, because the area just above and forward of their nostrils produces no fluid disturbance. This video shows a seahorse sneaking up and capturing a copepod. Credit: Brad Gemmell, Ed Buskey and Jian Sheng.

For their study, Gemmell and his colleague Ed Buskey, professor of , turned to the dwarf seahorse, Hippocampus zosterae, which is native to the Bahamas and the U.S. To observe the seahorses and the copepods in action, they used high-speed digital 3-D holography techniques developed by mechanical engineer Jian Sheng at Texas Tech University. The technique uses a microscope outfitted with a laser and a high-speed digital camera to catch the rapid movements of microscopic animals moving in and out of focus in a 3-D volume of liquid.

The holography technique revealed that the seahorse's head is shaped to minimize the disturbance of water in front of its mouth before it strikes. Just above and in front of the seahorse's nostrils is a kind of "no wake zone," and the seahorse angles its head precisely in relation to its prey so that no fluid disturbance reaches it.

Other small fish with blunter heads, such as the three-spine stickleback, have no such advantage.

Gemmell said that the unique head shape of seahorses and their kin likely evolved partly in response to pressures to catch their prey. Individuals that could get very close to prey without generating an escape response would be more successful in the long term.

"It's like an arms race between predator and prey, and the seahorse has developed a good method for getting close enough so that their striking distance is very short," he said.

Seahorses feed by a method known as pivot feeding. They rapidly rotate their heads upward and draw the in with suction. The suction only works at short distances; the effective strike range for seahorses is about 1 millimeter. And a strike happens in less than 1 millisecond. Copepods can respond to predator movements in 2 to 3 milliseconds—faster than almost anything known, but not fast enough to escape the strike of the seahorse.

Once a copepod is within range of a , which is effectively cloaked by its head shape, the copepod has no chance.

Gemmell said that being able to unravel these interactions between small fish and tiny copepods is important because of the role that copepods play in larger ecosystem food webs. They are a major source of energy and anchor of the marine food web, and what affects copepods eventually affects humans, which are sitting near the top of the web, eating the larger fish that also depend on copepods.

Gemmell, Buskey and Sheng published their research this week in Nature Communications.

Explore further: How the seahorse might have got its shape

Related Stories

How the seahorse might have got its shape

January 27, 2011

( -- The shape of the seahorse has long baffled marine scientists, but new research suggests the seahorse’s unique shape may have evolved to allow it to catch its food when it was further away.

Research puts seahorse flash photography safely in the frame

November 12, 2013

( —Do relatively non-invasive research methods like flash photography harm or change the behaviour of the very creature being investigated? It's an ethical dilemma frequently faced by environmental scientists, ...

Open wide: Zebrafish fool fast food

November 14, 2013

Research published in the Royal Society Journal, Interface, has demonstrated that predatory fish sneak up on lightning-fast prey by disguising water disturbances as they approach.

Recommended for you

Scientists overcome key CRISPR-Cas9 genome editing hurdle

December 1, 2015

Researchers at the Broad Institute of MIT and Harvard and the McGovern Institute for Brain Research at MIT have engineered changes to the revolutionary CRISPR-Cas9 genome editing system that significantly cut down on "off-target" ...

Study finds 'rudimentary' empathy in macaques

December 1, 2015

(—A pair of researchers with Centre National de la Recherche Scientifique and Université Lyon, in France has conducted a study that has shown that macaques have at least some degree of empathy towards their fellow ...

Which came first—the sponge or the comb jelly?

December 1, 2015

Bristol study reaffirms classical view of early animal evolution. Whether sponges or comb jellies (also known as sea gooseberries) represent the oldest extant animal phylum is of crucial importance to our understanding of ...

Trap-jaw ants exhibit previously unseen jumping behavior

December 1, 2015

A species of trap-jaw ant has been found to exhibit a previously unseen jumping behavior, using its legs rather than its powerful jaws. The discovery makes this species, Odontomachus rixosus, the only species of ant that ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.