the open boat

I would say so. Romanticism includes the relationship man's relationship with nature, which is also called naturalism. The four men are always struggling against something; waves, sharks, their muscles, their psyche, their acceptance of a nature they don’t control. Check out this link:

http://www.theblackandblue.com/2008/04/09/on-american-naturalism-and-stephen-cranes-the-open-boat/