Effects of Low Oxygen

A reduction in dissolved oxygen concentration is one of the most important negative effects of nutrient over-enrichment of coastal waters. Low dissolved oxygen (hypoxia) can cause mortality, reduced growth rates, and altered distributions and behaviors of fishes, as well as changes in the relative importance of organisms and pathways of carbon flow within food webs. As a result, hypoxia and anoxia can lead to large reductions in the abundance, diversity and harvest of fishes within affected waters.
      In estuaries, both the degree of oxygen depletion and the effects of low oxygen on living resources tend to be most severe in bottom waters. Nutrient enrichment typically increases prey abundance in more highly oxygenated surface waters and beyond the boundaries of the hypoxic zone. Because of this mosaic of high and low oxygen areas within a system, not only the actual oxygen concentration of bottom waters, but the spatial arrangement, predictability and persistence of highly oxygenated, high productivity habitats, and the ability of fishes to locate and utilize those favorable habitats, will determine the ultimate effect of low oxygen on fish populations.
      Negative effects of hypoxia on fish, habitat and food webs, potentially make both fish populations and entire systems more susceptible to additional anthropogenic and natural stressors.

Low dissolved oxygen reduces the abundance and diversity of fishes in affected areas.