As to what effect it will have even if we still have one third of the tidal movements.....
it will have a great impact on the small plankton that supports just about all ocean life. Thousands of shellfish species around the world rely on ocean currents created by tidal movements to bring up/in the food they filter from the oceans. Hundreds of birds species rely on the shellfish and worms exposed on tidal flats. Many sea creatures (fish and mammal) live mainly on crustaceans that get their food from the tidal effects, so yes, the change will be great as it changes a large food chain.
Luckily, as dundurn pointed out, evolution will be able to cope with the gradual chance.