I think your theme is so cute, and the message behind it is really powerful. I really like how you included the summary of findings at the end to remind people of the situation hermit crabs are facing. I also like your environment setup which allows the player to walk from the beach into the water. It makes the whole experience very real and immersive.
One little advise about the audio, I think you can probably make the ambient sound louder. When I start the game, I had to maximize my volume to barely hear the ambient sound, then when I collected the first shell, the sound effect is too loud that it scared the shit out of me hahahaha so I think you can probably balance that a little bit. Now I think the ambient sound just goes from very quiet to completely gone towards the end. Other than that, love your game!