Global shipping industry: Transporting microscopic invaders

Invasive marine species find a free ride across oceans in a ship's ballast tank, but these stowaways can cause serious problems when they propagate in their new home.

Credit: John Parker

Every year, 110,000 commercial ships arrive to U.S. ports. Along with shipments of cars and computers come some less desirable voyagers: invasive species. They live in the ships’ ballast tanks, which are filled with water to weigh the vessel down when there’s no cargo.

Whitman Miller is a research scientist at the Smithsonian Environmental Research Center’s Marine Invasions Lab, and director of the National Ballast Information Clearinghouse, which collects and analyzes ballast water treatment information from commercial ships. He says that more than 500 species have invaded U.S. waters, and the rate is increasing.

So what’s being done to deal with these stowaways? I spoke to Miller recently about how much damage can be caused by microscopic organisms and what the shipping industry and Coast Guard are doing to tackle them.

When you talk about invasive species being carried in the ballast, we’re not talking about fish, right? More like algae and microbes?

Yes, for the most part, small organisms and organisms in the larval stage. Once in a while if a ship is really not well maintained, the screening they use to keep fish out doesn’t work. We’ve sampled tanks where we’ve found fish 18 to 24 inches long. That’s the extreme.

So how much damage can these tiny organisms really cause?

Plenty. The best known example is that of the zebra mussel [being inadvertently introduced to] the Great Lakes, which came in with ballast water in the ‘80s and caused a lot of economic damage. One day people went to turn the water on in Michigan, and it didn’t come out because the pipes were clogged with zebra mussels. They are filter feeders, so they are filtering out many of the natural things, like the phytoplankton, which can have cascading effects on the ecosystem.

Credit: Smithsonian Environmental Research Center

Maybe this is a silly question, but how do you know the invasive critters arrived in ballast water?

Nobody knows for sure because nobody saw the larvae get off the ship.

But the probability is very high. Even as far back as the ‘30s there was talk about zebra mussels invading the Great Lakes through ballast, but it was never a problem until the 80s. The other possibility is hull fouling [where organisms attach themselves to the hull of a ship], but the likelihood is quite low, because they don’t do well in high salinity water, and they’d have to transit the Atlantic. The short answer is that almost never do you know the vector for sure, but it’s a matter of probability.

Why is this becoming a problem now?

Before the 1880s all ships were wooden hulled vessels so they didn’t have ballast water. They used bricks or gravel—called dry ballast. Shipping was very different. They might spend 30 to 60 days at a port, whereas today a ship that spends more than 24 hours in port is losing money. In the 1880s shipping technology produced the first steel hulled vessels.

The other thing that happened is that someone had the bright idea that instead of using rocks and bricks as ballast, why don’t we just take on water? It’s a brilliant engineering idea, but then you transport these wholesale communities.

Ships arriving from overseas are now required by law to do a ballast water exchange, where they exchange their coastal water for seawater in the middle of the ocean. Why is this effective?

The purpose is to set up a habitat mismatch. The potential for [coastal organisms] surviving in the open ocean is going to be low, and the same is true if you introduce pelagic organisms in the coastal waters. We know ballast exchange removes 95 to 99 percent of organisms, but if you started out with a really huge number, 1 percent could still be a large number of organisms.

Is it perfect? No, but we think it’s the best stop gap. It’s better than doing nothing.

How expensive is the ballast water exchange for shipping companies?

If you have a large ship with multiple ballast tanks, they have tanks on the side—port and starboard—and on the bottom. They can’t just exchange it all at once. You have to do a little here and there. It’s a choreographed procedure and it can take up to 48 hours to exchange all the water. The good news is that they can do it along the way, so it doesn't add an expense from slowing their forward progress. It does add probably a minor expense to running the ballast pumps.

How much ballast water and organisms are we talking about that are released in U.S. ports?

It’s a bit mind boggling because of the scale. Likely there are thousands and thousands of individual species moving around in ballast tanks.

  • Every year, 110,000 commercial ships arrive to U.S. ports.
  • Of those, 50 percent are overseas arrivals and 50 percent are coastwise arrivals (i.e. Boston to New York).
  • Overseas arrivals release about 50 million metric tons of ballast waters per year into U.S. waters that is sourced in waters that are well outside U.S. ecosystems and have the potential to bring non-natives into the U.S.

So how are these ships checked to make sure they are releasing salt water and not coastal water?

Yeah, that’s the issue. The Coast Guard is in charge. In some cases they take a sample of ballast water and check it for salinity. If a ship came from Rotterdam to the U.S., and they checked the water and found it was 37 parts per thousand (which is about that of seawater), that would [be consistent with] it being seawater. If it was 18 parts per thousand, there’s no way that could be seawater. But the salinity is not perfect. If you take water out of Los Angeles Harbor, it’s very close to seawater, so it’s hard to tell.

Are there any new technologies that would make it easier?

The Coast Guard is looking at handheld instruments that can take real time samples [of the chemical fingerprint of the water] so they know within three minutes. Right now they have a handheld, but it just tests the salinity, which isn’t always accurate. I’m encouraged by the technology that’s becoming available.

Will the ballast water regulations affect the way ships are built in the future?

In the fall of 2009 the Coast Guard released a proposed regulation of a discharge standard such that ships will only be allowed to release so many organisms. So you come up with a better treatment system. Ballast water exchange is one step in that direction. At this point I think everyone is moving toward onboard treatment systems: You take on ballast water, and if that water’s been treated in the ballast tank such that you’ve killed the organism before you dump the water back out, that ship can operate anywhere in the world without fear of introducing species.

With these discharge standards, engineering companies can invest money to develop onboard systems, so now we should see some progress.

Whitman Miller image: John Parker

Ship image: Smithsonian Environmental Research Center

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