Half the year, I lived in Michigan and the other half I worked in Florida. Do I need to file in either state if my income is under $8,000 for that specific state?

Florida does not have state income tax.
If your are considered resident of Michigan, then you will report your worldwide income on Michigan tax retrun. Read state web site for residency requirements and filing requirements.

If you are present in a state, then any income earned during this period, must be reported to the state.

To your resident state, you must report your worldwide income for the year. Read: Your U.S. Tax Return: Working or Living in Two or More states (http://taxipay.blogspot.com/2008/06/working-in-two-or-more-states.html)