Alien invasion: Shoot down three Blarg Saucers with visibombs
Buried treasure: Find and destroy all crates in the ocean
You need the Swingshot and the Thrusterpack: from the beginning, follow the path you took when escorting the commercial man, until you get to the first Psytopus. Jump into the water on the right and there should be a place where you can go left under the land. Go under the arc and get out of the water. You will need to make your way through using your weapons, your Swingshot, and your Thrusterpack for a special lock and finally get to the gold bolt at a water cascade.(This is filled with Puffer Fishes and more Psytopuses).