In "The Open Boat," what does the shark symbolize?

You are only allowed to ask one question so I have had to
edit down your question. Please do not ask multiple questions in
future.

You might want to think how the presence of the
shark ties in with a wider theme in this excellent short story, which is the age-old
conflict between man and nature. Crane seems to emphasise the incredibly precarious
situation that the men are in by showing how helpless they are in the face of the might
of nature. In the context of the times, mankind had experienced the Industrial
Revolution and the age of Reason, where more and more about science was being
discovered. However, in spite of all the power that mankind had discovered, the men in
the "open boat" are still shown to be incredibly powerless in the face of
nature.

One way that this is manifested is by the presence
of the shark. Note how it is described:

readability="12">

But the thing did not then leave the vicinity of
the boat. Ahead or astern, on one side or the other, at intervals long or short, fled
the long sparkling streak, and there was to be heard the whirroo of
the dark fin. The speed and power of the thing was greatly to be admired. It cut the
water like a gigantic and keen
projectile.

Note how the
narrator focuses on the beauty and strength of the shark. It is shown to be elegant,
graceful and all-powerful in its environment, like a "gigantic and keen projectile." The
men are forced to realise that this is yet another example of how puny they truly are in
the face of nature, where at any moment, a wave or a shark could be the end of
them.