Question

In coastal marine environments, high concentrations of nutrients from terrestrial runoff often lead to algal blooms. When the nutrients are depleted, the algae die and sink and are degraded by other microorganisms. The algal die-off may be followed by a sharp drop in oxygen in the depths, which can kill fish and bottom-dwelling invertebrates. How do these "dead zones" form?

Short answer

The aerobic organisms present in the depth of the ocean feed on dead algae. The gradual growth of these organisms reduces the level of oxygen in the water due to their metabolic activities. As the oxygen level begins to diminish, it poses a severe threat to the existence of other aerobic creatures. This eventually results in the so-called "dead ocean zone."

Step-by-step solution

Algal blooms

Algal blooms are frequently caused by high concentrations of nutrients from terrestrial runoff in coastal marine environments.When nutrients are depleted after planktons or algae consume them, they die and sink, where other microorganisms degrade them.

Formation of “dead zones”

When algae die, they provide food for other smaller organisms in the ocean.As the number of these aquatic organisms grows, so does their need for oxygen to carry out their metabolic activities. The ocean gradually degrades into anoxia. Eutrophication, which happens when a body of water absorbs an excessive amount of nutrients like phosphate and nitrogen, results in the formation of dead zones.

The algae will perish if the nutrients are low. If the algae die, the oxygen content drops dramatically. These effects kill fish and bottom-dwellers. The dead algae are a source of food for aerobic organisms. If the number of these algae grows, so do the people who consume them. These consumers are top and medium-feeders, so they'll take in more oxygen. This has an impact on bottom-feeders. As a result, the dead organisms form the dead zones.