Ships' sticky situation dissolved

Victoria Vaughan, Straits Times 12 Dec 09;

THEY may each only be a few centimetres in size, but barnacles cost the shipping industry billions of dollars in cleaning and can increase fuel consumption by up to 25 per cent.

However, science may have brought a solution to this sticky situation a step closer. Building on previous studies, Dr Gary Dickinson, now based at the Tropical Marine Science Institute (TMSI) at the National University of Singapore, has uncovered the secrets of barnacle glue.

Although the basic properties of the glue were understood, the way it became sticky had remained a mystery until now. In the past, when scientists tried to analyse the glue, they would dissolve it in chemicals, but there would always be some solid element left over, making it hard to get the full picture.

'We tried to obtain the glue before it became sticky to find out how it works. After reading up about the anatomy of a barnacle and finding where the glue would come from naturally, we discovered if we put pressure on the barnacle in the right way we could collect the liquid glue,' said Dr Dickinson, who was aided by his PhD adviser, Professor Dan Rittschoff, when he carried out the work at Duke University in the United States.

As the enzymes, which speed up the mechanism of the liquid glue hardening, work best at body temperature, the glue collection was done in a cold room of between 0 deg C and 4 deg C. Even then, the glue, clear or pinkish orange in colour, can harden in five to 10 minutes.

To understand how barnacle glue sticks and hardens, Dr Dickinson compared the process to blood clotting.

'In evolution, important mechanisms are conserved. So we looked at mechanisms in animals that are important to survival, and clotting so they don't bleed to death is one such mechanism,' he said. 'We thought it would be a similar process to the barnacle, which needs to stick to things in order to survive and feed on plankton.'

He studied the components of the glue under an atomic force microscope and found it had a fibrous quality similar to that of a blood clot or scab - proving his original theory. This, along with the results from a variety of other analysis techniques, confirmed the ideas of Dr Dickinson and his colleagues.

Based on this discovery, he then tried using a common chemical to see if the glue could be prevented from hardening, and discovered the glue did not set.

This is bad news for the barnacle but could be good news for the shipping industry if this discovery could be translated into a paint for the bottom of ships. But Dr Dickinson said such a paint was still a few years away.

Ships travel faster and consume less fuel when their hulls are smooth and free from fouling caused by barnacles, algae or molluscs.

Lime arsenic and mercury were used in the early days of sailing ships. In the 1960s, anti-fouling paints using metallic compounds, in particular the organotin compound tributyltin (TBT), were developed and by the 1970s, most seagoing vessels had TBT painted on their hulls.

However, environmental studies found TBT to be harmful to surrounding marine life. Use of TBT was banned last year by the International Maritime Organisation, the United Nations agency concerned with the safety of shipping and the prevention of marine pollution.

At the moment, most ships use copper-based paints to repel or kill barnacles, or more expensive silicone paints which barnacles cannot attach to. Dr Dickinson's discovery could lead to another option for ship owners.

His research was funded by the United States Office of Naval Research. He is continuing his work at TMSI, looking at the initiation phase of glue hardening and also comparing the different species of barnacles.

Different species of barnacles can grow to different sizes, ranging from 1cm in diameter to between 10 and 13cm for the megabalanus, which is found here in Singapore and other tropical and semi-tropical regions, such as off the coast of Chile.