After spermatogenesis, sperm are stored in the

Just after the sperms are formed they are stored in the seminiferous tubules itself so that they get some nourishment. Later on, they are transferred to the epidermis where they are stored till ejaculation. Here, they get matured too.

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.