What characterizes areas defined as hypoxic zones?

Hypoxic zones are characterized by low levels of oxygen in the water, which can create significant stress for marine life. When oxygen levels drop, aquatic organisms, particularly those that are sensitive to oxygen fluctuations, struggle to survive. This condition can lead to fish kills and a decline in biodiversity as many species cannot thrive in these low-oxygen environments. The primary cause of hypoxia often links back to nutrient pollution, which can stimulate excessive algal blooms; when these blooms die off and decompose, oxygen is consumed in the process, further depleting the oxygen available to marine life. Thus, option B accurately reflects the defining characteristic of hypoxic zones.