Fertilizer runoff from the Mississippi River and in the Florida Everglades causes large plumes of red algae to flourish. The overgrowth of these plants reduce the amount of sun to other plants which then die and decompose. The decomposition of these plants creates a greater demand for oxygen, thus depleting the area and creating dead zones. Harmful algal blooms also produce toxins that are dangerous to marine life and humans. Animals such as bivalves can accumulate these toxins and if eaten can cause serious health problems for the consumer. Wildlife cannot flourish here because the oxygen levels are too low to support them.

Red Tide

Red Tide

Dead zones are often caused by red tides. Dr. José Leal, Director of The Bailey-Matthews Shell Museum, described red tide as follows: “Red tides are caused by large blooms of a marine microorganism called Karenia brevis. Those single-celled organisms release a toxic gas that causes the death of marine invertebrates and vertebrates such as fish and dolphins. Sometimes, during prolonged periods of red tide, the levels of oxygen dissolved in seawater severely decrease, as a result of the deaths of millions and millions of animals in the area.” To read the entire interview, click here.

Resources on Dead Zones