Invasive Species "Stowaways" May
Lose Rides on Ships
A new method to
reduce rust and corrosion in the ballast tanks of ocean
vessels may also be key to preventing the spread of foreign
aquatic species that stow away in ballast water.
Global shipping moves about 80 percent of the worlds'
commodities and is an essential part of world trade. But
when ships stop at ports around the globe, they deliver
not only their cargo but also a menagerie of aquatic hitchhikers
that lurk in the ballast tanksenclosures in ship
hulls that are filled with water to counterbalance a cargo
Every day thousands of ships suck up thousands of gallons
of water in one port and later release it in anothersometimes
thousands of miles away. The result: Hundreds of non-indigenous
species are introduced to different habitats each day.
In many cases the introduction of these "alien species"
wreaks environmental havoc, which collectively has caused
hundreds of millions of dollars in damage.
In 1986, for example, a ship that emptied ballast water
from the Black Sea into Lake Erie released a tiny stowaway,
the zebra musselnow the poster child of invasive
species. The dime-size mussel has reproduced uncontrollably,
spreading to the Hudson and Mississippi Rivers and even
the Gulf of Mexico, forming thick carpets of mussels that
clog pipes and waterways.
Solutions to the foreign-species transfer problem have
included using various filtration systems, heat treatments,
and biocides for the ballast water. Most of these approaches
have been dismissed as too expensive to install or because
biocides could be harmful to the environment.
Now, engineers at Sumitomo Heavy Industries in Japan
have developed a solution that should simultaneously benefit
the environment and please the shipping industry: remove
the oxygen from the ballast water.
"Simple and Elegant Solution"
The system developed by Sumitomo's engineers pumps nitrogen
gas through the ballast tanks to purge the seawater of
Reducing oxygen in ballast water to a low level can
kill as much as 80 percent of the organisms in the water,
according to the researchers. At the same time, a low
oxygen level reduces the amount of rusting.
"It's a simple and elegant solution," said marine ecologist
Mario Tamburri of the Monterey Bay Aquarium Research Institute
in Moss Landing, California, who collaborated with Sumitomo
in part of the research.
Rusting of ballast tanks as a result of exposure to
seawater is a big problem for the shipping industry. Painting
is the only way to prevent corrosion, but this is expensive
and time consuming. During the approximately 25-year life
of a shipping vessel, painting and maintaining the ballast
tanks generally costs more than U.S. $10 million.
Low oxygen levels in the ballast water reduce rusting
and corrosion by 90 percent.
Tamburri said that deoxygenation would save a ship owner
an average of $70,000 a year, theoretically, at least,
extending the life of the vessel. He estimates the system
would cost about $9 million over the life of the ship.
Although it's too early to determine whether using nitrogen
to clear oxygen from the water will have any adverse environmental
effects, the researchers say major negative effects are
unlikely. Nitrogen makes up 78 percent of the atmosphere
and deoxygenated water poses no threat.
The results of the research are published in the January
issue of the journal Biological Conservation.
To test the effects of low oxygen levels on organisms
in ballast water, Tamburri and co-author Kerstin Wasson
simulated the conditions in ballast tanks. They investigated
the effects of deoxygenation on the larvae of three diverse
and devastating invasive species: the Australian reef-building
tube worm (Ficopomatus enigmaticus), the European
green shore crab (Carcinus maenas), and the zebra
mussel (Dreissena polymorpha).
After two days of exposure to low oxygen levels in the
water, 79 percent of the tubeworms, 82 percent of the
zebra mussels, and 97 percent of the green shore crabs
"It's not perfect," Tamburri said of the approach. "It
doesn't kill everything. But until international law mandates
that ballast water contain no living organisms, why not
require this technology that saves industry money and
is also good for the environment."