Effects
Low oxygen levels recorded along the Gulf Coast of North America have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning.
In a study of the Gulf killifish by the Southeastern Louisiana University done in three bays along the Gulf Coast, fish living in bays where the oxygen levels in the water dropped to 1 to 2 parts per million (ppm) for three or more hours per day were found to have smaller reproductive organs. The male gonads were 34% to 50% as large as males of similar size in bays where the oxygen levels were normal (6 to 8 ppm). Females were found to have ovaries that were half as large as those in normal oxygen levels. The number of eggs in females living in hypoxic waters were only one-seventh the number of eggs in fish living in normal oxygen levels. (Landry, et al., 2004)
Fish raised in laboratory-created hypoxic conditions showed extremely low sex hormone concentrations and increased elevation of activity in two genes triggered by the hypoxia-inductile factor (HIF) protein. Under hypoxic conditions, HIF pairs with another protein, ARNT. The two then bind to DNA in cells, activating genes in those cells.
Under normal oxygen conditions, ARNT combines with estrogen to activate genes. Hypoxic cells in vitro did not react to estrogen placed in the tube. HIF appears to render ARNT unavailable to interact with estrogen, providing a mechanism by which hypoxic conditions alter reproduction in fish. (Johanning, et al., 2004)
It might be expected that fish would flee this potential suffocation, but they are often quickly rendered unconscious and doomed. Slow moving bottom-dwelling creatures like clams, lobsters and oysters are unable to escape. All colonial animals are extinguished. The normal re-mineralization and recycling that occurs among benthic life-forms is stifled.
Read more about this topic: Dead Zone (ecology)
Famous quotes containing the word effects:
“If one judges love according to the greatest part of the effects it produces, it would appear to resemble rather hatred than kindness.”
—François, Duc De La Rochefoucauld (1613–1680)
“Trade and commerce, if they were not made of India-rubber, would never manage to bounce over the obstacles which legislators are continually putting in their way; and, if one were to judge these men wholly by the effects of their actions and not partly by their intentions, they would deserve to be classed and punished with those mischievous persons who put obstructions on the railroads.”
—Henry David Thoreau (1817–1862)
“The hippie is the scion of surplus value. The dropout can only claim sanctity in a society which offers something to be dropped out of—career, ambition, conspicuous consumption. The effects of hippie sanctimony can only be felt in the context of others who plunder his lifestyle for what they find good or profitable, a process known as rip-off by the hippie, who will not see how savagely he has pillaged intricate and demanding civilizations for his own parodic lifestyle.”
—Germaine Greer (b. 1939)