(quickly)
a mystery organism consists of one cell. it could be a protist or a prokaryote. what single fact about the mystery cell would allow you to determine which type of organism it is? explain your answer.

Whether or not the cell has a nucleus. A protist is a Eukaryotic cell, so it has a nucleus, a prokaryotic cell does not have a nucleus.

Of the cold they can survive in the cold

Although i don't know what is the simulated system, starfish are predators that eat mostly  microalgae,  snails, sponges, bivalves, mussels and other small marine animals. removing starfish from any system would definitely increase this animals that they prey.