When I started university, marine biology and fisheries where for me the logical options, and while I did Biology in High School, it was not too deep.
I remember vividly how biochemistry and cytology at Uni just blew my mind, and I could see how the challenges of complexity and incredible pathways that already exist at molecular level would extrapolate and amplify... so managing populations and ecosystems is from that angle a mammoth task.
Here is to biochemistry and cytology!