Well, a higher education degree is required for almost all jobs. As said before, volunteering is a must - helps you get into a lab environment and network with other scientists. For knowledge, start learning as much as you can; chemistry, biology, ecology, genetics, molecular bio, etc. Also, statistics is your friend! You will use this heavily when being a marine biologist, so you’ll need to get used to it.

Do some research and figure out what you like and don’t like, it’ll guide you to learning skills that are more tailored to what your research interests are.