Barnacles' sticky secret revealed

By Jody Bourton
Earth News reporter

Inside out, a cross section of a barnacle

Barnacles are able to attach themselves to almost anything.

They are found clinging to the hulls of ships, the sides of rock pools and even to the skin of whales.

Just how they stick so steadfastly whilst underwater has remained a biochemical puzzle for scientists for many years.

Now researchers have solved this mystery, showing that barnacle glue binds together exactly the same way as human blood does when it clots.

Barnacles are crustaceans that live in shallow ocean environments.

We've found homologous enzymes in barnacles and humans Dr Gary Dickinson Duke University, US

As larvae they affix to hard substrates, then remain stationary for the rest of their lives.

To attach themselves to a surface, the barnacles secrete an adhesive substance.

Scientist knew the chemical properties of this glue, but not how these chemicals interact to create a sticky effect.

Now researchers reveal all in The Journal of Experimental Biology.

Sticking point

Actually obtaining some barnacle glue proved an initial hurdle.

"No one really knew how to work with barnacle glue before this study," says Dr Gary Dickinson, a member of the research team from Duke University's Marine Laboratory in Durham, North Carolina, US.

"Most people try to cut it off the bottom of a barnacle and then dissolve it, but we knew this does not work well, and this approach has limited potential," he explains.

Sticking around

So Dr Dickinson and his colleagues learnt how to gently remove glue from the barnacles (Amphibalanus amphitrite) as they secreted it.

They were then able to deconstruct the glue to find out exactly how it works.

The team initially compared the glue to another substance which clots in solution; red blood cells.

They expected the mechanism by which glue particles bind, and red blood cells bind, to be different.

However, they found they are remarkably similar.

In blood, a number of enzymes work to create long protein fibres that bind red blood cells together into a clot and create a scab.

Using techniques including atomic force microscopy and mass spectrometry, the team found that very similar enzymes, known as trypsin-like serine proteases, are at work in barnacle glue.

One of these glue enzymes is remarkably like Factor XIII, an essential blood clotting agent in human blood.

The enzymes are highly conserved because they are very effective at what they do Dr Gary Dickinson Duke University, US

"We've found homologous enzymes in barnacles and humans, which serve the same function of clotting proteins underwater, despite roughly a billion years of evolutionary separation," says Dr Dickinson.

However, this surprising result does make evolutionary sense, says team member Professor Dan Rittschof, also from Duke University's Marine Laboratory.

"Virtually no biochemical pathway is brand new. Everything is related and really important pathways are used over and over," he explains.

"Really key parts of those pathways can't change because if they do, the pathway fails and the animal dies."

Glue potential

Dr Dickinson believes other organisms might also use this glue.

"The enzymes are highly conserved because they are very effective at what they do."

"There are bound to be a number of other organisms that use the same enzymes for the same purpose," he says.

His team hopes that further research might lead to a solution to the problem of marine fouling, where barnacles stick to boat hulls creating drag.

Many anti-fouling compounds used to paint the undersides of boats are toxic, so Dr Dickinson's team hopes to find a more environmentally-friendly solution.