Hi Mikefluff,
You will find some fantastic sea food in Cala Dor but not necessarily restaurants that are wholly seafood. The best restaurants for sea food are the Mallorquian restaurants, which also serve excellent meat dishes and paellas.
In town itself, Can Trompe has some excellent sea food dishes, such as Dorada Mallorquina, which is Dorada or Gilthead, on a bed of Tumbet, baked in the oven. Tumbet is a Mallorquian dish almost like Rattatouie. This is a dish that you will find on many Mallorquian restaruants in the area, with Dorada or other fish. Another speciality is Piementos Rellenos - which is peppers stuffed with seafood - quite delicious. Can Trompe also serves fish in a Salt Crust - the fish is steamed in a salt crust and then broken open and served at your table. The fish is deliciously tender and moist. Again, this dish will be served in all of the restaruants I recommend. The Seafood Paella at Can Trompe is, in my opinion, the best I have had in the area.
In the town of Cala Dor, Restaruant Vicente, which is near the Sa Marina hotel also serves excellent seafood.
On the Marina, I would recommend Botovara, which is on the Cala Egos side of the marina.
There are 2 new restaurants on the marina - one called Las Gambas on that Cala Egos side of the marina, and one called Gados, both of which have lovely menus and I have heard good reports about them but not tried them yet.
I would also highly recommed Maritimo in Porto Petro - Porto Petro is a lovely fishing port about 2 miles from Cala Dor.
Hope this helps.

Vicentes is one of the oldest and most popular retaurants in Cala Dor -- well used by locals who know the good places -- http://www.restaurantvicente.com