Brian Parata cleaning NIWA Ikatere. (Photo: NIWA Dave Allen)
Vessel noise increases fouling: study
Tuesday, January 31, 2012, 15:20 (GMT + 9)
Scientists at the National Institute of Water and Atmospheric Research (NIWA) and Auckland University have discovered that the underwater sounds made by vessels greatly exacerbate the fouling of those vessels by marine life.
Marine fouling caused by the growth of marine creatures on hulls represents a tremendous expense due to the amplified drag on ships' hulls and attempts to prevent the transport of organisms all around the world. Millions of dollars are spent yearly to try to control fouling.
It is known that sound triggers the larvae of many coastal organisms, such as mussels, to settle more rapidly. In some areas, underwater sound from human activities in the marine environment is increasing by two to four times each decade, largely as a result of increased international vessel traffic.
Scientists conducted laboratory experiments to find out whether the sounds caused by ships and their equipment are attracting fouling organisms.
"We recorded the noise generated by a range of different vessels while they were in port in Wellington, including NIWA's Tangaroa and commercial vessels such as log transport ships, container ships and cruise ships", said NIWA biosecurity scientist Dr Serena Wilkens.
|Dr Serena Wilkens (Photo: NIWA Dave Allen)
The scientists put an underwater microphone into the water next to the ships' hulls while they were berthed in port and recorded the sound intensity and frequency from the ships' generators, which still run when ships are in port and produce considerable underwater noise.
At the Leigh Marine Laboratory, the ship sounds were played to mussel larvae over several hours at two different intensities using submersible speakers while another group of larvae were not exposed to noise. The larvae were at a pre-settlement stage, which means that they were swimming in the water seeking a place to settle and attach.
"We found that the mussel larvae exposed to the high intensity vessel sound settled and metamorphosed a lot quicker than the ones in the silent treatment; significantly quicker", told Wilkens.
She said the scientists concluded that the vessel noise caused a higher percentage of mussel larvae to settle -- and to do so within just a few hours, which is within the timeframe that the larvae would be exposed to the noise from a generator in a vessel in port.
The NIWA and Auckland University scientists wish to suggest ways of reducing the underwater noise produced by ships, such as dampening or eliminating it or switching to a shore-based electrical supply while berthed.
The results of their research were published in Biofouling, a world-leading journal for researchers working to understand and prevent fouling.
This research was funded by NIWA, the University of Auckland and the Glenn Family Foundation.
By Natalia Real