When algae have a huge growth burst or "bloom" they can cause enormous damage to local ecologies. In some cases, such as the infamous red tides involving neurotoxic algae that affect things people eat, the blooms can be deadly. Now Michiel Postema and colleagues at the University of Hull have found a simple way to single out and kill the algae.
Strands of algae keep afloat through the aid of little nitrogen-filled "buoyancy" cells. Postema and colleagues decided to see if ultrasound could rupture the membranes of these cells, causing them to sink and die. Their tests, with the blue-green algae Anabaena sphaerica, showed that the algae sank under the application of ultrasound frequencies normally used in medical diagnostics. One advantage of this process is that standard plant cells, not filled with air, are unaffected.