But within the corporate business world, there are also plenty of opportunities for travel: Sales, consulting, management just to name a few. Even a lot of coders I work with travel all around the world to present their projects.
I recently met a chef that is also publishes cook books. He traveled all around the world for his newest book to interview international chefs, and taste new foods.
Essentially, if you'd like to travel, there are sooooo many different paths you can go down! But, in some cases, you may have to advocate on your own behalf to get those travel opportunities once you have the job.
There may be travel opportunities in both of your options, marine biologist and writing. Personally I would think that marine biology might have more travel involved if that's what you want to pursue. In any job I think that this will depend a lot on the company that you're working for and the job description. It's an excellent thing to ask about during future job interviews though. I would definitely recommend bringing it up.
When jobs require travel, it is typical for the company to cover your expenses . But again, this is an excellent question for interviews for positions where travel may be involved.