If the concern is that the water will lift the dock sections off the structural framing, then you can solve that by installing hurricane straps, linking each component to the next.
Any lumberyard will have them in stock. Long straps wrapped around the poles to the beams and then "hurricane clips" from the beams to each deck joist.
The hurricane clips you would need would be the H2.5AZ's or the H1's:
http://www.strongtie.com/products/connectors/H.asp
The strap for the pole to beam connections: could be as simple as a metal band wrapped around and attached at each end to the cross beams or a cable system. Just don't use eyelets that you would buy at the hardware store, they are not rated and will likely fail if tested by uplift (not likely given the pictures.
For the posts, I would not bed them in the lake bottom for reasons of ice damage and water saturation fatigue in the posts. If you are looking for a simple system that will add a structural element to them (for boat tie off) then I would suggest using these:
http://www.strongtie.com/products/connectors/dptz.asp Bolt the plates to your joists and use structural screws (GRK Screws)to anchor into the post. The beauty of this system is that you will have the ability to remove the posts without having to remove the carraige bolts (requires getting into the water). Use two connectors per post. You can paint these connectors black and it will add a nice clean and finished look to the install.
All hanger nails need to be rated Can't Sag Nails i.e. Joist hanger nails. Leave the common 8D's in the box for this project.
Also add your post padding to ensure that nothing is able to scratch up the boat.