What are 4 ways bacteria and viruses can be transmitted?

Bacteria can be transmitted by contact, ingestion, breathing in, and can also get inside open cuts in the skin. viruses ingested, air born which means you can breathe it in, you coming in contact with someone or something infected by the virus. you can also contract it from your environment in some cases. 

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.