In Marine Science it's hard to avoid interdisciplinary crossovers. Choose your subject well - this is most of the battle. Discuss your subject with the faculty. Get their ideas and reactions. Ask them for references or slides.
People are often satisfied to recognize their own suggestions in a student's presentation.
If you are on top of your material, you can be more confident and more relaxed. If you prepare a lot, it can look like you did it all off the top of your head. There is a limit. Don't be so laid back that you send your audience into transcendental meditation. There's no substitute for good scholarship.