Stephen Crane's wrote from a Naturalistic perspective. What this means is that he upheld specific characteristics and beliefs regarding how life was portrayed in his texts.
Essentially, the Naturalist believed that life needed to be portrayed as it really was. Therefore, the setting and characters were realistic, the action was believable, and nature was powerful. The narrator of the Naturalistic text was an observer, meaning they only described what they "saw" and did not interfere with the action of the story.
That said, the symbols found in Crane's short story "The Open Boat" are very important when examining it through a Naturalistic lens.
The wave, sea and shark all represent nature in the text. The boat, on the other hand, represents mankind (given mankind created the boat). This sets the conflict in motion. The men are stranded in the boat, or dingy as the text calls it, upon the sea surrounded by waves and sea life. Given that this is a Naturalistic text, nature is far more powerful and takes front stage to the men and their boat.
The imbalance seen, with the small nature of the men and the vastness and grandness of nature, illuminates the power of nature from the very beginning. For the Naturalist, nature's power always won out over man.