WELLINGTON, Jan. 30 — New Zealand scientists said on Monday they have found a possible answer to a multi-million-dollar problem for shipping companies around the world.
Simply switching off a vessel's generator when it is berthed and using a shore-based electricity supply might significantly reduce the problem of marine fouling, caused by marine organisms settling on ships' hulls and propellers, they say.
Scientists at the National Institute of Water and Atmospheric Research (NIWA) and Auckland University found the noise of generators acted like a magnet for fouling organisms, such as mussels, said a statement from NIWA Monday.
The findings could save millions of dollars spent each year on attempts to control fouling on commercial vessels and reinforce biosecurity by preventing organisms being carried around the world outside their native habitats, it said.
The larvae of many coastal organisms, such as fish and crab larvae, were attracted to the underwater sound of waves breaking on coastal reefs and noises produced by other reef-dwelling organisms during feeding.
Sound traveled long distances through water, without being affected by currents, wave action or the clarity of the water so it provided a reliable settlement cue.
However, in some areas, underwater sound from human activities in the marine environment was doubling or quadrupling each decade, largely as a result of rising international vessel traffic.
"We recorded the noise generated by a range of different vessels while they were in port in Wellington, including NIWA's ( research vessel) Tangaroa and commercial vessels such as log transport ships, container ships and cruise ships," NIWA biosecurity scientist Dr Serena Wilkens said in a statement.
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 their generators, which were still running.
In a controlled laboratory environment, the ship sounds were played over several hours to mussel larvae at two different intensities using submersible speakers, while another group of larvae was kept in silent tanks.
"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," said Wilkens.
Wilkens said scientists could conclude that the vessel noise caused a higher percentage of mussel larvae to settle, and to settle a lot quicker.
The scientists were hoping to suggest ways of reducing the underwater noise from ships, such as dampening or eliminating sound or switching to shore-based electrical supply while berthed, said the statement. (PNA/Xinhua) DCT/utb