Hypoxia and Medicine

Help with Biology Question?

How did the Gulf of Mexico's dead zone form? A. All the fish and invertebrate species migrated elsewhere. B. An oil spill killed all the species there. C. Fertilizer runoff from farming caused populations of algae to grow exponentially. D. Hurricanes destroyed the coastline.

Public Comments

1. I don't know anything about this event, but I would assume that the answer would be B or C. I lean more toward B, because oil spills mess up diatoms, which are the primary producers in a marine ecosystem. Lose them and you lose the fish. A wouldn't make too much sense (the migration would have to have a cause) and D wouldn't matter, since we're talking about a marine ecosystem. Therefore, the best answer appears to be an oil spill, or letter B. Hope that helps answer your question! EDIT: So much for that brilliant looking response... I just researched dead zones and the cause apparently appears to be fertilizer runoff in most cases- I would therefore guess that C is the answer.
2. The answer is C. Fertilizer is full as phosphates as well as fecal matter, so the same problem can develop when raw sewage is pumped into an area. Algae begin to grow exponentially removing oxygen from the water. Once this occurs then organisms in the area no longer have enough oxygen to survive so they must be able to move or die. This has occurred in waterways within the US as well.
3. You just have to consider all the options logically: A. Why the hell would they migrate elsewhere? That's just stupid... B. The thing about oil spills is that they are temporary. And ecosystems recover from temporary things. The species will return. C. Fertilizer runoff sounds like more of a long-term effect, making it near-impossible for recovery. And if the algae have grown so much, then that means that the populational composition has completely change, so it may no longer be possible for the species to return, even if the farmers stopped. D. A temporary effect. There is always recovery. In fact, they can even promite diversity (but cutting back on the dominant species). So, if you think through the options, you can normally narrow it down to about two options. And if you can't narrow it down further then at least you are closer to getting it right ^_^