In many ways, battling aquatic invaders is more difficult than dealing with their terrestrial counterparts. Mechanical control requires specialized machinery built to perform underwater or to float on the surface, "physical removal" often means employing trained divers, and target-specific chemical controls are nearly impossible due to the reactive and dispersive properties of water.
Now from Biology News Net comes news that scientists have developed a new, more direct way of delivering toxic chemicals to zebra mussels (Dreissena polymorpha). Called BioBullets, the teeny, tiny microcapsules (about 100 micrometers in diameter each) each contain a small dose of potassium chloride, a compound toxic to the bivalves. By encapsulating the toxin in a mixture of vegetable oil and a surfactant, the researchers have found a way to avoid triggering the zebra mussels' typical response to poison, which is to shut down their filtering system, often for weeks at a time. Interested readers will want to check out the full article (.pdf), and this article from Red Orbit about Gill Kill, which sounds like the same product with a different name. And in case you were wondering, oh yes: BioBullets are patented.