The nobles are on the Shabondy Archipelago (the islands they're at now) and not Merman Island...and wow, they're a lot nastier than I would have thought
(from ArlongPark)
Luffy walks with Hacchan.
Hachi: The World Nobles are also called the Tenryuubito (Translates to Heavenly Dragon People). They are arrogant, and wear masks so they won't have to breath the same air as rest of the people. One thing to keep in mind is to not stand up against them. This island is where people going to the New World gather. Naturally, the Marines and the Bounty Hunters here are all fierce and capable ones fitting the level of this place!
Luffy and Hachi play at the bubble store. They race each other on a bubble bicycle. A pirate spots them from far away, and comes running towards them asking for help. He has a collar on his neck.
Akumate: Please! Please, I'm asking you please! Anyone, give me an axe or a saw!! I won't hurt anyone, I just want to break off this collar!! I gave up on the New World!! I have a wife and a son back in my homeland!!! My son's still a baby... The brat doesn't even know my face, dammit!!
It [the collar] explodes.
Captain Akumate, a 60,000,000 berry bounty pirate, dies from the explosion.
The Heavenly Dragon People treats his corpse like a worthless bug.
Luffy: Whoa!?
Hachi: The slaves always have the collar around their neck.. if you break the chains and run off, the collar will explode...
The noble lets their dog pee on the body, and he himself shoots the body, saying how disgusting it is.
In the last page, Luffy snaps seeing how they treat the dead pirate, and tries to attack them, but Hachi holds him back begging him to restrain.