I am a geographer, and "environmental science" is really just part of the traditional umbrella of geography that's been rebranded. Geography gives a good broad base for going on to specialise in any environmental topic.
If you're dead set on marine conservation already, do have a look for more specific BSc courses. Plenty of universities offer BSc Marine Biology that might be more appropriate if you want to specialise early on. I will say though that because you have a few years to work with in going through undergrad, it still might be worthwhile going for something a little broader to begin with and honing later. I started uni strongly leaning to physical geography, then took lots of modules leaning toward human/social geography, and ended up working in fields on both sides of the socalled human/physical divide. Even if you don't drastically change your direction, it can be nice to have a well-rounded grasp of a subject like geography as a base.