Great work here, and absolutely fantastic for your first game jam! I love the art to this.
It took me a couple of deaths to figure out and start putting together some strategies. And I definitely found myself hoping for a upgrade that would let me swim after missing the raft a few times :D.
Also I think a warning for when the core is being attacked would be very handy too.
Nice work with this once again. I think it would be a great one to expand on post jam.