The brown tide algae Aureococcus and Aureoumbra can stop other types of algae from growing. They release chemicals that reduce the number of competing algae by up to 96%. The more brown tide algae there are, the stronger the effect. Newer strains of Aureoumbra are even better at this than older ones. These chemicals can last for a while and are different for each type of brown tide algae. The chemicals can also affect natural groups of algae in the water. This shows that the brown tide algae use allelopathy to make harmful algal blooms worse.