For thousands of years, people have lived on coasts. making a living by shipping goods or by fishing. Today, fisheries in the Gulf of Mexico provide jobs for thousands of people and food for millions more. Although humans and other organisms depend on the ocean, human activities can harm marine ecosystems. Scientists have been tracking dead zones in the ocean for several decades. Dead zones are large bodies of water that are unsuitable for living organisms. They hypothesize that these zones are a result of human activities on land.
A large zone in the Gulf of Mexico forms every year when runoff from spring and summer rain in the Midwest drains into the Mississippi River. The runoff contains nitrogen and phosphorus from fertilizer, animal waste, and sewage from farms and cities. This nutrient-rich water flows into the gulf. Algae feed on excess nutrients and multiply rapidly, creating an algal bloom.
