Biosecurity news

A Cawthron scientist inspects a sea chest on a merchant ship
12 July 2013

Could it be this simple? Scientists use heated sea water to control biofouling

In collaboration with NIWA, Cawthron scientists recently completed a series of laboratory and field-based trials to test the efficacy of heated seawater in eliminating biofouling in sea chest habitats.

“The results of our preliminary work are very promising” says Dr Grant Hopkins of the Cawthron Institute. “Temperatures in the range of 37.5 to 42.5°C for less than 1 hour are effective in killing the majority of organisms you’d expect to find in a vessel sea chest.”

A complex problem

A diverse range of marine organisms grow on vessels and other artificial structures deployed in the marine environment such as wharf piles, marina pontoons and pipelines.

Often termed ‘biological fouling’ or ‘biofouling’, these assemblages can include both sessile and mobile organisms with varying morphologies.

Even when a vessel is painted with a biocidal coating and maintained to specifications, biofouling can still establish on parts of the vessel where paint is not applied or is in poor condition, such as gratings, propeller shafts and sea chests.

Vessel biofouling can increase running costs as a result of the increased drag through the water and the requirement for more regular maintenance.

It can also pose a biosecurity risk as organisms attached to the hull of a vessel can be transported beyond their natural range.

Working with industry

Although further validation trials in vessels would be ideal, Dr Hopkins says it is now time to get vessel engineers on board with the project to design systems that ensure the entire sea chest is heated to the required temperature.

“We built a replica sea chest and placed a range of fouling taxa and an array of temperature probes to see what would happen when we heated the water,” he says. “We were surprised at how difficult it was to get the entire sea chest heated up to the required temperature.”

Pacifica's 100-metre long container vessel, The Spirit of Resolution, already pumps heated seawater through the sea chests, and Cawthron scientists have undertaken limited trials on the efficacy of the existing system.

“When heated seawater, generated by the engines, is discharged through the chests, maximum temperatures of around 25-30°C for about 20 to 40 minutes are readily achieved,” Dr Hopkins says. “This is promising, but higher temperatures are needed to be effective on the types of organisms found in sea chests.”

Encouraging signs

Dr Hopkins is encouraged by the results obtained to date.

“This research, along with NIWA’s work investigating the role sound plays in vessel biofouling indicates that significant gains in biosecurity management may be possible through some rather straight-forward changes in vessel design,” he says. “The challenge now is for the shipping industry to use research undertaken in the programme to benefit their operations.”

Image top right: A Cawthron scientist inspects a sea chest on a merchant ship.

For further information contact Grant Hopkins.