Route 128 is another short route, acting as nothing other than a path to your destination. Speaking of which, the next major area is under the waves here - the Seafloor Cavern.
Items
Heart Scale - On the smallest norhern Island, near the Cool Trainer. (Hidden)
Heart Scale - On the west side of the ring-shaped island in the route's center. (Hidden)
Heart Scale - On the south side of the southwestern-most island. (Hidden)
Protein - On the rock in the small Dive spot, at the center of the ring-shaped island. (Hidden; Requires Dive)
Pearl - On the rock in the eastermost Dive spot. (Hidden; Requires Dive)