Definitely an interesting interpretation of the theme. It fits for sure and it's got an interesting game loop which was quite fun to try and get a high score with. I will say as though there does seem to be some risk vs reward with how the plankton spawns. Though there's not much strategy that at least from what I can tell, could be employed, since you're not above to really get a broad picture.
You're generally reacting quite quickly to sharks, unless you move them off screen quite fast. Which did happen to me a bit so that was nice. Though it seems like the plankton spawns relative to you.
Which means that if you have the sharks off screen you're likely missing out on plankton. I could be wrong on that it just seemed as though when I strayed near one place the plankton popped up in the same spawns a decent amount of of times. I also assume it could be used to avoid using a finite map, by making sure all the spawns are near you and so the map can sort of "move with you".
Overall though, an interesting high score based game, that has a bit of strategy to, though I didn't really use the split up the school mechanic that much. It did seem to have some potential.