Algae bloom: a rapid increase in the numbers of algae, caused by ideal conditions for reproduction and growth. The problems caused by the boom depend on the species but can include poisoning other species through toxins released by the algae, or upsetting feeding patters of algae eaters. When the algae die, the related decomposition by bacteria uses up oxygen in the water creating anoxic zones, killing other species.  Respiration of the algae at night can create the anoxic zones even before they die.