DNA isn't really a species-specific thing. There's no way you could tell that a sequence of DNA from a starfish was actually from a starfish without comparing it to the DNA of other starfishes.
And extra DNA doesn't cause mutation. Mutagens, radiation and miscopying cause mutations. Additional DNA is usually far more beneficial than harmful, because it can provide extra resistance to pathogens, as #44406327 said.
Also, jeez, you sound like a conspiracy theorist.