Masters in Marine Biology with unrelated course.

Hi everyone! I’m looking for some advice. I’m debating whether to pursue my dream of studying Marine Biology, even though my undergraduate degree is in Criminology. The two fields aren't directly aligned. I graduated with my Criminology degree three months ago, but it wasn't my dream program; I only chose it because I felt overwhelmed at the time and didn't feel like I had any other options.

1. What subjects will I need to take?

2. Is it difficult and how long will it take?

3. What careers will I pursue?

   All your advice are much appreciated.