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Dead zone (ecology)
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Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 mg of O2/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O2/liter in a body of water, mass mortality occurs. With such a low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated.
Dead zones are often caused by the decay of algae during algal blooms, like this one off the coast of La Jolla, San Diego, California.
Dead zones are often caused by the decay of algae during algal blooms, like this one off the coast of La Jolla, San Diego, California.
Climate has a significant impact on the growth and decline of ecological dead zones. During spring months, as rainfall increases, more nutrient-rich w
Climate has a significant impact on the growth and decline of ecological dead zones. During spring months, as rainfall increases, more nutrient-rich water flows down the mouth of the Mississippi River. At the same time, as sunlight increases during the spring, algal growth in the dead zones increases dramatically. In fall months, tropical storms begin to enter the Gulf of Mexico and break up the dead zones, and the cycle repeats again in the spring.
Underwater video frame of the sea floor in the western Baltic covered with dead or dying crabs, fish and clams killed by oxygen depletion
Underwater video frame of the sea floor in the western Baltic covered with dead or dying crabs, fish and clams killed by oxygen depletion
In many places, coral reefs are experiencing worse hypoxia which can lead to bleaching and mass coral die-offs.
In many places, coral reefs are experiencing worse hypoxia which can lead to bleaching and mass coral die-offs.
Hypoxia (environmental)
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Hypoxia refers to low oxygen conditions. For air-breathing organisms, hypoxia is problematic but for many anaerobic organisms, hypoxia is essential. Hypoxia applies to many situations, but usually refers to the atmosphere and natural waters.
Still frame from an underwater video of the sea floor. The floor is covered with crabs, fish, and clams apparently dead or dying from oxygen depletion
Still frame from an underwater video of the sea floor. The floor is covered with crabs, fish, and clams apparently dead or dying from oxygen depletion.
Jubilee photo from Mobile Bay
Jubilee photo from Mobile Bay