No!
No, you cannot use Dive in Pokemon Pearl to go underwater.
Use the move dive to go underwater to find shards in the seaweed.
Use Dive.
Since dive is not a HM in firered you will have to trade a Pokemon to a friend that has ruby, sapphire or emerald then using that game use the HM Dive to teach the move Dive to that Pokemon trade it back so firered can have that Pokemon again it will still have Dive however you cannot use it to dive underwater.
When you Surf, you will see dark spots in the sea. You can then use Dive, and go underwater.
underwater just use dive
go to route 127. use dive. it will be there.
You can't "see" them, but they can be found by moving around the seaweed underwater, such as the seaweed around Sootopolis.
You will need the Dive HM which I think you get from Stephen after getting the badge from the Mossdeep gym. Then use Dive out at sea and you can find shards underwater aorund the Mossdeep and Sootopolis areas.
get a hm called dive attach it to a water type pokemon and go on water and use dive.
Use Dive with a Pokemon and Go through the water. You will see a hole. Go inside and Use dive to go to a new place.
In Pokémon Ruby, Sapphire and Emerald, teach a Pokémon the HM move dive and once you're surfing over a dark patch of water, you can use dive to go and stay underwater.