Energy is the currency of the cell, just like money is the currency of our society. Please compare the process of energy transfer in photosynthesis & cellular respiration with the process of money transfer through our banking system.

Gases enter the atmosphere and trap the sun's heat warning the earth.

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.