Which of the following is not a way humans have directly impacted coral reefs?
a. overfishing
b. tourism
c. algae farming
d. agriculture

The correct answer is - c. algae farming.

The algae farming has not been one of the factors that has contributed to the destruction of the coral reefs. The algae farming has either been taking place inland at special facilities where there are special pools for them, or in a strictly regulated conditions in the sea, near the shores.

The corral reefs have been heavily affected by the overfishing because the food chain has been disrupted, by the tourism and the pollution and unawareness of the tourists that come with it, the agriculture with the heavy usage of pesticides, herbicides, fungicides, that get into the water and end up in the sea, as well as the global warming which is changing the temperature of the water.