In 2011 and 2012, scientists working on the Banana River in Florida recorded a dramatic increase in the number of manatee deaths. Over the past 50 years, this area has also seen the human population increase by more than 500,000 people. It is believed that pollution from numerous sewage tanks leaked into the water, eliminating the manatees' food source, replacing it with an alga that is toxic to the manatee. This is an example of A) a natural cycle in an ecosystem B) the effect of increased biodiversity on an ecosystem C) human actions altering ecosystems with serious consequences D) direct harvesting in an ecosystem

The increase in the number of people during the last 50 years to more than 500,000 individuals, and probably the lack of policies and regulation, lead to an enhance in water pollution by sewage tank leaks.

Pollution probably caused a gradual decrease in the manatee´s principal source of food, which also caused an increase in the toxic algae population.

Algae caused the death of manatees as a consequence of human action that altered the natural ecosystem by polluting water.