Algal blooms can be harmful without being
toxic. Some of these non-toxic HABs can kill fish and other
marine organisms by creating unhealthy ecological conditions.
For example, during "Brown Tides," grazers that normally
eat certain species of phytoplankton stop doing so and
starve to death. This results in less food being available for
those organisms higher up the food web.
Another example of a non-toxic HAB is the Chaetoceros-related
bloom which mechanically injures or kills fish. The exact
causes of other non-toxic HABs -- such as Heterosigma-related
and Pfiesteria-related "Fish Kills" -- are still