Conducting a census of species using environmental DNA.
A plastic soda bottle might just be trash to you, but to some plants and animals, it's their ticket across the ocean. In this Science Update, you'll hear why that has some scientists worried.
Unwanted passengers on plastic. I'm Bob Hirshon and this is Science Update.
Most people try to ignore the unsightly trash that washes up on beaches. But David Barnes of the British Antarctic Survey studies it. He's spent the past ten years collecting trash that has washed up on remote island shores all over the world.
He examined about 200 items and found a huge variety of organisms hitching rides on the rubbish.
Mollusks, and crustaceans—typically barnacles—and then what we think of as the more weedy species and sort of sea mats. But also occasionally corals.
He says most of the debris he found was plastic, which doesn't break down easily, so it travels far. This means that floating trash could be a significant way for unwanted organisms to travel to distant lands. These invasive species can destroy native plants and animals, and once they get established, they're hard to get rid of.
No marine pest has ever been removed from an environment it has got into. And this plastic and other rubbish that's traveling the globe presents the best opportunity for them to get there. So we must take this problem seriously.
And that means regarding rubbish as not only unsightly, but also as a hazard to the environment. For the American Association for the Advancement of Science, I'm Bob Hirshon.
Making Sense of the Research
This study touches on the growing problem of invasive species. A species is "invasive" if it's introduced accidentally from one environment to another, and starts to thrive there. Invasive species can wreak havoc on an ecosystem by crowding out or preying on native local species. And since invasive species have no natural predators in their new environment, they usually enjoy a competitive advantage over local flora and fauna.
In the summer of 2002, a species of fish called the snakehead, which can actually walk on land, made headlines when it invaded Maryland's waters. Other invasive species, like the zebra mussel, have been a problem in lakes and rivers all over the United States for over a decade.
Zebra mussels are believed to have originally reached U.S. waters from Europe by stowing away in the ballast water of ships. In this report, Barnes discusses another way that invasive species might travel: on garbage. He's not the first to suggest it can happen, but his study helps shed light on the global scale of the problem. Over the past ten years, he's found beach trash infested with stowaway species all around the world.
Barnes' data show that organisms travel best in warmer waters: the closer you get to the equator, the greater the likelihood that a piece of garbage is carrying living organisms. On the other hand, areas further from the tropics, especially in the Southern hemisphere, have less natural debris (like wood and leaves) washing up on their shores. So, relatively speaking, the human garbage actually has a more dramatic impact on the number of invasive species that wind up in these cooler climates.
What's more, Barnes points out that global warming is raising the temperatures of these cooler regions, which means that their last defense—the possibility that invasive species will freeze to death before causing any damage—is being stripped away. He says that humans can help contain the problem by reducing the amount of waste they generate, especially plastic waste, which is not only sturdy but also provides an ideal surface to which stowaway organisms can attach.
Now try and answer these questions:
- What are invasive species? How can they threaten an ecosystem?
- In what parts of the world are the greatest numbers of invasive species coming ashore on marine garbage? In what areas has marine garbage caused the biggest relative increase in invasive species? What accounts for the difference?
- How might global warming worsen the problem described in this study?
- Can you think of other ways that non-native species might be introduced to an ecosystem? How widespread do you think the problem is?
InvasiveSpecies.gov is a site devoted to the U.S. Government's efforts to combat the effects of non-native species.
The University of Wisconsin Sea Grant's Zebra Mussel Watch is a site devoted to the zebra mussel, one of America's most troublesome invasive species.
The United Nations Environment Programme Regional Seas Marine Litter site is a clearinghouse for information about marine trash and its impact on the environment.