There are 3 types of concrete placement in relationship to salt water: 1) submerged, 2) splash, and 3) atmospheric.
As you can imagine, the severity of design against the salt environment is critical for each situation. I believe you fall in category 2) splash, because you indicated your foundation will be on “exposed bedrock”.
There are many considerations for such an installation, like concrete design, additives, cover from face of rebar to edge of footing (top, sides and bottom), control joints, tie into existing foundation, etc.
Here is a great article to help you:
Remember, concrete is porous. “Cover” will be one of the most important decisions you’ll make. The article recommends a 2” cover. I live in a very corrosive atmosphere and we do not go below 3”..I highly recommend 3” minimum.
BTW, I would not “tie” your new foundation to the bedrock, unless you’re positive the existing foundation is. I’d just rest it on bedrock, because in case of ANY seismic activity, the rock will go one way and your house will go another (due to weight, depth, etc.).