Why are invasive species dangerous to the environment?
a they pollute the environment.
b they are voracious predators.
c they threaten biodiversity.
d they are nonrenewable.

Invasive species are dangerous to the environment because they threaten biodiversity. The correct option among all the options that are given in the question is the third option or option "C". These invasive species kill the native plants or animals and this makes a huge difference to the biodiversity of a place. 

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.