Invading alien species

As international trade increases particularly by sea, we're seeing more stowaways, but not of the human variety.  Scientists are reporting that animals and plants are hitching rides around the world on boats and even on fishing tackle and then setting up home in other countries where, with nothing to eat them, they can become dangerously invasive. 

Invasive species specialist David Aldridge from the University of Cambridge showed Ginny Smith one of the species creating chaos in British waters...

David -   It's just starting to create chaos.  This is something called the quagga mussel.  And it's the species we least wanted to arrive in the UK out of anything.

Ginny -   So, you got a little tube full of them here and they're tiny.  They look a bit like the mussels you might expect with your chips, but they're tiny.  Do they stay that small?

David -   Yeah, don't be fooled by their small size.  They pack quite a punch - these guys.  They are small at the moment because they've just arrived.  They're about a centimetre at the moment here, but they grow to maybe 2 or 3 centimetres.  And the problem really comes from the huge abundance that they can occur at.  They're a real problem because as you say, they're like the marine mussels that we eat.  These are freshwater species, but they have a byssus  thread and they can attach one on top of the other and form very thick crusts, about 15 centimetres.  And that causes a huge environmental problem and also, a huge economic problem.

Ginny -   And what kind of problems are these crusts of mussels causing?

David -   Directly, what they can do is attach to any hard surface and that includes our native freshwater mussels such as in vulnerable species called the depressed river mussel.  It smothers them and kills them.

Ginny -   I can see why it might be depressed.

David -   Yes, they're going to be even more depressed very soon.  Also, a single quagga mussel of about 2 centimetres could filter 2 litres of water a day and they change the nature of the water that they live in so they can push some systems towards a dominance of cyanobacteria - blue-green algae, which is toxic - problems for human drinking, for pets that might go in the water.  But also, in some systems, they can drive the water much clearer.  The light penetrates more deeply and you get more bottom-rooting planting and those plants were often used as weeds which create flood risk, angling problems, navigation problems.

Ginny -   Amazing that something so small can cause so many different issues.  Where are they coming from?

David -   Well, these are really interesting because they're native to eastern Europe from the Ponto-Caspian regions, so the Black Sea, the Caspian Sea.  And the whole of western Europe is being invaded by these species as a result of canal construction which is linked to a lot of the major rivers together.  What we're finding is that as they arrive into the UK that actually, these species are interacting with each other in a positive way.  And so, the arrival of one invader from this region is facilitating, it's making it easier for the other invaders to be a problem.

Ginny -   Why do they cause so much trouble when they're over here and not when they're in their sort of original habitat?

David -   Well, what tends to happen is that they often arrive and they don't have natural predators and enemies and their native range has been lots of co-evolution.  And so, if you like, the system is in a bit of stasis.  Things are settled down.  Often, when they arrive in new areas, they might've escaped from their predators, or their diseases and so, they can proliferate very, very quickly.  And so, these huge abundances drive massive ecological change.

Ginny -   Is this just the case of things coming in or are there any invaders going out from England to other places?

David -   Well obviously, invasive species are not just a special thing to the UK.  It's something which happens around the world.  And we're not just importers of non-native species - we're exporters as well.  A good case is the shore crab which is quite common in British coasts.  It's what children like to go and catch at the harbour sides.  That species has become a real pest in North America.

Ginny -   So, what can we do when we have these species coming in from other places and there are just aren't enough predators to eat them.  Is there anything we can do to prevent them from taking over and damaging native species?

David -   In the UK, we're in a very privilege position in that, we have control over our own waterways.  If you're in mainland Europe then your water can come through 7 different countries.  So, we do have the opportunities to try and control what actually comes into our freshwaters.  And that involves us understanding the vectors and pathways of these pests.  But then it comes down to policy.  On a more practical level, we can manage biosecurity through the transports of freshwater invaders from one river to another.  And that involves engaging with the public to encourage them to check their equipment, their fishing gear, their waders, their boats - clean them down, dry them before they move them from one water body to another.  There are some emerging tools.  We have a product which can kill these quagga mussels called the biobullet which has been successfully used against its slightly less naughty cousin, the zebra mussel in the UK. And the way the biobullet works is that it carries a salt which is toxic to the mussels which is encapsulated in a tasty little particle which is just the right size and shape for the mussels to filter out the water, and they take out this poison pill, and swallow it immediediatly and it kills them. And anything which they haven't eaten degrades to harmless concentrations very quickly. So its a very targeted solution which doesn't impact on humans, doesn't impact on other widlife.