Alien Invaders in our Oceans
We have all seen science fiction movies depicting alien invaders from outer space. With few exceptions the aliens mean harm in one way or another. And while the occasional tabloid claims to have interviewed a person who has been abducted by an alien, few of us take the subject of alien invaders seriously. Not so myself. I take alien invaders quite seriously.
Do I really believe in aliens from space? No, not from space, I'm talking about very small invaders of our oceans,lakes and rivers. Some are plants, some are animals and though it isn't personal, they do cause harm. Most are stowaways, sailing from one body of water to another like a sightseeing tourist.
The aliens have been invading for centuries, ever since man took to boats and especially ships. It all seemed so innocent that no one took it all that seriously until a few decades ago.
Ships use water as ballast. It's not high tech, they simply allow a certain amount of water to run into the bottom of the ship. Ships use the water ballast to adjust their position in the water, improve maneuverability and most of all, improve stability. Ships tend to roll a lot less if they are carrying ballast. The damage happens when whatever life forms the ship picked up with its ballast water, are let out when the ship drains it's ballast water. If the animals or plants survived, they are introduced into a who new ecosystem.
Ecosystems are delicate. Every living thing is part of it's local food chain. But when you take that lifeform and put it into a different ecosystem, it can wreck havoc. Often the introduced lifeform will crowd out existing plants and animals. If there is no way to control the plant or animal, it may reproduce so quickly as to cause irreparable damage to the local ecosystem.
There are, of course, more than one way that alien invaders can be introduced. Sometimes, the plant or animal escapes from captivity. Another way is that the plant or animal was intentionally introduced to the new ecosystem before we understood this was a bad idea. But by far, most have been introduced by ship's ballast water.
is from Asia but is now covering reefs in Florida and the NW US. Comb Jelly,
native to the North Atlantic was introduced to the Black Sea from ballast
water. Once there, it competed more successfully for food than the native
fish. It also killed a larvae native and helpful to the Black Sea. Cholera
bacterium came from South American to Alabama by ballast water in 1992.
Since then, it has closed local shellfish beds and actually become a health threat. The Green Crab, native to Asia was brought to San Francisco in ballast water where it has crowded out native crabs.
But by far the worst stowaway in ballast water has been the zebra mussel. This little creature is native to Europe. But it escaped from ballast water to the Great Lakes where it has cost an estimated five billion dollars damage. Zebra mussels more than flourish in the Great Lakes, in fact as many as 700,000 may occupy only one cubic yard.
In 1991, the International
Maritime Organization (a United Nations agency) developed voluntary guidelines
for ballast water. All participating major and medium-sized shipping nations
will take measures to control the spread of alien species. To control spreading
forms of algae, ships are advised to not take on ballast water in heavily
silted areas of algae bloom. Many environmental groups are pushing for
enforceable laws. Only time will tell how much additional damage has been
done from stowaways.
Copyright © 2001 Kathy A. Miles and Charles F. Peters II