Every year we get news of toxic algal blooms killing fish or making water unsafe to bathe in or drink from, but why do algae produce these toxic blooms? The easy answer is that they kill off predators, so the algae survive. Effectively, the toxin is there as a defence against predation. The problem with this theory is that micro-algae have to divert a lot of energy to produce toxins, so in most scenarios the toxic algae would be out-competed by species that did not go to the trouble!

Recently scientists have uncovered a more aggressive reason for toxin expression by algae, and one that gets round this problem. In the new theory the toxin is actually expressed against other algae in the water. Once killed, these dead phytoplankton leak nutrients back into the water that can be used to help fuel a toxic bloom.

From Science Daily Headlines