Algae play a vital role in the marine ecosystem. They provide food for all sorts of species, but in rare instances, they can also do harm. Harmful algal blooms occur when colonies of certain types of algae grow out of control and produce toxins that enter the food chain through fish and shellfish. Eventually, the toxins can kill larger marine animals like sea lions, manatees, turtles, and dolphins. It also makes shellfish unsafe for human consumption.