From the diving bell head south to a Treasure while avoiding an eel and then return to the bell. Look to the northwest to spot a temple ruins with some seaweed on the ocean floor and swim down to the patch. From here, head around the front of the ruins and enter the doorway and carefully make your way to the Treasure with the Elite Round Shot Design Plans. Exit the way you came in and swim up to the top of the temple for an Animus Fragment before returning to the bell for some air.
Head back down to the seaweed and then swim town the front of the temple toward the air barrel and swim up and over the nearby eel to reach the next Treasure. Continue into the tunnel and stop at the air pocket and then take a right down a long corridor. The current here will push you back at regular intervals and is proceeded by an "earthquake". In order to reach the end of the tunnel you will need to swim into an opening on the right side of the tunnel to avoid the current and reach the end, getting a Treasure in the first gap and reach an Animus Fragment and air pocket on the second. Return to the tunnel entrance and leave.
As you leave the tunnel, avoiding the eel again, head right to a patch of seaweed and when the sharks turn away follow the ditch down to another Treasure and then get some air at the nearby barrel. Turn around and hug the wall on your left to swim to some burst beams and propel yourself forward and into the seaweed at the bottom of the area.
Get some air if you need it and then swim inside the nearby wreck, avoiding the sea urchin and eel, and grab the Treasure. Return to the seaweed and then head up and over the bow of the shipwreck nearby to reach the Animus Fragment on the other side and get some air from the barrel. Keep swimming along the sea floor to the seventh Treasure and then wait for the shark to pass before making a break to the air barrel on the left. From the barrel, use the burst beam to reach the next temple entrance and exit the other side to get the final Treasure on the sea floor. You can now return to the diving bell and return to the surface.
