As you head north, swing through Ruskin (north of Bradenton) and check out EG Simmons Co. Park. Sites have channels to Tampa Bay, quiet "old" FL park. Last year $18 for sr. cit.
Then travel up the road to Apollo Beach and check out the manatee viewing & interpretive center at the power plant / big smoke stacks. Saw on news tonight they counted 300 manatees there today! They float around in the warm water coming out of plant when it is cold snap like this.