What is the main source of energy for most processes at earths surface

Carbohydrates.
Carbohydrates actually get stored in the form of long polymers of glucose molecules or as glycogen starch. They provide energy to the animals for performing their daily duties. Carbohydrates are generally considered the fuel for all organisms, and without this most animals would become sloth and would be unable to perform the regular jobs. Carbohydrates are actually very easy to metabolise and hence generate quick energy.

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.