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:
“Virtues are not emotions. Emotions are movements of appetite, virtues dispositions of appetite towards movement. Moreover emotions can be good or bad, reasonable or unreasonable; whereas virtues dispose us only to good. Emotions arise in the appetite and are brought into conformity with reason; virtues are effects of reason achieving themselves in reasonable movements of the appetites. Balanced emotions are virtue’s effect, not its substance.”
—Thomas Aquinas (c. 1225–1274)
“If I had any doubts at all about the justice of my dislike for Shakespeare, that doubt vanished completely. What a crude, immoral, vulgar, and senseless work Hamlet is. The whole thing is based on pagan vengeance; the only aim is to gather together as many effects as possible; there is no rhyme or reason about it.”
—Leo Tolstoy (1828–1910)
“The machines that are first invented to perform any particular movement are always the most complex, and succeeding artists generally discover that, with fewer wheels, with fewer principles of motion, than had originally been employed, the same effects may be more easily produced. The first systems, in the same manner, are always the most complex.”
—Adam Smith (1723–1790)